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EQUITY METHOD INVESTMENTS (Tables)

12 Months Ended

Dec. 31, 2019

Equity Method Investments And Joint Ventures [Abstract]

A reconciliation of our 38.5% and 40% ownership interest in Ohio Gathering to our investment per Ohio Gathering's books and records follows for the years ending December 31, 2019 and 2018, respectively (in thousands).

	2019		2018
	(In thousands)
Investment in Ohio Gathering, December 31	$	275,000	$	649,250
December cash distributions		2,700		2,736
Impairment loss (1)		232,521		5,652
Loss contingency		—		2,040
Basis difference		—		(116,832	)
Investment in Ohio Gathering, net of basis difference, November 30	$	510,221	$	542,846

(1)

Amount is comprised of (i) a $329.7 million impairment of our equity method investment in Ohio Gathering; (ii) the write-off of our basis difference of ($103.5) million in Ohio Gathering as a result of the impairment in our equity method investment in Ohio Gathering; and (iii) a $6.3 million impairment of long-lived assets in OCC.

Summarized balance sheet information for OGC and OCC follows (amounts represent 100% of investee financial information).

	November 30, 2019				November 30, 2018
	OGC		OCC		OGC		OCC
	(In thousands)
Current assets	$	41,972	$	2,187	$	37,403	$	3,716
Noncurrent assets		1,281,171		28,323		1,262,253		27,203
Total assets	$	1,323,143	$	30,510	$	1,299,656	$	30,919

Current liabilities	$	21,798	$	4,016	$	19,903	$	3,912
Noncurrent liabilities		4,113		6,683		3,688		8,807
Total liabilities	$	25,911	$	10,699	$	23,591	$	12,719

Summarized statements of operations information for OGC and OCC follow (amounts represent 100% of investee financial information).

	Twelve months ended November 30, 2019					Twelve months ended November 30, 2018				Twelve months ended November 30, 2017
	OGC		OCC			OGC		OCC		OGC		OCC
	(In thousands)
Total revenues	$	142,138	$	8,601		$	142,398	$	10,177	$	140,679	$	8,607
Total operating expenses		108,234		38,815			136,722		9,053		111,897		8,298
Net income (loss)		33,897		(30,214	)		5,670		498		28,785		(907	)

CONSOLIDATED BALANCE SHEETS - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 4,948,000	$ 4,345,000
Restricted cash	27,392,000
Accounts receivable	102,118,000	97,936,000
Other current assets	5,018,000	3,971,000
Total current assets	139,476,000	106,252,000
Property, plant and equipment, net	1,882,251,000	1,963,713,000
Intangible assets, net	232,278,000	273,416,000
Goodwill	0	16,211,000
Investment in equity method investees	309,728,000	649,250,000
Other noncurrent assets	9,718,000	11,720,000
Total assets	2,573,451,000	3,020,562,000
Current liabilities:
Trade accounts payable	24,415,000	38,414,000
Accrued expenses	11,482,000	21,963,000
Due to affiliate	311,000	240,000
Deferred revenue	13,493,000	11,467,000
Ad valorem taxes payable	8,477,000	10,550,000
Accrued interest	12,311,000	12,286,000
Accrued environmental remediation	1,725,000	2,487,000
Other current liabilities	11,933,000	12,645,000
Total current liabilities	84,147,000	110,052,000
Long-term debt	1,470,299,000	1,257,731,000
Noncurrent Deferred Purchase Price Obligation	178,453,000	383,934,000
Noncurrent deferred revenue	38,709,000	39,504,000
Noncurrent accrued environmental remediation	2,926,000	3,149,000
Other noncurrent liabilities	7,951,000	4,968,000
Total liabilities	1,782,485,000	1,799,338,000
Commitments and contingencies (Note 16)
Partners' Capital
Series A Preferred Units (300,000 units issued and outstanding at	293,616,000	293,616,000
Common limited partner capital (93,493,473 units issued and outstanding at December 31, 2019 and 73,390,853 units issued and outstanding at December 31, 2018)	469,900,000	902,358,000
General Partner interests (zero units issued and outstanding at December 31, 2019 and 1,490,999 units issued and outstanding at December 31, 2018)		25,250,000
Total partners' capital	763,516,000	1,221,224,000
Total liabilities, mezzanine capital and partners' capital	2,573,451,000	$ 3,020,562,000
Mezzanine Capital
Mezzanine Capital
Subsidiary Series A Preferred Units (30,058 units issued and outstanding at December 31, 2019)	$ 27,450,000

CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Adjustment	At Market Program	Noncontrolling interest	Noncontrolling interest Adjustment	Noncontrolling interest At Market Program	Limited Partner Series A Preferred Units	Limited Partner Series A Preferred Units Adjustment	Limited Partner Series A Preferred Units At Market Program	Common	Common Adjustment	Common At Market Program	General Partner	General Partner Adjustment	General Partner At Market Program
Beginning balance at Dec. 31, 2016	$ 1,169,673			$ 11,247			$ 0			$ 1,129,132			$ 29,294
Net income (loss)	86,050			363			3,563			71,922			10,202
Distributions to unitholders	(181,478)			0			(2,375)			(167,062)			(12,041)
Unit-based compensation	7,878			0			0			7,878			0
Tax withholdings on vested SMLP LTIP awards	(2,236)			0			0			(2,236)			0
Issuance of Series A Preferred Units, net of offering costs	293,238		$ 17,078	0		$ 0	293,238		$ 0	0		$ 17,078	0		$ 0
Contribution from General Partner	465			0			0			0			465
Purchase of noncontrolling interest	(797)			(797)			0			0			0
Other	(202)			0			0			(202)			0
DPPO partial settlement	0
Ending balance at Dec. 31, 2017	1,389,669	$ 1,393,883		10,813	$ 10,813		294,426	$ 294,426		1,056,510	$ 1,060,640		27,920	$ 28,004
January 1, 2018 impact of Topic 606day 1 adoption	4,214			0			0			4,130			84
Net income (loss)	42,351			168			28,500			4,299			9,384
Distributions to unitholders	(209,205)			0			(28,500)			(168,567)			(12,138)
Unit-based compensation	8,088			0			0			8,088			0
Tax withholdings on vested SMLP LTIP awards	(1,974)			0			0			(1,974)			0
Purchase of noncontrolling interest	(10,981)			(10,981)			0			0			0
Other	(938)			0			(810)			(128)			0
DPPO partial settlement	0
Ending balance at Dec. 31, 2018	1,221,224			0			293,616			902,358			25,250
Net income (loss)	(369,891)			0			28,500			(398,403)			12
Conversion of General Partner economic interests	0			0			0			22,222			(22,222)
Distributions to unitholders	(145,124)			0			(28,500)			(113,584)			(3,040)
Unit-based compensation	8,171			0			0			8,171			0
Tax withholdings on vested SMLP LTIP awards	(2,614)			0			0			(2,614)			0
DPPO partial settlement	51,750			0			0			51,750			0
Ending balance at Dec. 31, 2019	$ 763,516			$ 0			$ 293,616			$ 469,900			$ 0

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) - Gathering Services and Related Fees $ in Thousands	Dec. 31, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 122,055
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 102,127
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 84,736
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 66,693
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 50,608
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period
Revenue, remaining performance obligation	$ 59,602

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees Parenthetical (Details) - USD ($)
$ in Thousands

11 Months Ended

12 Months Ended

Nov. 30, 2019

^[1]

Nov. 30, 2018

^[1]

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Schedule Of Equity Method Investments [Line Items]

Impairment loss

$ 337,851

$ 10,888

$ 2,223

OGC | Summit Midstream Partners, LLC

Schedule Of Equity Method Investments [Line Items]

Impairment loss

$ 232,521

$ 5,652

329,700

$ 7,700

Write-off basis difference

(103,500)

OCC | Summit Midstream Partners, LLC

Schedule Of Equity Method Investments [Line Items]

Impairment loss

$ 6,300

[1]

(1)

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

1. ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

Organization. SMLP, a Delaware limited partnership, was formed in May 2012 and began operations in October 2012. SMLP is a growth-oriented limited partnership focused on developing, owning and operating midstream energy infrastructure assets that are strategically located in unconventional resource basins, primarily shale formations, in the continental United States. Our business activities are conducted through various operating subsidiaries, each of which is owned or controlled by our wholly owned subsidiary holding company, Summit Holdings, a Delaware limited liability company. References to the "Partnership," "we," or "our" refer collectively to SMLP and its subsidiaries.

The General Partner, a Delaware limited liability company, manages our operations and activities. Summit Investments, a Delaware limited liability company, is the ultimate owner of our General Partner and has the right to appoint the entire Board of Directors. Summit Investments is controlled by Energy Capital Partners.

Summit Investments owned an approximate 2% general partner interest in SMLP (including the IDRs) until March 22, 2019. On March 22, 2019, we executed an equity restructuring agreement with the General Partner and SMP Holdings pursuant to which the IDRs and the 2% general partner interest were converted into a non-economic general partner interest in exchange for 8,750,000 common units which were issued to SMP Holdings (the “Equity Restructuring”). As of December 31, 2019, SMP Holdings, a wholly owned subsidiary of Summit Investments, beneficially owned 45,318,866 SMLP common units and a subsidiary of Energy Capital Partners directly owned 5,915,827 SMLP common units.

Neither SMLP nor its subsidiaries have any employees. All of the personnel that conduct our business are employed by Summit Investments, but these individuals are sometimes referred to as our employees.

Business Operations. We provide natural gas gathering, compression, treating and processing services as well as crude oil and produced water gathering services pursuant to primarily long-term, fee-based agreements with our customers. Our results are primarily driven by the volumes of natural gas that we gather, compress, treat and/or process as well as by the volumes of crude oil and produced water that we gather. We are the owner-operator of, or have significant ownership interests in, the following gathering and transportation systems:

•

Summit Utica, a natural gas gathering system operating in the Appalachian Basin, which includes the Utica and Point Pleasant shale formations in southeastern Ohio;

•

Ohio Gathering, a natural gas gathering system and a condensate stabilization facility operating in the Appalachian Basin, which includes the Utica and Point Pleasant shale formations in southeastern Ohio;

•

Polar and Divide, a crude oil and produced water gathering system and transmission pipeline operating in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota;

•

Bison Midstream, an associated natural gas gathering system operating in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota;

•

Niobrara G&P, an associated natural gas gathering and processing system operating in the DJ Basin, which includes the Niobrara and Codell shale formations in northeastern Colorado and southeastern Wyoming;

•

Summit Permian, an associated natural gas gathering and processing system operating in the northern Delaware Basin, which includes the Wolfcamp and Bone Spring formations, in southeastern New Mexico;

•

Double E, a 1.35 Bcf/d natural gas transmission pipeline that is under development and will provide transportation service from multiple receipt points in the Delaware Basin to various delivery points in and around the Waha Hub in Texas;

•

Grand River, a natural gas gathering and processing system operating in the Piceance Basin, which includes the Mesaverde formation and the Mancos and Niobrara shale formations in western Colorado;

•

DFW Midstream, a natural gas gathering system operating in the Fort Worth Basin, which includes the Barnett Shale formation in north-central Texas; and

•

Mountaineer Midstream, a natural gas gathering system operating in the Appalachian Basin, which includes the Marcellus Shale formation in northern West Virginia.

Until March 22, 2019, we owned Tioga Midstream, a crude oil, produced water and associated natural gas gathering system operating in the Williston Basin. Refer to Note 17 for details on the sale of Tioga Midstream.

In June 2019, in conjunction with the Double E Project, Summit Permian Transmission entered into a definitive joint venture agreement (the “Agreement”) with an affiliate of Double E’s foundation shipper (the “JV Partner”) to fund the capital expenditures associated with the Double E Project. Refer to Note 8 for additional details.

Other than our investments in Double E and Ohio Gathering, all of our business activities are conducted through wholly owned operating subsidiaries.

Presentation and Consolidation. We prepare our consolidated financial statements in accordance with GAAP as established by the FASB. We make estimates and assumptions that affect the reported amounts of assets and liabilities at the balance sheet dates, including fair value measurements, the reported amounts of revenues and expenses and the disclosure of commitments and contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates.

The consolidated financial statements include the assets, liabilities and results of operations of SMLP and its subsidiaries. All intercompany transactions among the consolidated entities have been eliminated in consolidation. Comprehensive income or loss is the same as net income or loss for all periods presented.

AMORTIZING INTANGIBLE ASSETS - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Revenue \| Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (1,220)	$ (1,555)	$ (1,555)
Costs And Expenses \| Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	25,587	26,141	34,202
Costs And Expenses \| Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 6,278	$ 6,448	$ 6,153

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - SMP Holdings	Dec. 31, 2019	Dec. 31, 2018
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	4.55%	5.03%
Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Stated interest rate	5.75%	5.75%

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)					1 Months Ended		10 Months Ended	12 Months Ended
	Mar. 31, 2020	Nov. 15, 2019	Nov. 07, 2019	Mar. 22, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Summary of Significant Accounting Policies [Line Items]
Goodwill impairment					$ 16,200,000			$ 16,211,000	$ 0	$ 0
Goodwill								$ 0	$ 16,211,000
Long-term, fee-based contracts with original terms								up to 25 years
Right-of-use asset								$ 3,580,000
Accounting Standard Update 2016-02
Summary of Significant Accounting Policies [Line Items]
Right-of-use asset											$ 5,400,000
Operating Lease, Liability											$ 5,400,000
General Partner \| Summit Midstream Partners, LP
Summary of Significant Accounting Policies [Line Items]
General partner interest				2.00%				2.00%
Drop Down Assets 2016 Acquisition
Summary of Significant Accounting Policies [Line Items]
Payments to Acquire Businesses, Gross		$ 51,750,000	$ 51,750,000
Business acquisition, reduced amount of consideration			19,250,000
Remaining cash consideration payable			$ 180,750,000				$ 303,500,000
Remaining consideration description			the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020			Remaining Consideration at $303.5 million, with such amount to be paid by the Partnership in one or more payments over the period from March 1, 2020 through December 31, 2020, in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, at the discretion of the Partnership. At least 50% of the Remaining Consideration must be paid on or before June 30, 2020 and interest will accrue at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020		the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest will accrue (and will be payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020
Drop Down Assets 2016 Acquisition \| Scenario Forecast
Summary of Significant Accounting Policies [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%						8.00%
Drop Down Assets 2016 Acquisition \| Common units
Summary of Significant Accounting Policies [Line Items]
Business acquisition, share issued (shares)		10,714,285	10,714,285
Favorable gas gathering contracts \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								10 years
Favorable gas gathering contracts \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								20 years
Other Gas Gathering Contract \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								3 years
Other Gas Gathering Contract \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								25 years
Rights-of-way \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								20 years
Rights-of-way \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)								30 years

EQUITY METHOD INVESTMENTS

12 Months Ended

Dec. 31, 2019

Equity Method Investments And Joint Ventures [Abstract]

EQUITY METHOD INVESTMENTS

8. EQUITY METHOD INVESTMENTS

Double E

In June 2019, we formed Double E in connection with the Double E Project. Effective June 26, 2019, Summit Permian Transmission, a wholly owned and consolidated subsidiary of the Partnership, and our JV Partner executed the Agreement whereby Double E will provide natural gas transportation services from multiple receipt points in the Delaware Basin to various delivery points in and around the Waha Hub in Texas. In connection with the Agreement and the related Double E Project, the Partnership contributed total assets of approximately $23.6 million in exchange for a 70% ownership interest in Double E and our JV Partner contributed $7.3 million of cash in exchange for a 30% ownership interest in Double E. Concurrent with these contributions, and in accordance with the Agreement, Double E

distributed $7.3 million to the Partnership. Subsequent to the formation of Double E, we also made additional cash investments of $18.3 million through December 2019.

Double E is deemed to be a variable interest entity as defined in GAAP. As of the date of the Agreement, Summit Permian Transmission was not deemed to be the primary beneficiary due to the JV Partner’s voting rights on significant matters. We account for our ownership interest in Double E as an equity method investment because we have significant influence over Double E. Our portion of Double E’s net assets, which was $34.7 million at December 31, 2019, is reported under the caption Investment in equity method investees on the consolidated balance sheet.

For the year ended December 31, 2019, other than the investment activity noted above, Double E did not have any results of operations given that the Double E Project is currently under development.

Ohio Gathering

Ohio Gathering owns, operates and is currently developing midstream infrastructure consisting of a liquids-rich natural gas gathering system, a dry natural gas gathering system and a condensate stabilization facility in the Utica Shale in southeastern Ohio. Ohio Gathering provides gathering services pursuant to primarily long-term, fee-based gathering agreements, which include acreage dedications.

Our initial investment in Ohio Gathering in 2014 included a $190.0 million payment to acquire a 1% interest from a third party, which included an option to increase our ownership to 40%, as well as a series of contributions directly to Ohio Gathering in 2014, which increased our ownership to 40%. Concurrent with and subsequent to the exercise of the option, the non-affiliated owners have retained their respective 60% ownership interest in Ohio Gathering (the "Non-affiliated Owners").

We account for our ownership interests in Ohio Gathering as an equity method investment because we have joint control with the Non-affiliated Owners, which gives us significant influence.

We recognized the $190.0 million paid for the initial 1% interest as an investment in Ohio Gathering at inception. In addition, Ohio Gathering assigned a value of $7.5 million to the exercise option, which it ultimately attributed to our capital account. Neither of the aforementioned transactions involved a flow of funds to or from Ohio Gathering. As such, they created a basis difference between our recorded investment in equity method investees and the amount attributed to us by Ohio Gathering within its financial statements.

In December 2019, we identified certain triggering events which indicated that our equity method investment in Ohio Gathering could be impaired. In accordance with ASC Topic 323, we completed an equity method impairment analysis to determine the equity method impairment charge to be recorded on our consolidated financial statements resulting from an other-than-temporary impairment. As a result of our analysis, an impairment charge of approximately $329.7 million was recorded in 2019 in Loss from equity method investments on the accompanying consolidated statements of operations.

The fair value of our investment in Ohio Gathering was determined based upon applying the discounted cash flow method, which is an income approach, and the guideline public company method, which is a market approach. The discounted cash flow fair value estimate is based on known or knowable information at the measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future results using a probability weighted average set of cash flow forecasts and a discount rate of approximately 9.0 percent. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of the Ohio Gathering equity method investment represents a Level 3 measurement. As a result, actual results may differ from the estimates and assumptions made for purposes of this impairment analysis.

Also in December 2019, an impairment loss of long-lived assets was recognized by OCC. Although we recognize activity for Ohio Gathering on a one-month lag, we recorded an impairment loss of $6.3 million in Loss from equity method investees in the consolidated statements of operations because the information was available to us.

In December 2018, Ohio Gathering was involved in legal proceedings relating to a dispute regarding pipeline right of way rights and associated trespass claims that took place prior to December 31, 2018. Ohio Gathering received a judgment on those proceedings in January 2019 and recorded an estimate of the legal exposure as of December 31, 2018. Although we recognize activity for Ohio Gathering on a one-month lag, we recorded the asset impairments and legal contingency in our results of operations for the year ending December 31, 2018 because the information was available to us. We recorded our then 40% share of the asset impairments and legal contingency amounting to $7.7 million in 2018 in Loss from equity method investees in the consolidated statements of operations.

As a result of our joint venture partner funding a disproportionate amount of the capital calls during the year ended December 31, 2019, our ownership interest in Ohio Gathering decreased from 40.0% at December 31, 2018, to 38.5% at December 31, 2019.

	2019		2018
	(In thousands)
Investment in Ohio Gathering, December 31	$	275,000	$	649,250
December cash distributions		2,700		2,736
Impairment loss (1)		232,521		5,652
Loss contingency		—		2,040
Basis difference		—		(116,832	)
Investment in Ohio Gathering, net of basis difference, November 30	$	510,221	$	542,846

(1)

Summarized balance sheet information for OGC and OCC follows (amounts represent 100% of investee financial information).

	November 30, 2019				November 30, 2018
	OGC		OCC		OGC		OCC
	(In thousands)
Current assets	$	41,972	$	2,187	$	37,403	$	3,716
Noncurrent assets		1,281,171		28,323		1,262,253		27,203
Total assets	$	1,323,143	$	30,510	$	1,299,656	$	30,919

Current liabilities	$	21,798	$	4,016	$	19,903	$	3,912
Noncurrent liabilities		4,113		6,683		3,688		8,807
Total liabilities	$	25,911	$	10,699	$	23,591	$	12,719

Summarized statements of operations information for OGC and OCC follow (amounts represent 100% of investee financial information).

	Twelve months ended November 30, 2019					Twelve months ended November 30, 2018				Twelve months ended November 30, 2017
	OGC		OCC			OGC		OCC		OGC		OCC
	(In thousands)
Total revenues	$	142,138	$	8,601		$	142,398	$	10,177	$	140,679	$	8,607
Total operating expenses		108,234		38,815			136,722		9,053		111,897		8,298
Net income (loss)		33,897		(30,214	)		5,670		498		28,785		(907	)

AMORTIZING INTANGIBLE ASSETS - Intangible Assets and Liabilities Subject to Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 459,818	$ 468,852
Accumulated amortization	(227,540)	(195,436)
Net	232,278	273,416
Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24,195	24,195
Accumulated amortization	(15,125)	(13,905)
Net	9,070	10,290
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	278,448	278,448
Accumulated amortization	(169,549)	(143,962)
Net	108,899	134,486
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	157,175	166,209
Accumulated amortization	(42,866)	(37,569)
Net	$ 114,309	$ 128,640

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Carrying value \| 5.5% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 298,314	$ 297,638
Carrying value \| 5.75% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	494,985	494,093
Fair Value \| 5.5% Senior Notes \| Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	266,750	286,625
Fair Value \| 5.75% Senior Notes \| Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 382,708	$ 455,208

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 1.4375	$ 2.300	$ 2.300

DEBT - Senior Notes (Narrative) (Details) - USD ($)		1 Months Ended
DEBT - Senior Notes (Narrative) (Details) - USD ($)	Jul. 31, 2014	Nov. 30, 2018	Feb. 28, 2017	Jul. 31, 2014	Jun. 30, 2013	Dec. 31, 2019	Feb. 08, 2017
Revolving credit facility
Debt Instrument [Line Items]
Extinguishment of debt			$ 172,000,000.0
Guarantor Subsidiaries
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary		100.00%
5.75% Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%			5.75%
Unsecured notes			$ 500,000,000.0
Deferred issuance costs							$ 7,700
Default period			30 days
Compliance notice period			30 days
Final judgment			$ 75,000,000.0
Percent of principal (at least)			25.00%
5.75% Senior Notes \| Redemption period one
Debt Instrument [Line Items]
Percent of principal redeemed			35.00%
Redemption price, expressed as percentage of principal amount			105.75%
5.75% Senior Notes \| Redemption period two
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount			104.313%
5.75% Senior Notes \| Redemption period three
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount			100.00%
5.5% Senior Notes
Debt Instrument [Line Items]
Stated interest rate						5.50%
Debt issuance costs	$ 5,100,000			$ 5,100,000
Events of default, period of payment default				30 days
Events of default, failure to comply with covenants, period after notice				180 days
Events of default, failure to comply with other agreements in the indenture, period after notice				30 days
Events of default, failure to pay final judgments, in excess of 20.0 million				$ 20,000,000.0
Declaration of immediate payment, holding percent of principal amount required				25.00%
Summit Holdings and Finance Corporation \| Senior Notes Due August 2022
Debt Instrument [Line Items]
Senior unsecured notes	$ 300,000,000.0			$ 300,000,000.0
Stated interest rate	5.50%			5.50%
Maturity date	Aug. 15, 2022
Summit Holdings and Finance Corporation \| 7.5% Senior Notes
Debt Instrument [Line Items]
Unsecured notes			$ 300,000,000.0
Redemption and call premiums			$ 17,900,000
Summit Holdings and Finance Corporation \| 5.5% Senior Notes \| Redemption period one
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount				101.375%
Summit Holdings and Finance Corporation \| 5.5% Senior Notes \| Redemption period two
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount				100.00%
Subsidiary of Summit Investments \| Summit Midstream OpCo, LP
Debt Instrument [Line Items]
Ownership interest		1.00%
Finance Corp \| Summit Holdings
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary					100.00%

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Cash Flow Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$ 182,337	$ 227,929	$ 237,832
Cash flows from investing activities:
Capital expenditures	(182,291)	(200,586)	(124,215)
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)	102,111	496	2,300
Distributions from equity method investment	7,313	0	0
Investment in equity method investee	(18,316)	0	0
Contributions to equity method investees	0	(4,924)	(25,513)
Purchase of noncontrolling interest	0	(10,981)	(797)
Other, net	313	(284)	(458)
Net cash used in investing activities	(90,870)	(216,279)	(148,683)
Cash flows from financing activities:
Distributions to unitholders	(116,624)	(180,705)	(179,103)
Borrowings under Revolving Credit Facility	369,000	289,000	247,500
Repayments under Revolving Credit Facility	(158,000)	(84,000)	(634,500)
Repayment of Deferred Purchase Price Obligation	(151,750)	0	0
Debt issuance costs	(499)	(344)	(16,390)
Payment of redemption and call premiums on senior notes	0	0	(17,932)
Proceeds from ATM Program common unit issuances, net of costs	0	0	17,078
Proceeds from issuance of Series A Preferred Units, net of costs	27,392	0	293,238
Contribution from General Partner	0	0	465
Issuance of senior notes	0	0	500,000
Tender and redemption of senior notes	0	0	(300,000)
Other, net	(4,491)	(4,186)	(3,128)
Net cash used in financing activities	(63,472)	(8,735)	(95,147)
Net change in cash, cash equivalents and restricted cash	27,995	2,915	(5,998)
Cash and cash equivalents, beginning of period	4,345	1,430	7,428
Cash and cash equivalents, end of period	32,340	4,345	1,430
Consolidation Adjustments
Cash flows from investing activities:
Advances to affiliates	352,175	233,919	426,722
Net cash used in investing activities	352,175	233,919	426,722
Cash flows from financing activities:
Advances from affiliates	(352,175)	(233,919)	(426,722)
Net cash used in financing activities	(352,175)	(233,919)	(426,722)
Series A Preferred Units
Cash flows from financing activities:
Distributions to unitholders	(28,500)	(28,500)	(2,375)
SMLP
Cash flows from operating activities:
Net cash provided by (used in) operating activities	5,811	7,470	7,122
Cash flows from investing activities:
Capital expenditures	(1,323)	(3,323)	(3,041)
Purchase of noncontrolling interest		(10,981)	(797)
Other, net	314	(284)	(458)
Advances to affiliates	(28,776)	(7,312)	(278,493)
Net cash used in investing activities	(29,785)	(21,900)	(282,789)
Cash flows from financing activities:
Distributions to unitholders	(116,624)	(180,705)	(179,103)
Repayment of Deferred Purchase Price Obligation	(151,750)
Proceeds from ATM Program common unit issuances, net of costs			17,078
Proceeds from issuance of Series A Preferred Units, net of costs			293,238
Contribution from General Partner			465
Other, net	(2,618)	(2,913)	(2,437)
Advances from affiliates	323,399	226,607	148,229
Net cash used in financing activities	23,907	14,489	275,095
Net change in cash, cash equivalents and restricted cash	(67)	59	(572)
Cash and cash equivalents, beginning of period	185	126	698
Cash and cash equivalents, end of period	118	185	126
SMLP \| Series A Preferred Units
Cash flows from financing activities:
Distributions to unitholders	(28,500)	(28,500)	(2,375)
Co-Issuers
Cash flows from operating activities:
Net cash provided by (used in) operating activities	(69,891)	(56,181)	(68,915)
Cash flows from investing activities:
Advances to affiliates	(140,229)	(148,320)
Net cash used in investing activities	(140,229)	(148,320)
Cash flows from financing activities:
Borrowings under Revolving Credit Facility	369,000	289,000	247,500
Repayments under Revolving Credit Facility	(158,000)	(84,000)	(634,500)
Debt issuance costs	(499)	(344)	(16,390)
Payment of redemption and call premiums on senior notes			(17,932)
Issuance of senior notes			500,000
Tender and redemption of senior notes			(300,000)
Advances from affiliates			290,261
Net cash used in financing activities	210,501	204,656	68,939
Net change in cash, cash equivalents and restricted cash	381	155	24
Cash and cash equivalents, beginning of period	230	75	51
Cash and cash equivalents, end of period	611	230	75
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities	246,492	276,640	299,625
Cash flows from investing activities:
Capital expenditures	(163,379)	(189,951)	(121,174)
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)	102,111	496	2,300
Contributions to equity method investees		(4,924)	(25,513)
Other, net	(1)
Advances to affiliates	(183,170)	(78,287)	(148,229)
Net cash used in investing activities	(244,439)	(272,666)	(292,616)
Cash flows from financing activities:
Other, net	(1,873)	(1,273)	(691)
Advances from affiliates			(11,768)
Net cash used in financing activities	(1,873)	(1,273)	(12,459)
Net change in cash, cash equivalents and restricted cash	180	2,701	(5,450)
Cash and cash equivalents, beginning of period	3,930	1,229	6,679
Cash and cash equivalents, end of period	4,110	3,930	$ 1,229
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities	(75)
Cash flows from investing activities:
Capital expenditures	(17,589)	(7,312)
Distributions from equity method investment	7,313
Investment in equity method investee	(18,316)
Net cash used in investing activities	(28,592)	(7,312)
Cash flows from financing activities:
Proceeds from issuance of Series A Preferred Units, net of costs	27,392
Advances from affiliates	28,776	7,312
Net cash used in financing activities	56,168	$ 7,312
Net change in cash, cash equivalents and restricted cash	27,501
Cash and cash equivalents, end of period	$ 27,501

REVENUE - Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenues	$ 112,247	$ 100,187	$ 99,686	$ 131,408	$ 133,671	$ 127,479	$ 128,183	$ 117,320	$ 443,528	$ 506,653	$ 488,741
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues									27,622	78,161
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues									415,906	428,492	469,224
Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues									33,991	35,233	38,907
Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues									105,651	123,650	161,503
Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues									26,050	15,294	11,860
Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues									133,638	155,519	154,893
Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues									20,303	958
Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues									71,802	68,265	71,667
Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues									24,471	29,573	$ 30,394
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues									326,747	344,616
Gathering Services and Related Fees \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues									(2,045)	(6,002)
Gathering Services and Related Fees \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues									328,792	350,618
Gathering Services and Related Fees \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues									31,926	35,233
Gathering Services and Related Fees \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues									77,626	79,606
Gathering Services and Related Fees \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues									21,940	11,251
Gathering Services and Related Fees \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues									121,357	135,810
Gathering Services and Related Fees \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues									3,610	115
Gathering Services and Related Fees \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues									47,862	59,030
Gathering Services and Related Fees \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues									24,471	29,573
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues									86,994	134,834
Natural Gas, NGLs and Condensate Sales \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues									28,660	84,457
Natural Gas, NGLs and Condensate Sales \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues									58,334	50,377
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues									0
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues									16,461	31,840
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues									389	371
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues									7,954	14,800
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues									16,383	843
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues									17,147	2,523
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues									0
Other Revenues
Disaggregation Of Revenue [Line Items]
Total revenues									29,787	27,203
Other Revenues \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues									1,007	(294)
Other Revenues \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues									28,780	27,497
Other Revenues \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues									2,065
Other Revenues \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues									11,564	12,204
Other Revenues \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues									3,721	3,672
Other Revenues \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues									4,327	4,909
Other Revenues \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues									310
Other Revenues \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues									6,793	$ 6,712
Other Revenues \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues									$ 0

GOODWILL - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
GOODWILL - Narrative (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill		$ 0	$ 16,211,000
Goodwill impairment	$ 16,200,000	16,211,000	0	$ 0
Mountaineer Midstream
Goodwill [Line Items]
Goodwill			$ 16,200,000
Goodwill impairment		$ 16,200,000

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING

17. DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING

Red Rock Gathering Asset Disposition. In December 2019, Red Rock Gathering and certain affiliates of SMLP (collectively, “the Red Rock Parties”) entered into a Purchase and Sale Agreement (the “Red Rock PSA”) pursuant to which the Red Rock Parties agreed to sell certain Red Rock Gathering system assets for a cash purchase price of $12.0 million, subject to adjustments as provided in the Red Rock PSA (the “Red Rock Sale”). Prior to closing, we recorded an impairment charge of $14.2 million based on the expected consideration and the carrying value for the Red Rock Gathering system assets. On December 2, 2019, we closed the Red Rock Sale. The impairment is included in the Long-lived asset impairment caption on the consolidated statement of operations. The financial contribution of these assets (a component of the Piceance Basin reportable segment) are included in our consolidated financial statements and footnotes for the period from January 1, 2019 through December 1, 2019.

Tioga Midstream Disposition. In February 2019, Tioga Midstream, LLC, a subsidiary of SMLP, and certain affiliates of SMLP (collectively, “the Tioga Parties”) entered into two Purchase and Sale Agreements (the “Tioga PSAs”) with Hess Infrastructure Partners LP and Hess North Dakota Pipelines LLC (collectively, “Hess Infrastructure”), pursuant to which the Tioga Parties agreed to sell the Tioga Midstream system to Hess Infrastructure for a combined cash purchase price of $90 million, subject to adjustments as provided in the Tioga PSAs (the “Tioga Midstream Sale”). On March 22, 2019, the Tioga Parties closed the Tioga Midstream Sale and recorded a gain on sale of $0.9 million based on the difference between the consideration received and the carrying value for Tioga Midstream at closing. The gain is included in the Gain on asset sales, net caption on the consolidated statement of operations. The financial results of Tioga Midstream (a component of the Williston Basin reportable segment) are included in our consolidated financial statements and footnotes through March 22, 2019.

2016 Drop Down. In 2016, SMLP acquired a controlling interest in OpCo, the entity which owns the 2016 Drop Down Assets. These assets include certain natural gas, crude oil and produced water gathering systems located in the Utica Shale, the Williston Basin and the DJ Basin, as well as ownership interests in Ohio Gathering.

The net consideration paid and recognized in connection with the 2016 Drop Down (i) consisted of a cash payment to SMP Holdings of $360.0 million funded with borrowings under our Revolving Credit Facility and a $0.6 million working capital adjustment received in June 2016 (the “Initial Payment”) and (ii) includes the Deferred Purchase Price Obligation payment due in 2020.

In March 2019, the Partnership amended the Contribution Agreement related to the 2016 Drop Down and fixed the Remaining Consideration at $303.5 million, with such amount to be paid by the Partnership in one or more payments over the period from March 1, 2020 through December 31, 2020, in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, at the discretion of the Partnership. At least 50% of the Remaining Consideration must be paid on or before June 30, 2020 and interest will accrue at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020.

On November 7, 2019, we and SMP Holdings entered into a second amendment (the “Second Amendment”) to the Contribution Agreement between us and SMP Holdings dated February 25, 2016, as amended. On November 15, 2019, we made a cash payment of $51.75 million and issued 10,714,285 common units to SMP Holdings (the “November 2019 Prepayment”). In addition, the parties reduced the Remaining Consideration due to SMP Holdings by $19.25 million. Following the November 2019 Prepayment, the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020. The form(s) of Remaining Consideration to be delivered by us to SMP Holdings continue to be determinable by us in our sole discretion.

The present value of the Deferred Purchase Price Obligation is reflected as a liability on our balance sheet until paid. As of December 31, 2019, the Remaining Consideration, which reflects the net present value of the $180.75 million Deferred Purchase Price Obligation, was $178.5 million on the consolidated balance sheet using a discount rate of 5.25%.

Restructuring Activities. In 2019, our management approved and initiated a plan to restructure our operations resulting in certain management, facility and organizational changes. During the year ended December 31, 2019, we expensed costs of approximately $5.0 million associated with restructuring activities. These activities consisted primarily of employee-related costs and consulting costs in support of the project. These costs are included within the General and administrative caption on the consolidated statement of operations.

As of December 31, 2019, the components of our restructuring plan are as follows:

•

Employee-related costs — we reorganized our workforce and eliminated redundant or unneeded positions. In connection with the workforce restructuring, we expect to incur severance, benefits and other employee related costs of approximately $6.0 million to be incurred over the twelve months following December 31, 2019. During the fiscal year ended December 31, 2019, we expensed approximately $3.8 million primarily related to severance, redundant salaries, certain bonuses and other employee benefits in connection with our plan. As of December 31, 2019, we had approximately $2.7 million included in current liabilities for these costs.

•

Consultants — we engaged third-party consulting firms to assist in the evaluation of the Company’s cost structure, to help formulate the plan to implement the project, and to provide project management services for certain project initiatives. During the fiscal year ended December 31, 2019, we expensed approximately $1.2 million related to these services. As of December 31, 2019, we had approximately $0.6 million included in current liabilities for these costs. We expect to incur an additional $0.2 million related to consulting costs to be incurred over the next twelve months following December 31, 2019.

CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)

12 Months Ended

Dec. 31, 2019

Condensed Consolidating Financial Information [Abstract]

Condensed Balance Sheet

Balance sheets as of December 31, 2019 and 2018 follow.

	December 31, 2019
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	118	$	611	$	4,110	$	109	$	—		$	4,948
Restricted cash		—		—		—		27,392		—			27,392
Accounts receivable		69		—		102,049		—		—			102,118
Other current assets		2,124		—		2,894		—		—			5,018
Due from affiliate		—		36,300		776,552		—		(812,852	)		—
Total current assets		2,311		36,911		885,605		27,501		(812,852	)		139,476
Property, plant and equipment, net		6,420		—		1,875,558		—		273			1,882,251
Intangible assets, net		—		—		232,278		—		—			232,278
Investment in equity method investees		—		—		275,000		35,002		(274	)		309,728
Other noncurrent assets		3,152		6,167		29		370		—			9,718
Investment in subsidiaries		1,758,547		3,198,079		—		—		(4,956,626	)		—
Total assets	$	1,770,430	$	3,241,157	$	3,268,470	$	62,873	$	(5,769,479	)	$	2,573,451

Liabilities and Capital
Trade accounts payable	$	657	$	—	$	23,758	$	—	$	—		$	24,415
Accrued expenses		1,649		—		9,536		297		—			11,482
Due to affiliate		777,077		—		—		—		(776,766	)		311
Deferred revenue		—		—		13,493		—		—			13,493
Ad valorem taxes payable		14		—		8,463				—			8,477
Accrued interest		—		12,311		—		—		—			12,311
Accrued environmental remediation		—		—		1,725		—		—			1,725
Other current liabilities		7,342		—		4,591				—			11,933
Total current liabilities		786,739		12,311		61,566		297		(776,766	)		84,147
Long-term debt		—		1,470,299		—		—		—			1,470,299
Noncurrent Deferred Purchase Price Obligation		178,453		—		—		—		—			178,453
Noncurrent deferred revenue		—		—		38,709		—		—			38,709
Noncurrent accrued environmental remediation		—		—		2,926		—		—			2,926
Other noncurrent liabilities		5,635		—		2,316		—		—			7,951
Total liabilities		970,827		1,482,610		105,517		297		(776,766	)		1,782,485

Total mezzanine capital		—		—		—		27,450		—			27,450

Total partners' capital		799,603		1,758,547		3,162,953		35,126		(4,992,713	)		763,516
Total liabilities, mezzanine capital and partners' capital	$	1,770,430	$	3,241,157	$	3,268,470	$	62,873	$	(5,769,479	)	$	2,573,451

	December 31, 2018
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	185	$	230	$	3,930	$	—	$	—		$	4,345
Accounts receivable		321		—		97,615		—		—			97,936
Other current assets		1,179		—		2,792		—		—			3,971
Due from affiliate		—		—		593,384		—		(593,384	)		—
Total current assets		1,685		230		697,721		—		(593,384	)		106,252
Property, plant and equipment, net		5,813		—		1,948,280		9,620		—			1,963,713
Intangible assets, net		—		—		273,416		—		—			273,416
Goodwill		—		—		16,211		—		—			16,211
Investment in equity method investees		—		—		649,250		—		—			649,250
Other noncurrent assets		3,183		8,511		26		—		—			11,720
Investment in subsidiaries		2,096,717		3,461,921		—		—		(5,558,638	)		—
Total assets	$	2,107,398	$	3,470,662	$	3,584,904	$	9,620	$	(6,152,022	)	$	3,020,562

Liabilities and Partners' Capital
Trade accounts payable	$	275	$	—	$	35,831	$	2,308	$	—		$	38,414
Accrued expenses		1,106		—		20,857		—		—			21,963
Due to affiliate		482,384		103,928		—		—		(586,072	)		240
Deferred revenue		—		—		11,467		—		—			11,467
Ad valorem taxes payable		14		—		10,536		—		—			10,550
Accrued interest		—		12,286		—		—		—			12,286
Accrued environmental remediation		—		—		2,487		—		—			2,487
Other current liabilities		7,306		—		5,339		—		—			12,645
Total current liabilities		491,085		116,214		86,517		2,308		(586,072	)		110,052
Long-term debt		—		1,257,731		—		—		—			1,257,731
Noncurrent Deferred Purchase Price Obligation		383,934		—		—		—		—			383,934
Noncurrent deferred revenue		—		—		39,504		—		—			39,504
Noncurrent accrued environmental remediation		—		—		3,149		—		—			3,149
Other noncurrent liabilities		3,843		—		1,125		—		—			4,968
Total liabilities		878,862		1,373,945		130,295		2,308		(586,072	)		1,799,338

Total partners' capital		1,228,536		2,096,717		3,454,609		7,312		(5,565,950	)		1,221,224
Total liabilities partners' capital	$	2,107,398	$	3,470,662	$	3,584,904	$	9,620	$	(6,152,022	)	$	3,020,562

Condensed Income Statement

Statements of operation for the years ended December 31, 2019, 2018 and 2017 follow.

	Year ended December 31, 2019
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments		Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	326,747					$	—	$	326,747
Natural gas, NGLs and condensate sales		—			—			86,994			—			—		86,994
Other revenues		—			—			29,787						—		29,787
Total revenues		—			—			443,528			—			—		443,528
Costs and expenses:
Cost of natural gas and NGLs		—			—			63,438			—			—		63,438
Operation and maintenance		—			—			97,587			—			—		97,587
General and administrative		—			—			54,139			—			—		54,139
Depreciation and amortization		2,604			—			107,602			—			—		110,206
Transaction costs		1,788			—			—			—			—		1,788
Loss (gain) on asset sales, net		9			—			(1,545	)		—			—		(1,536	)
Long-lived asset impairment		—			—			60,507			—			—		60,507
Goodwill impairment		—			—			16,211			—			—		16,211
Total costs and expenses		4,401			—			397,939			—			—		402,340
Other income		451			—			—			—			—		451
Interest expense		—			(74,327	)		(102	)		—			—		(74,429	)
Deferred Purchase Price Obligation		1,982			—			—			—			—		1,982
(Loss) income before income taxes and loss from equity method investees		(1,968	)		(74,327	)		45,487			—			—		(30,808	)
Income tax expense		(1,174	)		—			—			—			—		(1,174	)
Loss from equity method investees		—			—			(336,950	)		(901	)		—		(337,851	)
Equity in earnings of consolidated subsidiaries		(366,691	)		(292,364	)		—			—			659,055		—
Net (loss) income	$	(369,833	)	$	(366,691	)	$	(291,463	)	$	(901	)	$	659,055	$	(369,833	)

	Year ended December 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	344,616		$	—	$	—		$	344,616
Natural gas, NGLs and condensate sales		—			—			134,834			—		—			134,834
Other revenues		—			—			27,203			—		—			27,203
Total revenues		—			—			506,653			—		—			506,653
Costs and expenses:
Cost of natural gas and NGLs		—			—			107,661			—		—			107,661
Operation and maintenance		—			—			96,878			—		—			96,878
General and administrative		—			—			52,877			—		—			52,877
Depreciation and amortization		1,743			—			105,357			—		—			107,100
Long-lived asset impairment		—			—			7,186			—		—			7,186
Total costs and expenses		1,743			—			369,959			—		—			371,702
Other income		(169	)		—			—			—		—			(169	)
Interest expense		—			(60,442	)		(93	)		—		—			(60,535	)
Deferred Purchase Price Obligation		(20,975	)		—			—			—		—			(20,975	)
Income (loss) before income taxes and loss from equity method investees		(22,887	)		(60,442	)		136,601			—		—			53,272
Income tax expense		(33	)		—			—			—		—			(33	)
Loss from equity method investees		—			—			(10,888	)		—		—			(10,888	)
Equity in earnings of consolidated subsidiaries		65,271			125,713			—			—		(190,984	)		—
Net income	$	42,351		$	65,271		$	125,713		$	—	$	(190,984	)	$	42,351

	Year ended December 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments		Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	394,427		$	—	$	—	$	394,427
Natural gas, NGLs and condensate sales		—			—			68,459			—		—		68,459
Other revenues		—			—			25,855			—		—		25,855
Total revenues		—			—			488,741			—		—		488,741
Costs and expenses:
Cost of natural gas and NGLs		—			—			57,237			—		—		57,237
Operation and maintenance		—			—			93,882			—		—		93,882
General and administrative		—			—			54,681			—		—		54,681
Depreciation and amortization		1,101			—			114,374			—		—		115,475
Transaction costs		73			—			—			—		—		73
Gain on asset sales, net		—			—			527			—		—		527
Long-lived asset impairment		—			—			188,702			—		—		188,702
Total costs and expenses		1,174			—			509,403			—		—		510,577
Other income		298			—			—			—		—		298
Interest expense		—			(68,080	)		(51	)		—		—		(68,131	)
Early extinguishment of debt		—			(22,039	)		—			—		—		(22,039	)
Deferred Purchase Price Obligation		200,322			—			—			—		—		200,322
Loss before income taxes and loss from equity method investees		199,446			(90,119	)		(20,713	)		—		—		88,614
Income tax expense		(341	)		—			—			—		—		(341	)
Loss from equity method investees		—			—			(2,223	)		—		—		(2,223	)
Equity in loss of consolidated subsidiaries		(113,055	)		(22,936	)		—			—		135,991		—
Net loss	$	86,050		$	(113,055	)	$	(22,936	)	$	—	$	135,991	$	86,050

Condensed Cash Flow Statement

Statement of cash flows for the years ended December 31, 2019, 2018 and 2017 follow.

	Year ended December 31, 2019
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	5,811		$	(69,891	)	$	246,492		$	(75	)	$	—		$	182,337

Cash flows from investing activities:
Capital expenditures		(1,323	)		—			(163,379	)		(17,589	)		—			(182,291	)
Proceeds from asset sales		—			—			102,111			—			—			102,111
Distributions from equity method investment		—			—			—			7,313			—			7,313
Investment in equity method investee		—			—			—			(18,316	)		—			(18,316	)
Other, net		314			—			(1	)		—			—			313
Advances to affiliates		(28,776	)		(140,229	)		(183,170	)		—			352,175			—
Net cash (used in) provided by investing activities		(29,785	)		(140,229	)		(244,439	)		(28,592	)		352,175			(90,870	)

Cash flows from financing activities:
Distributions to unitholders		(116,624	)		—			—			—			—			(116,624	)
Distributions to Series A Preferred unitholders		(28,500	)		—			—			—			—			(28,500	)
Borrowings under Revolving Credit Facility		—			369,000			—			—			—			369,000
Repayments under Revolving Credit Facility		—			(158,000	)		—			—			—			(158,000	)
Repayment of Deferred Purchase Price Obligation		(151,750	)		—			—			—			—			(151,750	)
Debt issuance costs		—			(499	)		—			—			—			(499	)
Proceeds from the issuance of Series A preferred units, net of costs		—			—			—			27,392			—			27,392
Other, net		(2,618	)		—			(1,873	)					—			(4,491	)
Advances from affiliates		323,399			—			—			28,776			(352,175	)		—
Net cash (used in) provided by financing activities		23,907			210,501			(1,873	)		56,168			(352,175	)		(63,472	)
Net change in cash, cash equivalents and restricted cash		(67	)		381			180			27,501			—			27,995
Cash, cash equivalents and restricted cash, beginning of period		185			230			3,930			—			—			4,345
Cash, cash equivalents and restricted cash, end of period	$	118		$	611		$	4,110		$	27,501		$	—		$	32,340

	Year ended December 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	7,470		$	(56,181	)	$	276,640		$	—		$	—		$	227,929

Cash flows from investing activities:
Capital expenditures		(3,323	)		—			(189,951	)		(7,312	)		—			(200,586	)
Proceeds from asset sales		—			—			496			—			—			496
Contributions to equity method investees		—			—			(4,924	)		—			—			(4,924	)
Purchase of noncontrolling interest		(10,981	)		—			—			—			—			(10,981	)
Other, net		(284	)		—			—			—			—			(284	)
Advances to affiliates		(7,312	)		(148,320	)		(78,287	)		—			233,919			—
Net cash provided by (used in) investing activities		(21,900	)		(148,320	)		(272,666	)		(7,312	)		233,919			(216,279	)

Cash flows from financing activities:
Distributions to unitholders		(180,705	)		—			—			—			—			(180,705	)
Distributions to Series A Preferred unitholders		(28,500	)		—			—			—			—			(28,500	)
Borrowings under Revolving Credit Facility		—			289,000			—			—			—			289,000
Repayments under Revolving Credit Facility		—			(84,000	)		—			—			—			(84,000	)
Debt issuance costs		—			(344	)		—			—			—			(344	)
Other, net		(2,913	)		—			(1,273	)		—			—			(4,186	)
Advances from affiliates		226,607			—			—			7,312			(233,919	)		—
Net cash (used in) provided by financing activities		14,489			204,656			(1,273	)		7,312			(233,919	)		(8,735	)
Net change in cash and cash equivalents		59			155			2,701			—			—			2,915
Cash and cash equivalents, beginning of period		126			75			1,229			—			—			1,430
Cash and cash equivalents, end of period	$	185		$	230		$	3,930		$	—		$	—		$	4,345

	Year ended December 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	7,122		$	(68,915	)	$	299,625		$	—	$	—		$	237,832

Cash flows from investing activities:
Capital expenditures		(3,041	)		—			(121,174	)		—		—			(124,215	)
Proceeds from asset sales		—			—			2,300			—		—			2,300
Contributions to equity method investees		—			—			(25,513	)		—		—			(25,513	)
Purchase of noncontrolling interest		(797	)		—			—			—		—			(797	)
Other, net		(458	)		—			—			—		—			(458	)
Advances to affiliates		(278,493	)		—			(148,229	)		—		426,722			—
Net cash used in investing activities		(282,789	)		—			(292,616	)		—		426,722			(148,683	)

Cash flows from financing activities:
Distributions to unitholders		(179,103	)		—			—			—		—			(179,103	)
Distributions to Series A Preferred unitholders		(2,375	)		—			—			—		—			(2,375	)
Borrowings under Revolving Credit Facility		—			247,500			—			—		—			247,500
Repayments under Revolving Credit Facility		—			(634,500	)		—			—		—			(634,500	)
Debt issuance costs		—			(16,390	)		—			—		—			(16,390	)
Payment of redemption and call premiums on senior notes		—			(17,932	)		—			—		—			(17,932	)
Proceeds from ATM Program issuances, net of costs		17,078			—			—			—		—			17,078
Proceeds from issuance of Series A preferred units, net of costs		293,238			—			—			—		—			293,238
Contribution from General Partner		465			—			—			—		—			465
Issuance of senior notes		—			500,000			—			—		—			500,000
Tender and redemption of senior notes		—			(300,000	)		—			—		—			(300,000	)
Other, net		(2,437	)		—			(691	)		—		—			(3,128	)
Advances from affiliates		148,229			290,261			(11,768	)		—		(426,722	)		—
Net cash provided by (used in) financing activities		275,095			68,939			(12,459	)		—		(426,722	)		(95,147	)
Net change in cash and cash equivalents		(572	)		24			(5,450	)		—		—			(5,998	)
Cash and cash equivalents, beginning of period		698			51			6,679			—		—			7,428
Cash and cash equivalents, end of period	$	126		$	75		$	1,229		$	—	$	—		$	1,430

AMORTIZING INTANGIBLE ASSETS - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Mar. 31, 2019
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Impairment charge for intangible assets			$ 0.5
Williston Basin \| Contract Intangible Assets and Rights-of-Way Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Impairment charge for intangible assets	$ 85.2
Permian Basin
Finite-Lived Intangible Assets [Line Items]
Impairment charge for intangible assets		$ 0.6

LEASES, COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

LEASES, COMMITMENTS AND CONTINGENCIES

16. LEASES, COMMITMENTS AND CONTINGENCIES

Leases. We account for leases in accordance with Topic 842, which we adopted on January 1, 2019, using the modified retrospective method. Under the modified retrospective method, the comparative information is not adjusted and is reported under the accounting standards in effect for those periods. See Note 2 for further discussion of the adoption.

We and Summit Investments lease certain office space and equipment under operating leases. We lease office space for our corporate headquarters as well as for corporate offices in Dallas, Denver and Atlanta and offices in and around our gathering systems for terms of between 3 and 10 years. We lease the office space to limit exposure to risks related to ownership, such as fluctuations in real estate prices. In addition, we lease equipment primarily to support our operations in response to the needs of our gathering systems for terms of between 3 and 4 years. We and Summit Investments also lease vehicles under finance leases to support our operations in response to the needs of our gathering systems for a term of 3 years. We only lease from reputable companies and our leased assets are not specialized in our industry.

Some of our leases are subject to annual escalations relating to the Consumer Price Index (“CPI”). While lease liabilities are not remeasured as a result of changes to the CPI, changes to the CPI are treated as variable lease payments and recognized in the period in which the obligation for those payments was incurred.

We have options to extend the lease term of certain office space in Texas, Colorado and West Virginia. The beginning of the noncancelable lease period for these leases ranged from 2014 to 2018 and the lease period ends between 2020 and 2028. These lease agreements contain between one and three options to renew the lease for a period of between two and five years. As of December 31, 2019, the exercise of the renewal options for these leases are not reasonably certain and, as a result, the payments associated with these renewals are not included in the measurement of the lease liability and ROU asset.

We also have options to extend the lease term of certain compression equipment used at the Summit Utica gathering system. The beginning of the noncancelable lease period for these leases was 2017 and the lease period ends in 2020. Upon expiration of the noncancelable lease period, we have the option to renew the leases on a month-to-month basis; we therefore have not included any amounts attributable to renewals in the measurement.

Our leases do not contain residual value guarantees.

In accordance with the provisions in our Revolving Credit Facility, our aggregate finance lease obligations cannot exceed $50 million in any period of twelve consecutive calendar months during the life of such leases.

In November 2019, we entered into a sublease agreement with a third party to sublease corporate office space in Houston, Texas. The noncancelable sublease period begins in 2020 and the sublease period ends in 2025. The sublease agreement contains one option to renew the lease for five years. We moved our corporate headquarters to the Houston office on March 2, 2020. Our future minimum sublease payments are approximately $1.2 million.

In March 2019, we entered into an agreement with a third party vendor to construct a transmission line to deliver electric power to the new 60 MMcf/d processing plant in the DJ Basin. The project is expected to cost approximately $7.8 million and we made an up-front payment of $3.0 million, which is included in the Property, plant and equipment, net caption on the consolidated balance sheet. During the second quarter of 2019, we exercised an option to increase the capacity of the transmission line for an additional cost of $4.3 million and we issued an irrevocable standby letter of credit payable to the vendor with an initial term of one year totaling $9.1 million, which reflects the expected remaining cost of the project. The letter of credit will automatically renew for successive twelve month periods following the initial term, subject to certain adjustments. Once construction is complete, the letter of credit will be adjusted to reflect the final construction cost. We determined the contract contained a lease based on the right to use the constructed transmission line to power the processing plant in the DJ Basin. The project is expected to be completed and the commencement date of the ROU asset will be on or before January 2021.

Our significant assumptions or judgments include the determination of whether a contract contains a lease and the discount rate used in our lease liabilities.

The rate implicit in our lease contracts is not readily determinable. In determining the discount rate used in our lease liabilities, we analyzed certain factors in our incremental borrowing rate, including collateral assumptions and the term used. Our incremental borrowing rate on the Revolving Credit Facility was 4.55% at December 31, 2019, which reflects the fixed rate at which we could borrow a similar amount, for a similar term and with similar collateral as in the lease contracts at the commencement date.

We adopted the following practical expedients in Topic 842 for all asset classes, which included (i) not being required to reassess whether any expired or existing contracts are or contain leases; (ii) not being required to reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with Topic 840 will be classified as operating leases, and all existing leases that were classified as capital leases in accordance with Topic 840 will be classified as finance leases); (iii) not being required to reassess initial direct costs for any existing leases; (iv) not recognizing ROU assets and lease liabilities that arise from short-term leases of twelve months or less for any class of underlying asset; (v) not allocating consideration in a contract between lease and nonlease (e.g., maintenance services) components for our leased office space and equipment; and (vi) not evaluating existing or expired land easements that were not previously accounted for as leases under Topic 840.

ROU assets (included in the Property, plant and equipment, net caption on our consolidated balance sheet) and lease liabilities (included in the Other current liabilities and Other noncurrent liabilities captions on our consolidated balance sheet) follow:

	December 31,
	2019
	(In thousands)

ROU assets
Operating	$	3,580
Finance		3,159
	$	6,739
Lease liabilities, current
Operating	$	1,221
Finance		1,246
	$	2,467
Lease liabilities, noncurrent
Operating	$	2,513
Finance		676
	$	3,189

Lease cost and Other information follow:

	Year ended December 31, 2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	1,559
Interest on lease liabilities (included in interest expense)		102
Operating lease cost (included in general and administrative expense)		3,159
	$	4,820

	Twelve months ended
	December 31, 2019
	(In thousands)
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	3,396
Operating cash outflows from finance leases		102
Financing cash outflows from finance leases		1,873
ROU assets obtained in exchange for new operating lease liabilities		1,218
ROU assets obtained in exchange for new finance lease liabilities		1,350
Weighted-average remaining lease term (years) - operating leases		5.8
Weighted-average remaining lease term (years) - finance leases		2.0
Weighted-average discount rate - operating leases		5	%
Weighted-average discount rate - finance leases		4	%

We recognize total lease expense incurred or allocated to us in general and administrative expenses. Lease expense related to operating leases, including lease expense incurred on our behalf and allocated to us, was as follows:

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Lease expense	$	3,851	$	3,928	$	3,772

Future minimum lease payments due under noncancelable leases at December 31, 2019, were as follows

	December 31, 2019
	(In thousands)
	Operating		Finance
2020	$	1,705	$	1,299
2021		1,004		616
2022		551		76
2023		408		—
2024		240		—
2025		153		—
Thereafter		742		—
Total future minimum lease payments	$	4,803	$	1,991

Future minimum lease payments due under noncancelable operating leases (under ASC 840) at December 31, 2018, were as follows:

	December 31,
	2018
	(In thousands)
2019	$	3,133
2020		1,018
2021		550
2022		506
2023		373
Thereafter		621
Total future minimum lease payments	$	6,201

Future payments due under finance leases (under ASC 840) at December 31, 2018, were as follows:

	December 31,
	2018
	(In thousands)
2019	$	1,473
2020		902
2021		174
Total finance lease obligations		2,549
Less: Amounts representing interest		(104	)
Net present value of finance lease obligations		2,445
Less: Amount representing current portion (included in Other current liabilities)		(1,406	)
Finance lease obligations, less current portion (included in Other noncurrent liabilities)	$	1,039

Environmental Matters. Although we believe that we are in material compliance with applicable environmental regulations, the risk of environmental remediation costs and liabilities are inherent in pipeline ownership and operation. Furthermore, we can provide no assurances that significant environmental remediation costs and liabilities will not be incurred by the Partnership in the future. We are currently not aware of any material contingent liabilities that exist with respect to environmental matters, except as noted below.

In 2015, Summit Investments learned of the rupture of a four-inch produced water gathering pipeline on the Meadowlark Midstream system near Williston, North Dakota. The incident, which was covered by Summit Investments' insurance policies, was subject to maximum coverage of $25.0 million from its pollution liability insurance policy and $200.0 million from its property and business interruption insurance policy. Summit Investments exhausted the $25.0 million pollution liability policy in 2015. We submitted property and business interruption claim requests to the insurers and reached a settlement in January 2017. In connection therewith, we recognized $2.6 million of business interruption recoveries and $0.4 million of property recoveries.

A rollforward of the aggregate accrued environmental remediation liabilities follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2018	$	5,344
Payments made		(3,808	)
Additional accruals		4,100
Accrued environmental remediation, December 31, 2018	$	5,636
Payments made		(2,284	)
Additional accruals		1,299
Accrued environmental remediation, December 31, 2019	$	4,651

As of December 31, 2019, we have recognized (i) a current liability for remediation effort expenditures expected to be incurred within the next 12 months and (ii) a noncurrent liability for estimated remediation expenditures and fines expected to be incurred subsequent to December 31, 2020. Each of these amounts represent our best estimate for costs expected to be incurred. Neither of these amounts has been discounted to its present value.

While we cannot predict the ultimate outcome of this matter with certainty for Summit Investments or Meadowlark Midstream, especially as it relates to any material liability as a result of any governmental proceeding related to the incident, we believe at this time that it is unlikely that SMLP or its General Partner will be subject to any material liability as a result of any governmental proceeding related to the rupture.

Legal Proceedings. The Partnership is involved in various litigation and administrative proceedings arising in the normal course of business. In the opinion of management, any liabilities that may result from these claims or those arising in the normal course of business would not individually or in the aggregate have a material adverse effect on the Partnership's financial position or results of operations.

REVENUE - Narrative1 (Details)	Dec. 31, 2019
Maximum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	25 years

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 2,573,451				$ 3,020,562				$ 2,573,451	$ 3,020,562	$ 2,894,793
Revenues	112,247	$ 100,187	$ 99,686	$ 131,408	133,671	$ 127,479	$ 128,183	$ 117,320	443,528	506,653	488,741
Depreciation and amortization									111,426	106,767	114,872
Capital expenditures									182,291	200,586	124,215
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,490,945				2,980,700				2,490,945	2,980,700	2,872,636
Revenues									415,906	428,492	469,224
Depreciation and amortization									108,822	105,024	113,754
Capital expenditures									163,028	189,951	121,174
Reportable Segments \| Utica Shale
Segment Reporting Information [Line Items]
Assets	206,368				207,357				206,368	207,357	212,311
Revenues									33,991	35,233	38,907
Depreciation and amortization									7,659	7,672	7,009
Capital expenditures									3,902	5,719	22,921
Reportable Segments \| Ohio Gathering
Segment Reporting Information [Line Items]
Assets	275,000				649,250				275,000	649,250	690,485
Reportable Segments \| Williston Basin
Segment Reporting Information [Line Items]
Assets	452,152				526,819				452,152	526,819	512,860
Revenues									105,651	123,650	161,503
Depreciation and amortization									19,829	22,642	33,772
Capital expenditures									30,861	25,202	17,309
Reportable Segments \| Barnett Shale
Segment Reporting Information [Line Items]
Assets	350,638				376,564				350,638	376,564	383,306
Revenues									71,802	68,265	71,667
Depreciation and amortization									16,575	15,325	15,001
Capital expenditures									184	1,370	569
Reportable Segments \| Marcellus Shale
Segment Reporting Information [Line Items]
Assets	184,631				208,790				184,631	208,790	217,362
Revenues									24,471	29,573	30,394
Depreciation and amortization									9,141	9,090	9,047
Capital expenditures									693	1,030	641
Reportable Segments \| DJ Basin
Segment Reporting Information [Line Items]
Assets	205,308				166,580				205,308	166,580	79,438
Revenues									26,050	15,294	11,860
Depreciation and amortization									3,732	3,133	2,636
Capital expenditures									80,487	64,920	7,150
Reportable Segments \| Permian Basin
Segment Reporting Information [Line Items]
Assets	185,708				145,702				185,708	145,702	57,590
Revenues									20,303	958
Depreciation and amortization									4,868	243	0
Capital expenditures									44,955	83,823	56,020
Reportable Segments \| Piceance Basin
Segment Reporting Information [Line Items]
Assets	631,140				699,638				631,140	699,638	719,284
Revenues									133,638	155,519	154,893
Depreciation and amortization									47,018	46,919	46,289
Capital expenditures									1,946	7,887	16,564
Corporate and Other
Segment Reporting Information [Line Items]
Assets	82,506				44,181				82,506	44,181	22,406
Revenues									30,552	88,286	26,446
Depreciation and amortization									2,604	1,743	1,118
Capital expenditures									19,263	10,635	3,041
Eliminations
Segment Reporting Information [Line Items]
Assets	$ 0				$ (4,319)				0	(4,319)	(249)
Revenues									$ (2,930)	$ (10,125)	$ (6,929)

UNIT-BASED AND NONCASH COMPENSATION - SMP Net Profits Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SMLP LTIP unit-based compensation	$ 8,171	$ 8,088	$ 7,878
SMLP LTIP \| General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SMLP LTIP unit-based compensation	$ 8,171	$ 8,328	$ 7,951

SEGMENT INFORMATION - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Equity Method Investments	$ 309,728	$ 649,250
Capital expenditures	182,291	200,586	$ 124,215
Corporate
Segment Reporting Information [Line Items]
Capital expenditures	1,600	3,300
Corporate and Other
Segment Reporting Information [Line Items]
Capital expenditures	19,263	10,635	3,041
Corporate and Other \| Double E
Segment Reporting Information [Line Items]
Capital Expenditures		9,600
Equity Method Investments	34,700
Reportable Segments
Segment Reporting Information [Line Items]
Capital expenditures	163,028	189,951	121,174
Reportable Segments \| Barnett Shale
Segment Reporting Information [Line Items]
Sales tax reimbursement	1,100
Capital expenditures	$ 184	$ 1,370	$ 569

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - shares			12 Months Ended
	Mar. 22, 2019	Feb. 26, 2019	Dec. 31, 2019	Dec. 31, 2018
Organization And Business Operations [Line Items]
Common limited partner capital (shares)			93,493,473	73,390,853
General Partner \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner interest	2.00%		2.00%
Common units \| General Partner
Organization And Business Operations [Line Items]
General partner units converted		8,750,000
SMP Holdings \| Common units
Organization And Business Operations [Line Items]
Common limited partner capital (shares)			45,318,866
SMP Holdings \| Common units \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner units converted	8,750,000
Summit Investments \| General Partner \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner interest	2.00%		2.00%
Energy Capital Partners \| Common units
Organization And Business Operations [Line Items]
Common limited partner capital (shares)			5,915,827

PROPERTY, PLANT, AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge					$ 60,507	$ 7,186	$ 188,702
Red Rock Gathering Company LLC
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge					14,200
Cash purchase price of disposals					12,000
Permian Basin
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge					726	761
Asset impairment charges			$ 700
DJ Basin
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge					34,913	9
Asset impairment charges				$ 34,700
Barnett Shale
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge					9,629
Asset impairment charges				$ 9,700
Williston Basin
Property, Plant and Equipment [Line Items]
Long-lived assets impairment charge	$ 3,900	$ 101,900			$ 10	$ 3,972	$ 101,961

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($)
$ in Thousands

11 Months Ended

12 Months Ended

Nov. 30, 2019

Nov. 30, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Equity Method Investment [Roll Forward]

Investment in Ohio Gathering, December 31

$ 649,250

December cash distributions

37,300

$ 35,271

$ 40,220

Impairment loss

337,851

10,888

2,223

Investment in equity method investees, net of basis difference, November 30

309,728

649,250

OGC | Summit Midstream Partners, LLC

Equity Method Investment [Roll Forward]

Investment in Ohio Gathering, December 31

275,000

$ 649,250

275,000

649,250

December cash distributions

2,700

2,736

Impairment loss

232,521

^[1]

5,652

^[1]

$ 329,700

7,700

Loss contingency

2,040

Basis difference

(116,832)

Investment in equity method investees, net of basis difference, November 30

$ 510,221

$ 542,846

$ 275,000

$ 649,250

[1]

(1)

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 3,133
2020	1,018
2021	550
2022	506
2023	373
Thereafter	621
Total future minimum lease payments	$ 6,201

FINANCIAL INSTRUMENTS

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

FINANCIAL INSTRUMENTS

11. FINANCIAL INSTRUMENTS

Concentrations of Credit Risk. Financial instruments that potentially subject us to concentrations of credit risk consist of cash and cash equivalents, restricted cash and accounts receivable. We maintain our cash and cash equivalents and restricted cash in bank deposit accounts that frequently exceed federally insured limits. We have not experienced any losses in such accounts and do not believe we are exposed to any significant risk.

Accounts receivable primarily comprise amounts due for the gathering, compression, treating and processing services we provide to our customers and also the sale of natural gas liquids resulting from our processing services. This industry concentration has the potential to impact our overall exposure to credit risk, either positively or negatively, in that our customers may be similarly affected by changes in economic, industry or other conditions. We monitor the creditworthiness of our counterparties and can require letters of credit or other forms of credit assurance for receivables from counterparties that are judged to have substandard credit, unless the credit risk can otherwise be mitigated. Our top five customers or counterparties accounted for 46% of total accounts receivable at December 31, 2019, compared to 39% as of December 31, 2018.

Fair Value. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable and trade accounts payable reported on the consolidated balance sheet approximates fair value due to their short-term maturities.

The Deferred Purchase Price Obligation's carrying value is its fair value because carrying value represents the present value of the payment which can be made at any time prior to January 15, 2022. In November 2019, we and SMP Holdings entered into a second amendment (the “Second Amendment”) to the Contribution Agreement between us and SMP Holdings dated February 25, 2016, as amended. On November 15, 2019, we made a cash payment of $51.75 million and issued 10,714,285 common units to SMP Holdings (the “November 2019 Prepayment”). In addition, the parties reduced the Remaining Consideration due to SMP Holdings by $19.25 million. Following the November 2019 Prepayment, the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020. The form(s) of Remaining Consideration to be delivered by us to SMP Holdings continue to be determinable by us in our sole discretion (see Note 17 for additional information).

A summary of the estimated fair value of our debt financial instruments follows.

	December 31, 2019				December 31, 2018
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Summit Holdings 5.5% Senior Notes ($300.0 million principal)	$	298,314	$	266,750	$	297,638	$	286,625
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		494,985		382,708		494,093		455,208

The carrying value on the balance sheet of the Revolving Credit Facility is its fair value due to its floating interest rate. The fair value for the Senior Notes is based on an average of nonbinding broker quotes as of December 31, 2019 and 2018. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the Senior Notes.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

FINANCIAL INSTRUMENTS - Concentration Risk - Narrative (Details) - Customer	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
CONCENTRATIONS OF RISK
Number of top customers	5
Five Largest Customers \| Accounts receivable \| Customer Concentration Risk
CONCENTRATIONS OF RISK
Concentration risk, percentage	46.00%	39.00%

UNAUDITED QUARTERLY FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Limited Partners' Capital Account [Line Items]
Revenues	$ 112,247	$ 100,187	$ 99,686	$ 131,408	$ 133,671	$ 127,479	$ 128,183	$ 117,320	$ 443,528	$ 506,653	$ 488,741
Net (loss) income attributable to SMLP	(327,083)	(10,645)	4,809	(36,914)	38,654	57,430	(49,971)	(3,930)	(369,833)	42,183	85,687
Less net income and IDRs attributable to General Partner				12	2,907	3,279	1,140	2,058
Net (loss) income attributable to limited partners									(369,845)	32,799	75,485
Series A Preferred Units
Limited Partners' Capital Account [Line Items]
Net (loss) income attributable to limited partners	7,125	7,125	7,125	7,125	7,125	7,125	7,125	7,125	28,500	28,500	3,563
Series A Preferred Units \| Subsidiary
Limited Partners' Capital Account [Line Items]
Net (loss) income attributable to limited partners	58								58	0	0
Common units
Limited Partners' Capital Account [Line Items]
Net (loss) income attributable to limited partners	$ (334,266)	$ (17,770)	$ (2,316)	$ (44,051)	$ 28,622	$ 47,026	$ (58,236)	$ (13,113)	$ (398,403)	$ 4,299	$ 71,922
Common unit – basic	$ (3.79)	$ (0.21)	$ (0.03)	$ (0.58)	$ 0.39	$ 0.64	$ (0.79)	$ (0.18)	$ (4.84)	$ 0.06	$ 0.99
Common unit – diluted	$ (3.79)	$ (0.21)	$ (0.03)	$ (0.58)	$ 0.39	$ 0.64	$ (0.79)	$ (0.18)	$ (4.84)	$ 0.06	$ 0.98

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING - Tioga Midstream Disposition (Details) - Tioga Midstream, LLC - Disposal, not discontinued operations - Purchase and Sale Agreement $ in Millions		1 Months Ended
	Mar. 22, 2019 USD ($)	Feb. 28, 2019 USD ($) Agreement
Business Acquisition [Line Items]
Number of purchase and sale agreements \| Agreement		2
Cash purchase price of disposals		$ 90.0
Gain on sale of business	$ 0.9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Gathering and processing systems and related equipment \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	12 years
Gathering and processing systems and related equipment \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	30 years
Other \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	4 years
Other \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	15 years

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Mezzanine Capital and Schedule of Units (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Series A Preferred Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	300,000	300,000	0
Units issued in connection with offering			300,000
General partner units converted	0
Net units issued under SMLP LTIP (in shares)	0	0	0
Units issued under ATM program (in shares)			0
General Partner 2% capital contribution (in shares)			0
Units, ending balance (in shares)	300,000	300,000	300,000
DPPO partial settlement	0
Common
Rollforwards of the number of partner units
Units, beginning balance (in shares)	73,390,853	73,085,996	72,111,121
Units issued in connection with offering			0
General partner units converted	8,750,000
Net units issued under SMLP LTIP (in shares)	638,335	304,857	211,327
Units issued under ATM program (in shares)			763,548
General Partner 2% capital contribution (in shares)			0
Units, ending balance (in shares)	93,493,473	73,390,853	73,085,996
DPPO partial settlement	10,714,285
General Partner Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	1,490,999	1,490,999	1,471,187
Units issued in connection with offering			0
General partner units converted	(1,490,999)
Net units issued under SMLP LTIP (in shares)	0	0	0
Units issued under ATM program (in shares)			0
General Partner 2% capital contribution (in shares)			19,812
Units, ending balance (in shares)	0	1,490,999	1,490,999
DPPO partial settlement	0

UNIT-BASED AND NONCASH COMPENSATION - Schedule of Intrinsic Values (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SMLP LTIP \| Phantom Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of vested LTIP awards	$ 5,940	$ 5,393	$ 6,657

AMORTIZING INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

AMORTIZING INTANGIBLE ASSETS

6. AMORTIZING INTANGIBLE ASSETS

Details regarding our intangible assets, all of which are subject to amortization, follow.

	December 31, 2019
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(15,125	)	$	9,070
Contract intangibles		278,448		(169,549	)		108,899
Rights-of-way		157,175		(42,866	)		114,309
Total intangible assets	$	459,818	$	(227,540	)	$	232,278

	December 31, 2018
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(13,905	)	$	10,290
Contract intangibles		278,448		(143,962	)		134,486
Rights-of-way		166,209		(37,569	)		128,640
Total intangible assets	$	468,852	$	(195,436	)	$	273,416

In December 2019, in connection with the cancellation of a project, we determined certain rights-of-way intangible assets in the Permian Basin would no longer be utilized (see Note 5). As a result, we recorded an impairment charge of $0.6 million in the fourth quarter of 2019.

Also in early 2019, certain events occurred which indicated that certain long-lived assets relating to the Barnett Shale reporting segment could be impaired (see Note 5). In connection with this evaluation, we evaluated the related intangible assets associated therewith for impairment consisting of rights-of-way intangible assets. We concluded the rights-of-way intangible assets were also impaired and, as a result, we recorded an impairment charge of $0.5 million in the first quarter of 2019.

In December 2017, in connection with certain strategic initiatives, we evaluated certain long-lived assets relating to the Bison Midstream system within the Williston Basin reporting segment (see Note 5). In connection with this evaluation, we evaluated the related intangible assets associated therewith for impairment consisting of contract intangible assets and rights-of-way intangible assets. We concluded the contract intangible assets were also impaired and, as a result, we recorded an impairment charge of $85.2 million.

We recognized amortization expense in Other revenues as follows:

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(1,220	)	$	(1,555	)	$	(1,555	)

We recognized amortization expense in costs and expenses as follows:

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Amortization expense – contract intangibles	$	25,587	$	26,141	$	34,202
Amortization expense – rights-of-way		6,278		6,448		6,153

The estimated aggregate annual amortization expected to be recognized for as of December 31, 2019 for each of the five succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2020	$	31,901
2021		28,209
2022		25,142
2023		25,088
2024		14,917

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Narrative (Details)						1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 29, 2020 USD ($) $ / shares	Jan. 21, 2020	Jan. 16, 2020 USD ($) $ / shares shares	Mar. 22, 2019 USD ($) shares	Feb. 26, 2019 shares	Dec. 31, 2019 USD ($) $ / shares shares	Nov. 30, 2018 USD ($)	Nov. 30, 2017 USD ($) $ / shares shares	Feb. 28, 2017 USD ($) shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2019 USD ($) Transaction $ / shares shares	Dec. 31, 2018 USD ($) Transaction $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Partners Capital [Line Items]
Fair value											$ 0
Aggregate gross proceeds											$ 0	$ 0	$ 17,078,000
Preferred units issued \| shares						300,000				300,000	300,000	300,000
Repayment of outstanding revolving credit facility											$ 158,000,000	$ 84,000,000	$ 634,500,000
Maximum period following end of quarter to distribute all available cash											45 days
Per-unit annual distributions to unitholders (in dollars per unit) \| $ / shares											$ 1.4375	$ 2.300	$ 2.300
Subsequent Event
Partners Capital [Line Items]
Per-unit annual distributions to unitholders (in dollars per unit) \| $ / shares	$ 0.125
Cash paid to unit holders	$ 11,700,000
Cash distribution date	Feb. 14, 2020
Cash distribution date of record	Feb. 07, 2020
Revolving credit facility
Partners Capital [Line Items]
Repayment of outstanding revolving credit facility								$ 293,200,000
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued \| shares								300,000
Interest in partnership per unit \| $ / shares								$ 1,000
Distribution rate								9.50%			7.00%
Liquidation preference per unit \| $ / shares						$ 1,000		$ 1,000		$ 1,000	$ 1,000
Distribution percentage of liquidation preference rate description											three-month LIBOR plus a spread of 7.43%
Proceeds from underwritten issuance of common units, net of costs											$ 27,400,000
Series A Preferred Units \| Paid-in-kind
Partners Capital [Line Items]
Pro-rated issuance of preferred units \| shares										47
Pro-rated distribution of preferred units \| $ / shares										$ 1.5556
Pro-rated distribution of preferred units											$ 70,000
Series A Preferred Units \| Subsequent Event \| Paid-in-kind
Partners Capital [Line Items]
Distribution percentage of subsidiary unit		7.00%
Distribution percentage of liquidation preference rate of undrawn commitment units		1.00%
Series A Preferred Units \| Permian Holdco
Partners Capital [Line Items]
Preferred units issued \| shares						30,000				30,000	30,000
Series A preferred per unit, price \| $ / shares						$ 1,000				$ 1,000	$ 1,000
Series A Preferred Units \| Permian Holdco \| Subsequent Event
Partners Capital [Line Items]
Preferred units issued \| shares			10,000
Series A preferred per unit, price \| $ / shares			$ 1,000
Series A Preferred Units \| Permian Holdco \| Double E
Partners Capital [Line Items]
Proceeds from underwritten issuance of common units, net of costs						$ 27,400,000
Series A Preferred Units \| Permian Holdco \| Double E \| Subsequent Event
Partners Capital [Line Items]
Proceeds from underwritten issuance of common units, net of costs			$ 9,700,000
Series A Preferred Units \| LIBOR
Partners Capital [Line Items]
Distribution percentage of liquidation preference rate								7.43%
Subsidiary of Summit Investments
Partners Capital [Line Items]
Purchase of noncontrolling interest							$ 10,900,000
Summit Midstream Partners, LP \| Common units \| SMP Holdings
Partners Capital [Line Items]
General partner units converted \| shares				8,750,000
Summit Midstream OpCo, LP \| Subsidiary of Summit Investments
Partners Capital [Line Items]
Ownership interest							1.00%
General Partner
Partners Capital [Line Items]
Fair value											$ (22,222,000)
General Partner \| Common units
Partners Capital [Line Items]
General partner units converted \| shares					8,750,000
General Partner \| Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner interest				2.00%							2.00%
Limited Partner \| Public Offering \| 2016 SRS
Partners Capital [Line Items]
Units issued under ATM program (in shares) \| shares									4,000,000
Proceeds from Issuance of common stock									$ 0
Common
Partners Capital [Line Items]
General partner units converted \| shares											8,750,000
Fair value											$ 22,222,000
Units issued under ATM program (in shares) \| shares													763,548
Units issued in connection with offering \| shares													0
Common \| Public Offering
Partners Capital [Line Items]
Aggregate offering price									$ 150,000,000.0
Transactions under ATM Program \| Transaction											0	0
Units issued in connection with offering \| shares													763,548
Aggregate gross proceeds													$ 17,700,000
Compensation paid to sales agents													$ 200,000
GP/IDR Exchange \| Summit Midstream Partners, LP \| Common units \| SMP Holdings
Partners Capital [Line Items]
General partner units converted \| shares				8,750,000
Fair value				$ 84,500,000
GP/IDR Exchange \| General Partner \| Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner interest				2.00%
GP/IDR Exchange \| General Partner \| Summit Midstream Partners, LP \| SMP Holdings
Partners Capital [Line Items]
General partner interest				2.00%
GP/IDR Exchange \| Limited Partner \| Summit Midstream Partners, LP \| SMP Holdings
Partners Capital [Line Items]
Limited partner interest ownership percentage											41.80%
GP/IDR Exchange \| Limited Partner \| Summit Midstream Partners, LP \| Affiliate of Energy Capital Partners II, LLC
Partners Capital [Line Items]
Limited partner interest ownership percentage											7.20%

DEBT - Revolving Credit Facility (Narrative) (Details)	1 Months Ended	12 Months Ended
DEBT - Revolving Credit Facility (Narrative) (Details)	May 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	May 26, 2017	May 25, 2017
Line of Credit Facility [Line Items]
Line of credit facility, outstanding amount			$ 9,100,000
Revolving credit facility
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,250,000,000	$ 100,000,000
Revolving credit facility maturity date	2022-05
Accordion feature	$ 250,000,000.0
Leverage ratio				5.50	5.00
Senior secured leverage ratio	3.75
Commitment fee on unused portion of the facility		0.50%
Interest rate at period end		4.55%
Unused portion under the facility		$ 563,900,000
Line of credit facility, outstanding amount		9,100,000
Cumulative payment obligations, maximum		50,000,000.0
Debt issuance costs		6,200,000
Debt defaults		$ 0
Revolving credit facility \| LIBOR
Line of Credit Facility [Line Items]
Applicable margin		2.75%
Revolving credit facility \| Minimum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility		0.30%
Ratio of consolidated trailing 12-month EBITDA to net interest expense		2.5
Revolving credit facility \| Minimum \| ABR
Line of Credit Facility [Line Items]
Applicable margin		0.75%
Revolving credit facility \| Minimum \| LIBOR
Line of Credit Facility [Line Items]
Applicable margin		1.75%
Revolving credit facility \| Maximum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility		0.50%
Ratio of total net indebtedness to consolidated trailing 12-month EBITDA		5.50
Ratio of first lien net indebtedness to consolidated trailing 12-month EBITDA		3.75
Revolving credit facility \| Maximum \| ABR
Line of Credit Facility [Line Items]
Applicable margin		1.75%
Revolving credit facility \| Maximum \| LIBOR
Line of Credit Facility [Line Items]
Applicable margin		2.75%

UNIT-BASED AND NONCASH COMPENSATION

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

UNIT-BASED AND NONCASH COMPENSATION

14. UNIT-BASED AND NONCASH COMPENSATION

SMLP Long-Term Incentive Plan. The SMLP LTIP provides for equity awards to eligible officers, employees, consultants and directors of our General Partner and its affiliates, thereby linking the recipients' compensation directly to SMLP’s performance. The SMLP LTIP is administered by our General Partner's Board of Directors, though such administration function may be delegated to a committee appointed by the board. A total of 5.0 million common units was reserved for issuance pursuant to and in accordance with the SMLP LTIP. As of December 31, 2019, approximately 1.3 million common units remained available for future issuance.

The SMLP LTIP provides for the granting, from time to time, of unit-based awards, including common units, restricted units, phantom units, unit options, unit appreciation rights, distribution equivalent rights, profits interest units and other unit-based awards. Grants are made at the discretion of the Board of Directors or Compensation Committee of our General Partner. The administrator of the SMLP LTIP may make grants under the SMLP LTIP that contain such terms, consistent with the SMLP LTIP, as the administrator may determine are appropriate, including vesting conditions. The administrator of the SMLP LTIP may, in its discretion, base vesting on the grantee's completion of a period of service or upon the achievement of specified financial objectives or other criteria or upon a change of control (as defined in the SMLP LTIP) or as otherwise described in an award agreement. Termination of employment prior to vesting will result in forfeiture of the awards, except in limited circumstances as described in the plan documents. Units that are canceled or forfeited will be available for delivery pursuant to other awards.

The following table presents phantom unit activity:

	Units			Weighted-average grant date fair value
Nonvested phantom units, January 1, 2017		691,955		$	19.59
Phantom units granted		371,972			22.50
Phantom units vested		(293,222	)		24.76
Phantom units forfeited		(21,431	)		20.07
Nonvested phantom units, December 31, 2017		749,274			20.07
Phantom units granted		515,358			15.25
Phantom units vested		(359,016	)		22.39
Phantom units forfeited		(41,492	)		17.27
Nonvested phantom units, December 31, 2018		864,124			17.11
Phantom units granted		1,913,099			6.48
Phantom units vested		(602,617	)		16.78
Phantom units forfeited		(68,611	)		12.87
Nonvested phantom units, December 31, 2019		2,105,995		$	7.69

A phantom unit is a notional unit that entitles the grantee to receive a common unit upon the vesting of the phantom unit or on a deferred basis upon specified future dates or events or, in the discretion of the administrator, cash equal to the fair market value of a common unit. Distribution equivalent rights for each phantom unit provide for a lump sum cash amount equal to the accrued distributions from the grant date to be paid in cash upon the vesting date.

Phantom units granted to date generally vest ratably over a three-year period. Grant date fair value is determined based on the closing price of our common units on the date of grant multiplied by the number of phantom units awarded to the grantee. Forfeitures are recorded as incurred. Holders of all phantom units granted to date are entitled to receive distribution equivalent rights for each phantom unit, providing for a lump sum cash amount equal to the accrued distributions from the grant date of the phantom units to be paid in cash upon the vesting date. Upon vesting, phantom unit awards may be settled, at our discretion, in cash and/or common units, but the current intention is to settle all phantom unit awards with common units.

The intrinsic value of phantom units that vested during the years ended December 31, follows.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Intrinsic value of vested LTIP awards	$	5,940	$	5,393	$	6,657

As of December 31, 2019, the unrecognized unit-based compensation related to the SMLP LTIP was $8.5 million. Incremental unit-based compensation will be recorded over the remaining weighted-average vesting period of approximately 1.6 years.

Unit-based compensation recognized in general and administrative expense related to awards under the SMLP LTIP follows.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
SMLP LTIP unit-based compensation	$	8,171	$	8,328	$	7,951

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income attributable to limited partners									$ (369,845)	$ 32,799	$ 75,485
Phantom Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU									175	2	42
Limited Partner Interest Before Subordinated Units Converted To Common Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income attributable to limited partners									$ (369,845)	$ 32,799	$ 75,485
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income attributable to limited partners	$ (334,266)	$ (17,770)	$ (2,316)	$ (44,051)	$ 28,622	$ 47,026	$ (58,236)	$ (13,113)	$ (398,403)	$ 4,299	$ 71,922
Weighted-average common units outstanding – basic									82,365	73,304	72,705
Effect of nonvested phantom units									0	311	342
Weighted-average common units outstanding – diluted									82,365	73,615	73,047
Common unit – basic	$ (3.79)	$ (0.21)	$ (0.03)	$ (0.58)	$ 0.39	$ 0.64	$ (0.79)	$ (0.18)	$ (4.84)	$ 0.06	$ 0.99
Common unit – diluted	$ (3.79)	$ (0.21)	$ (0.03)	$ (0.58)	$ 0.39	$ 0.64	$ (0.79)	$ (0.18)	$ (4.84)	$ 0.06	$ 0.98
Series A Preferred Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income attributable to limited partners	$ 7,125	$ 7,125	$ 7,125	$ 7,125	$ 7,125	$ 7,125	$ 7,125	$ 7,125	$ 28,500	$ 28,500	$ 3,563
Series A Preferred Units \| Subsidiary
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income attributable to limited partners	$ 58								$ 58	$ 0	$ 0

GOODWILL

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

GOODWILL

7. GOODWILL

Goodwill for the year ended December 31, 2018 of $16.2 million was related to the acquisition of the Mountaineer Midstream system in 2013.

Accumulated goodwill impairments by reportable segment for those reporting units that have previously recognized goodwill follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Accumulated goodwill impairment:
Piceance Basin	$	45,478	$	45,478	$	45,478
Williston Basin		257,572		257,572		257,572
Marcellus Shale		16,211		—		—
Total accumulated goodwill impairment	$	319,261	$	303,050	$	303,050

We evaluate goodwill whenever events or circumstances indicate that it is more likely than not that the fair value of a reporting unit is less than its carrying value, including goodwill. If the reporting unit’s fair value exceeds its carrying value, including goodwill, we conclude that the goodwill of the reporting unit has not been impaired and no further work is performed. If we determine that the reporting unit’s carrying value, including goodwill, exceeds its fair value, we recognize the excess of the carrying value over the fair value as a goodwill impairment loss.

We performed our annual goodwill impairment testing for the Mountaineer Midstream reporting unit as of September 30, 2019 using a combination of the income and market approaches. We determined that the fair value of the Mountaineer Midstream reporting unit did not exceed its carrying value, including goodwill. As a result, we recognized a goodwill impairment charge of $16.2 million for the year ended December 31, 2019.

We had no impairments of goodwill for the years ended December 31, 2018 and 2017.

Fair Value Measurement. Our impairment determinations, in the context of (i) our annual impairment evaluations and (ii) our other-than-annual impairment evaluations involved significant assumptions and judgments. Differing assumptions regarding any of these inputs could have a significant effect on the valuations. As such, the fair value measurements utilized within these models are classified as non-recurring Level 3 measurements in the fair value hierarchy because they are not observable from objective sources.

DEFERRED REVENUE - Rollforward of deferred revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 11,467	$ 10,088
Current deferred revenue, Additions	25,326	26,407
Current deferred revenue, Less revenue recognized	23,300	25,028
Current deferred revenue, ending balance	13,493	11,467
Noncurrent deferred revenue, beginning balance	39,504	35,528
Noncurrent deferred revenue, Additions	15,093	16,502
Noncurrent deferred revenue, Less reclassification to current deferred revenue	15,888	12,526
Noncurrent deferred revenue, ending balance	38,709	39,504
Utica Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18	18
Current deferred revenue, Additions	18	18
Current deferred revenue, Less revenue recognized	18	18
Current deferred revenue, ending balance	18	18
Noncurrent deferred revenue, beginning balance	21	39
Noncurrent deferred revenue, Additions	0	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	18	18
Noncurrent deferred revenue, ending balance	3	21
Williston Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,414	1,017
Current deferred revenue, Additions	2,262	1,744
Current deferred revenue, Less revenue recognized	1,743	1,347
Current deferred revenue, ending balance	1,933	1,414
Noncurrent deferred revenue, beginning balance	4,393	4,215
Noncurrent deferred revenue, Additions	1,940	1,851
Noncurrent deferred revenue, Less reclassification to current deferred revenue	2,699	1,673
Noncurrent deferred revenue, ending balance	3,634	4,393
DJ Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	739	358
Current deferred revenue, Additions	5,165	943
Current deferred revenue, Less revenue recognized	3,044	562
Current deferred revenue, ending balance	2,860	739
Noncurrent deferred revenue, beginning balance	7,284	4,505
Noncurrent deferred revenue, Additions	5,470	3,720
Noncurrent deferred revenue, Less reclassification to current deferred revenue	5,165	941
Noncurrent deferred revenue, ending balance	7,589	7,284
Piceance Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	7,616	7,038
Current deferred revenue, Additions	16,211	21,955
Current deferred revenue, Less revenue recognized	16,813	21,377
Current deferred revenue, ending balance	7,014	7,616
Noncurrent deferred revenue, beginning balance	17,942	18,219
Noncurrent deferred revenue, Additions	6,104	7,869
Noncurrent deferred revenue, Less reclassification to current deferred revenue	6,336	8,146
Noncurrent deferred revenue, ending balance	17,710	17,942
Barnett Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,642	1,619
Current deferred revenue, Additions	1,632	1,651
Current deferred revenue, Less revenue recognized	1,644	1,628
Current deferred revenue, ending balance	1,630	1,642
Noncurrent deferred revenue, beginning balance	9,628	8,217
Noncurrent deferred revenue, Additions	1,579	3,062
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,632	1,651
Noncurrent deferred revenue, ending balance	9,575	9,628
Marcellus Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38	38
Current deferred revenue, Additions	38	96
Current deferred revenue, Less revenue recognized	38	96
Current deferred revenue, ending balance	38	38
Noncurrent deferred revenue, beginning balance	236	333
Noncurrent deferred revenue, Additions	0	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	38	97
Noncurrent deferred revenue, ending balance	$ 198	$ 236

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING - Restructuring Activities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Employee Related Costs
Business Acquisition [Line Items]
Restructuring and related cost, expected cost	$ 6.0
Severance costs	3.8
Employee related cost included in current liabilities	2.7
Consultants
Business Acquisition [Line Items]
Restructuring costs	1.2
Restructuring and related cost, expected cost	0.2
Consultant related liabilities current	0.6
General and administrative expense
Business Acquisition [Line Items]
Restructuring costs	$ 5.0

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Contract With Customer Asset And Liability [Abstract]
Contract assets, beginning of period	$ 8,755	$ 0
Additions	18,077	26,403
Transfers out	(22,930)	(17,648)
Contract assets, end of period	$ 3,902	$ 8,755

PARTNERS' CAPITAL AND MEZZANINE CAPITAL (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Schedule of partner units activity

A rollforward of the number of common limited partner, preferred limited partner and General Partner units follows.

	Limited partners
	Series A Preferred Units		Common		General Partner
Units, January 1, 2017		—		72,111,121		1,471,187
Units issued in connection with the November 2017 Equity Offering		300,000		—		—
Net units issued under the SMLP LTIP		—		211,327		—
Units issued under ATM program		—		763,548		—
General Partner 2% contribution		—		—		19,812
Units, December 31, 2017		300,000		73,085,996		1,490,999
Net units issued under the SMLP LTIP		—		304,857		—
Units, December 31, 2018		300,000		73,390,853		1,490,999
Conversion of General Partner economic interests		—		8,750,000		(1,490,999	)
Net units issued under the SMLP LTIP		—		638,335		—
DPPO partial settlement		—		10,714,285		—
Units, December 31, 2019		300,000		93,493,473		—

Details of cash distributions

Our payment of IDRs as reported in distributions to unitholders – General Partner in the statements of partners' capital during the years ended December 31 follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
IDR payments	$	2,139	$	8,535	$	8,460

We paid the following per-unit distributions during the years ended December 31:

	Year ended December 31,
	2019		2018		2017
Per-unit distributions to unitholders	$	1.4375	$	2.300	$	2.300

LEASES, COMMITMENTS AND CONTINGENCIES - Future Minimum Lease Payments Due and Future Minimum Rentals to be Received under Noncancelable Leases (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating lease, Future minimum lease payments, 2020	$ 1,705
Operating lease, Future minimum lease payments, 2021	1,004
Operating lease, Future minimum lease payments, 2022	551
Operating lease, Future minimum lease payments, 2023	408
Operating lease, Future minimum lease payments, 2024	240
Operating lease, Future minimum lease payments, 2025	153
Operating lease, Future minimum lease payments, Thereafter	742
Operating lease, Total future minimum lease payments	4,803
Finance lease, Future minimum lease payments, 2020	1,299
Finance lease, Future minimum lease payments, 2021	616
Finance lease, Future minimum lease payments, 2022	76
Finance lease, Total future minimum lease payments	$ 1,991

GOODWILL (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Rollforward of goodwill by reportable segment

Accumulated goodwill impairments by reportable segment for those reporting units that have previously recognized goodwill follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Accumulated goodwill impairment:
Piceance Basin	$	45,478	$	45,478	$	45,478
Williston Basin		257,572		257,572		257,572
Marcellus Shale		16,211		—		—
Total accumulated goodwill impairment	$	319,261	$	303,050	$	303,050

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Future Payments Due Under Finance Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 1,473
2020	902
2021	174
Total finance lease obligations	2,549
Less: Amounts representing interest	(104)
Net present value of finance lease obligations	2,445
Less: Amount representing current portion (included in Other current liabilities)	(1,406)
Finance lease obligations, less current portion (included in Other noncurrent liabilities)	$ 1,039

FINANCIAL INSTRUMENTS - Fair Value Narrative (Details) - Drop Down Assets 2016 Acquisition - USD ($) $ in Thousands				1 Months Ended	10 Months Ended	12 Months Ended
	Mar. 31, 2020	Nov. 15, 2019	Nov. 07, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Payments to Acquire Businesses, Gross		$ 51,750	$ 51,750
Business acquisition, reduced amount of consideration			19,250
Remaining cash consideration payable			$ 180,750		$ 303,500
Remaining consideration description			the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020	Remaining Consideration at $303.5 million, with such amount to be paid by the Partnership in one or more payments over the period from March 1, 2020 through December 31, 2020, in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, at the discretion of the Partnership. At least 50% of the Remaining Consideration must be paid on or before June 30, 2020 and interest will accrue at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020		the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest will accrue (and will be payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020
Scenario Forecast
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%				8.00%
Common units
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Business acquisition, share issued (shares)		10,714,285	10,714,285

LEASES, COMMITMENTS AND CONTINGENCIES - Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Lease expense	$ 3,851	$ 3,928	$ 3,772

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Right of Use Assets and Lease Liabilities (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Right-of-use asset	$ 3,580
Finance	3,159
Total	6,739
Lease liabilities, current
Operating	1,221
Finance	1,246
Total	2,467
Lease liabilities, noncurrent
Operating	2,513
Finance	676
Total	$ 3,189

UNIT-BASED AND NONCASH COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of activity

The following table presents phantom unit activity:

	Units			Weighted-average grant date fair value
Nonvested phantom units, January 1, 2017		691,955		$	19.59
Phantom units granted		371,972			22.50
Phantom units vested		(293,222	)		24.76
Phantom units forfeited		(21,431	)		20.07
Nonvested phantom units, December 31, 2017		749,274			20.07
Phantom units granted		515,358			15.25
Phantom units vested		(359,016	)		22.39
Phantom units forfeited		(41,492	)		17.27
Nonvested phantom units, December 31, 2018		864,124			17.11
Phantom units granted		1,913,099			6.48
Phantom units vested		(602,617	)		16.78
Phantom units forfeited		(68,611	)		12.87
Nonvested phantom units, December 31, 2019		2,105,995		$	7.69

Schedule of intrinsic values

The intrinsic value of phantom units that vested during the years ended December 31, follows.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Intrinsic value of vested LTIP awards	$	5,940	$	5,393	$	6,657

Schedule of unit-based compensation recognized in general and administrative expense

Unit-based compensation recognized in general and administrative expense related to awards under the SMLP LTIP follows.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
SMLP LTIP unit-based compensation	$	8,171	$	8,328	$	7,951

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Feb. 14, 2020	Jun. 28, 2019
Cover [Abstract]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 309,575,112
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	SMLP
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		93,613,194
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Units
Security Exchange Name	NYSE
Entity File Number	001-35666
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-5200503
Entity Address, Address Line One	910 Louisiana Street
Entity Address, Address Line Two	Suite 4200
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	832
Local Phone Number	413-4770
Document Annual Report	true
Document Transition Report	false

SEGMENT INFORMATION (Tables)

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

Schedule of assets by reportable segment

Assets by reportable segment follow.

	December 31,
	2019		2018			2017
	(In thousands)
Assets (1):
Utica Shale	$	206,368	$	207,357		$	212,311
Ohio Gathering		275,000		649,250			690,485
Williston Basin		452,152		526,819			512,860
DJ Basin		205,308		166,580			79,438
Permian Basin		185,708		145,702			57,590
Piceance Basin		631,140		699,638			719,284
Barnett Shale		350,638		376,564			383,306
Marcellus Shale		184,631		208,790			217,362
Total reportable segment assets		2,490,945		2,980,700			2,872,636
Corporate and Other		82,506		44,181			22,406
Eliminations		—		(4,319	)		(249	)
Total assets	$	2,573,451	$	3,020,562		$	2,894,793

(1) At December 31, 2019, Corporate and Other included $34.7 million relating to our investment in Double E (included in the Investment in equity method investees caption of the consolidated balance sheet). At December 31, 2018, Corporate and Other included $9.6 million of capital expenditures relating to the Double E Project.

Schedule of segment reporting information

Revenues by reportable segment follow.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Revenues (1):
Utica Shale	$	33,991		$	35,233		$	38,907
Williston Basin		105,651			123,650			161,503
DJ Basin		26,050			15,294			11,860
Permian Basin		20,303			958			—
Piceance Basin		133,638			155,519			154,893
Barnett Shale		71,802			68,265			71,667
Marcellus Shale		24,471			29,573			30,394
Total reportable segments revenue		415,906			428,492			469,224
Corporate and Other		30,552			88,286			26,446
Eliminations		(2,930	)		(10,125	)		(6,929	)
Total revenues	$	443,528		$	506,653		$	488,741

Depreciation and amortization, including the amortization expense associated with our favorable and unfavorable (for 2018) gas gathering contracts as reported in other revenues, by reportable segment follows.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	7,659	$	7,672	$	7,009
Williston Basin		19,829		22,642		33,772
DJ Basin		3,732		3,133		2,636
Permian Basin		4,868		243		—
Piceance Basin		47,018		46,919		46,289
Barnett Shale (2)		16,575		15,325		15,001
Marcellus Shale		9,141		9,090		9,047
Total reportable segment depreciation and amortization		108,822		105,024		113,754
Corporate and Other		2,604		1,743		1,118
Total depreciation and amortization	$	111,426	$	106,767	$	114,872

(1) Excludes depreciation and amortization recognized by Ohio Gathering due to equity method accounting.

(2) Includes the amortization expense associated with our favorable and unfavorable (for 2018) gas gathering contracts as reported in Other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	3,902	$	5,719	$	22,921
Williston Basin		30,861		25,202		17,309
DJ Basin		80,487		64,920		7,150
Permian Basin		44,955		83,823		56,020
Piceance Basin		1,946		7,887		16,564
Barnett Shale (2)		184		1,370		569
Marcellus Shale		693		1,030		641
Total reportable segment capital expenditures		163,028		189,951		121,174
Corporate and Other		19,263		10,635		3,041
Total cash paid for capital expenditures	$	182,291	$	200,586	$	124,215

(1)	Excludes cash paid for capital expenditures by Ohio Gathering due to equity method accounting.

(2)	For the year ended December 31, 2019, the amount includes sales tax reimbursements of $1.1 million.

Schedule of counterparties accounting for more than 10% of total revenues

Counterparties accounting for more than 10% of total revenues were as follows:

	Year ended December 31,
	2019			2018			2017
Percentage of total revenues (1):
Counterparty A - Piceance Basin		11	%	*			*
Counterparty B - Williston Basin		10	%	*				13	%
Counterparty C - Piceance Shale	*				10	%	*
Counterparty D - Barnett Shale	*			*			*

(1) Excludes revenues earned by Ohio Gathering due to equity method accounting.

* Less than 10%

Reconciliation of net income to adjusted EBITDA

Segment adjusted EBITDA by reportable segment follows.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	29,292		$	30,285		$	34,011
Ohio Gathering		39,126			39,969			41,246
Williston Basin		69,437			76,701			66,413
DJ Basin		18,668			7,558			6,624
Permian Basin		(879	)		(1,200	)		—
Piceance Basin		98,765			111,042			111,113
Barnett Shale		43,043			43,268			46,232
Marcellus Shale		20,051			24,267			23,888
Total of reportable segments' measures of profit	$	317,503		$	331,890		$	329,527

A reconciliation of income or loss before income taxes and income or loss from equity method investees to total of reportable segments' measures of profit or loss follows.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Reconciliation of (loss) income before income taxes and loss from equity method investees to total of reportable segments' measures of profit:
(Loss) income before income taxes and loss from equity method investees	$	(30,808	)	$	53,272		$	88,614
Add:
Corporate and Other expense		40,639			38,917			39,140
Interest expense		74,429			60,535			68,131
Early extinguishment of debt		—			—			22,039
Deferred Purchase Price Obligation		(1,982	)		20,975			(200,322	)
Depreciation and amortization		111,426			106,767			114,872
Proportional adjusted EBITDA for equity method investees		39,126			39,969			41,246
Adjustments related to MVC shortfall payments		3,476			(3,632	)		(41,373	)
Adjustments related to capital reimbursement activity		(2,156	)		(427	)		—
Unit-based and noncash compensation		8,171			8,328			7,951
(Gain) loss on asset sales, net		(1,536	)		—			527
Long-lived asset impairment		60,507			7,186			188,702
Goodwill impairment		16,211			—			—
Total of reportable segments' measures of profit	$	317,503		$	331,890		$	329,527

Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments

Adjustments related to MVC shortfall payments by reportable segment follow.

	Year ended December 31, 2019
	Williston Basin		Piceance Basin			Barnett Shale		Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	—	$	(103	)	$	3,579	$	3,476

	Year ended December 31, 2018
	Williston Basin		Piceance Basin		Barnett Shale			Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	—	$	10	$	(3,642	)	$	(3,632	)

	Year Ended December 31, 2017
	Williston Basin			Piceance Basin			Barnett Shale			Total
	(In thousands)
Adjustments related to MVC shortfall payments:
Net change in deferred revenue for MVC shortfall payments	$	(37,693	)	$	(3,065	)	$	—		$	(40,758	)
Expected MVC shortfall adjustments		—			(3	)		(612	)		(615	)
Total adjustments related to MVC shortfall payments	$	(37,693	)	$	(3,068	)	$	(612	)	$	(41,373	)

EARNINGS PER UNIT

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

EARNINGS PER UNIT

13. EARNINGS PER UNIT

The following table details the components of EPU.

	Year ended December 31,
	2019			2018		2017
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net (loss) income among limited partner interests:
Net (loss) income attributable to limited partners	$	(369,845	)	$	32,799	$	75,485
Less net income attributable to Series A Preferred Units		28,500			28,500		3,563
Less net income attributable to Subsidiary Series A Preferred Units		58			—		—
Net (loss) income attributable to common limited partners	$	(398,403	)	$	4,299	$	71,922

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic		82,365			73,304		72,705
Effect of nonvested phantom units		—			311		342
Weighted-average common units outstanding – diluted		82,365			73,615		73,047

(Loss) earnings per limited partner unit:
Common unit – basic	$	(4.84	)	$	0.06	$	0.99
Common unit – diluted	$	(4.84	)	$	0.06	$	0.98

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		175			2		42

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Total long-term debt	$ 1,470,299	$ 1,257,731
SMP Holdings
Line of Credit Facility [Line Items]
Total long-term debt	1,470,299	1,257,731
SMP Holdings \| Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility	677,000	466,000
SMP Holdings \| Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Unsecured notes	300,000	300,000
Less unamortized debt issuance costs	(1,686)	(2,362)
SMP Holdings \| Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Unsecured notes	500,000	500,000
Less unamortized debt issuance costs	$ (5,015)	$ (5,907)

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Lease Cost and Other Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Lease cost
Amortization of ROU assets (included in depreciation and amortization)	$ 1,559
Interest on lease liabilities (included in interest expense)	102
Operating lease cost (included in general and administrative expense)	3,159
Total lease cost	4,820
Other information
Operating cash outflows from operating leases	3,396
Operating cash outflows from finance leases	102
Financing cash outflows from finance leases	1,873
ROU assets obtained in exchange for new operating lease liabilities	1,218
ROU assets obtained in exchange for new finance lease liabilities	$ 1,350
Weighted-average remaining lease term (years) - operating leases	5 years 9 months 18 days
Weighted-average remaining lease term (years) - finance leases	2 years
Weighted-average discount rate - operating leases	5.00%
Weighted-average discount rate - finance leases	4.00%

CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Dec. 31, 2019	Dec. 31, 2018
Subsidiary Series A preferred unitholders, issued	300,000	300,000
Subsidiary Series A preferred unitholders, outstanding	300,000	300,000
Common limited partner capital (in shares), issued	93,493,473	73,390,853
Common limited partner capital (in shares), outstanding	93,493,473	73,390,853
General partner interests (in shares), issued	0	1,490,999
General partner interests (in shares), outstanding	0	1,490,999
Mezzanine Capital
Subsidiary Series A preferred unitholders, issued	30,058
Subsidiary Series A preferred unitholders, outstanding	30,058

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Cash Flows [Abstract]
Net of cash	$ 1,475
Cash and cash equivalents	4,948	$ 4,345	$ 1,430
Restricted cash	27,392
Total cash, cash equivalents and restricted cash	$ 32,340	$ 4,345	$ 1,430

FINANCIAL INSTRUMENTS (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of the estimated fair value of debt instruments

A summary of the estimated fair value of our debt financial instruments follows.

	December 31, 2019				December 31, 2018
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Summit Holdings 5.5% Senior Notes ($300.0 million principal)	$	298,314	$	266,750	$	297,638	$	286,625
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		494,985		382,708		494,093		455,208

CONDENSED CONSOLIDATING FINANCIAL INFORMATION

12 Months Ended

Dec. 31, 2019

Condensed Consolidating Financial Information [Abstract]

CONDENSED CONSOLIDATING FINANCIAL INFORMATION

18. CONDENSED CONSOLIDATING FINANCIAL INFORMATION

The Senior Notes are fully and unconditionally guaranteed, jointly and severally, on a senior unsecured basis by SMLP and the Guarantor Subsidiaries (see Note 10).

In December 2019, as part of our financing for the Double E Project, we formed Permian Holdco, a newly created, unrestricted subsidiary of SMLP that indirectly owns SMLP’s 70% interest in Double E. In December 2019, we executed the third amendment to the third amended and restated credit agreement that, among other things, designated Permian Holdco and Summit Permian Transmission as unrestricted subsidiaries under the Revolving Credit Facility. Prior to this amendment, Summit Permian Transmission did not have any assets or operations. In December 2019, we executed a partial release agreement that designated the Non-Guarantor Subsidiaries as unrestricted subsidiaries under the Senior Notes. As a result of these transactions, all prior periods presented have been recast to reflect this change.

The following supplemental condensed consolidating financial information reflects SMLP's separate accounts, the combined accounts of the Co-Issuers, the combined accounts of the Guarantor Subsidiaries, the combined accounts of the Non-Guarantor Subsidiaries and the consolidating adjustments for the dates and periods indicated. For purposes of the following consolidating information each of SMLP and the Co-Issuers account for their subsidiary investments, if any, under the equity method of accounting.

Condensed Consolidating Balance Sheet. Balance sheets as of December 31, 2019 and 2018 follow.

	December 31, 2019
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	118	$	611	$	4,110	$	109	$	—		$	4,948
Restricted cash		—		—		—		27,392		—			27,392
Accounts receivable		69		—		102,049		—		—			102,118
Other current assets		2,124		—		2,894		—		—			5,018
Due from affiliate		—		36,300		776,552		—		(812,852	)		—
Total current assets		2,311		36,911		885,605		27,501		(812,852	)		139,476
Property, plant and equipment, net		6,420		—		1,875,558		—		273			1,882,251
Intangible assets, net		—		—		232,278		—		—			232,278
Investment in equity method investees		—		—		275,000		35,002		(274	)		309,728
Other noncurrent assets		3,152		6,167		29		370		—			9,718
Investment in subsidiaries		1,758,547		3,198,079		—		—		(4,956,626	)		—
Total assets	$	1,770,430	$	3,241,157	$	3,268,470	$	62,873	$	(5,769,479	)	$	2,573,451

Liabilities and Capital
Trade accounts payable	$	657	$	—	$	23,758	$	—	$	—		$	24,415
Accrued expenses		1,649		—		9,536		297		—			11,482
Due to affiliate		777,077		—		—		—		(776,766	)		311
Deferred revenue		—		—		13,493		—		—			13,493
Ad valorem taxes payable		14		—		8,463				—			8,477
Accrued interest		—		12,311		—		—		—			12,311
Accrued environmental remediation		—		—		1,725		—		—			1,725
Other current liabilities		7,342		—		4,591				—			11,933
Total current liabilities		786,739		12,311		61,566		297		(776,766	)		84,147
Long-term debt		—		1,470,299		—		—		—			1,470,299
Noncurrent Deferred Purchase Price Obligation		178,453		—		—		—		—			178,453
Noncurrent deferred revenue		—		—		38,709		—		—			38,709
Noncurrent accrued environmental remediation		—		—		2,926		—		—			2,926
Other noncurrent liabilities		5,635		—		2,316		—		—			7,951
Total liabilities		970,827		1,482,610		105,517		297		(776,766	)		1,782,485

Total mezzanine capital		—		—		—		27,450		—			27,450

Total partners' capital		799,603		1,758,547		3,162,953		35,126		(4,992,713	)		763,516
Total liabilities, mezzanine capital and partners' capital	$	1,770,430	$	3,241,157	$	3,268,470	$	62,873	$	(5,769,479	)	$	2,573,451

	December 31, 2018
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	185	$	230	$	3,930	$	—	$	—		$	4,345
Accounts receivable		321		—		97,615		—		—			97,936
Other current assets		1,179		—		2,792		—		—			3,971
Due from affiliate		—		—		593,384		—		(593,384	)		—
Total current assets		1,685		230		697,721		—		(593,384	)		106,252
Property, plant and equipment, net		5,813		—		1,948,280		9,620		—			1,963,713
Intangible assets, net		—		—		273,416		—		—			273,416
Goodwill		—		—		16,211		—		—			16,211
Investment in equity method investees		—		—		649,250		—		—			649,250
Other noncurrent assets		3,183		8,511		26		—		—			11,720
Investment in subsidiaries		2,096,717		3,461,921		—		—		(5,558,638	)		—
Total assets	$	2,107,398	$	3,470,662	$	3,584,904	$	9,620	$	(6,152,022	)	$	3,020,562

Liabilities and Partners' Capital
Trade accounts payable	$	275	$	—	$	35,831	$	2,308	$	—		$	38,414
Accrued expenses		1,106		—		20,857		—		—			21,963
Due to affiliate		482,384		103,928		—		—		(586,072	)		240
Deferred revenue		—		—		11,467		—		—			11,467
Ad valorem taxes payable		14		—		10,536		—		—			10,550
Accrued interest		—		12,286		—		—		—			12,286
Accrued environmental remediation		—		—		2,487		—		—			2,487
Other current liabilities		7,306		—		5,339		—		—			12,645
Total current liabilities		491,085		116,214		86,517		2,308		(586,072	)		110,052
Long-term debt		—		1,257,731		—		—		—			1,257,731
Noncurrent Deferred Purchase Price Obligation		383,934		—		—		—		—			383,934
Noncurrent deferred revenue		—		—		39,504		—		—			39,504
Noncurrent accrued environmental remediation		—		—		3,149		—		—			3,149
Other noncurrent liabilities		3,843		—		1,125		—		—			4,968
Total liabilities		878,862		1,373,945		130,295		2,308		(586,072	)		1,799,338

Total partners' capital		1,228,536		2,096,717		3,454,609		7,312		(5,565,950	)		1,221,224
Total liabilities partners' capital	$	2,107,398	$	3,470,662	$	3,584,904	$	9,620	$	(6,152,022	)	$	3,020,562

Condensed Consolidating Statement of Operations. For the purposes of the following condensed consolidating statements of operations, we allocate general and administrative expenses recognized at the SMLP parent to the Guarantor Subsidiaries and Non-Guarantor Subsidiaries to reflect what those entities' results would have been had they operated on a stand-alone basis. Statements of operation for the years ended December 31, 2019, 2018 and 2017 follow.

	Year ended December 31, 2019
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments		Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	326,747					$	—	$	326,747
Natural gas, NGLs and condensate sales		—			—			86,994			—			—		86,994
Other revenues		—			—			29,787						—		29,787
Total revenues		—			—			443,528			—			—		443,528
Costs and expenses:
Cost of natural gas and NGLs		—			—			63,438			—			—		63,438
Operation and maintenance		—			—			97,587			—			—		97,587
General and administrative		—			—			54,139			—			—		54,139
Depreciation and amortization		2,604			—			107,602			—			—		110,206
Transaction costs		1,788			—			—			—			—		1,788
Loss (gain) on asset sales, net		9			—			(1,545	)		—			—		(1,536	)
Long-lived asset impairment		—			—			60,507			—			—		60,507
Goodwill impairment		—			—			16,211			—			—		16,211
Total costs and expenses		4,401			—			397,939			—			—		402,340
Other income		451			—			—			—			—		451
Interest expense		—			(74,327	)		(102	)		—			—		(74,429	)
Deferred Purchase Price Obligation		1,982			—			—			—			—		1,982
(Loss) income before income taxes and loss from equity method investees		(1,968	)		(74,327	)		45,487			—			—		(30,808	)
Income tax expense		(1,174	)		—			—			—			—		(1,174	)
Loss from equity method investees		—			—			(336,950	)		(901	)		—		(337,851	)
Equity in earnings of consolidated subsidiaries		(366,691	)		(292,364	)		—			—			659,055		—
Net (loss) income	$	(369,833	)	$	(366,691	)	$	(291,463	)	$	(901	)	$	659,055	$	(369,833	)

	Year ended December 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	344,616		$	—	$	—		$	344,616
Natural gas, NGLs and condensate sales		—			—			134,834			—		—			134,834
Other revenues		—			—			27,203			—		—			27,203
Total revenues		—			—			506,653			—		—			506,653
Costs and expenses:
Cost of natural gas and NGLs		—			—			107,661			—		—			107,661
Operation and maintenance		—			—			96,878			—		—			96,878
General and administrative		—			—			52,877			—		—			52,877
Depreciation and amortization		1,743			—			105,357			—		—			107,100
Long-lived asset impairment		—			—			7,186			—		—			7,186
Total costs and expenses		1,743			—			369,959			—		—			371,702
Other income		(169	)		—			—			—		—			(169	)
Interest expense		—			(60,442	)		(93	)		—		—			(60,535	)
Deferred Purchase Price Obligation		(20,975	)		—			—			—		—			(20,975	)
Income (loss) before income taxes and loss from equity method investees		(22,887	)		(60,442	)		136,601			—		—			53,272
Income tax expense		(33	)		—			—			—		—			(33	)
Loss from equity method investees		—			—			(10,888	)		—		—			(10,888	)
Equity in earnings of consolidated subsidiaries		65,271			125,713			—			—		(190,984	)		—
Net income	$	42,351		$	65,271		$	125,713		$	—	$	(190,984	)	$	42,351

	Year ended December 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments		Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	394,427		$	—	$	—	$	394,427
Natural gas, NGLs and condensate sales		—			—			68,459			—		—		68,459
Other revenues		—			—			25,855			—		—		25,855
Total revenues		—			—			488,741			—		—		488,741
Costs and expenses:
Cost of natural gas and NGLs		—			—			57,237			—		—		57,237
Operation and maintenance		—			—			93,882			—		—		93,882
General and administrative		—			—			54,681			—		—		54,681
Depreciation and amortization		1,101			—			114,374			—		—		115,475
Transaction costs		73			—			—			—		—		73
Gain on asset sales, net		—			—			527			—		—		527
Long-lived asset impairment		—			—			188,702			—		—		188,702
Total costs and expenses		1,174			—			509,403			—		—		510,577
Other income		298			—			—			—		—		298
Interest expense		—			(68,080	)		(51	)		—		—		(68,131	)
Early extinguishment of debt		—			(22,039	)		—			—		—		(22,039	)
Deferred Purchase Price Obligation		200,322			—			—			—		—		200,322
Loss before income taxes and loss from equity method investees		199,446			(90,119	)		(20,713	)		—		—		88,614
Income tax expense		(341	)		—			—			—		—		(341	)
Loss from equity method investees		—			—			(2,223	)		—		—		(2,223	)
Equity in loss of consolidated subsidiaries		(113,055	)		(22,936	)		—			—		135,991		—
Net loss	$	86,050		$	(113,055	)	$	(22,936	)	$	—	$	135,991	$	86,050

Condensed Consolidating Statement of Cash Flows. Statement of cash flows for the years ended December 31, 2019, 2018 and 2017 follow.

	Year ended December 31, 2019
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	5,811		$	(69,891	)	$	246,492		$	(75	)	$	—		$	182,337

Cash flows from investing activities:
Capital expenditures		(1,323	)		—			(163,379	)		(17,589	)		—			(182,291	)
Proceeds from asset sales		—			—			102,111			—			—			102,111
Distributions from equity method investment		—			—			—			7,313			—			7,313
Investment in equity method investee		—			—			—			(18,316	)		—			(18,316	)
Other, net		314			—			(1	)		—			—			313
Advances to affiliates		(28,776	)		(140,229	)		(183,170	)		—			352,175			—
Net cash (used in) provided by investing activities		(29,785	)		(140,229	)		(244,439	)		(28,592	)		352,175			(90,870	)

Cash flows from financing activities:
Distributions to unitholders		(116,624	)		—			—			—			—			(116,624	)
Distributions to Series A Preferred unitholders		(28,500	)		—			—			—			—			(28,500	)
Borrowings under Revolving Credit Facility		—			369,000			—			—			—			369,000
Repayments under Revolving Credit Facility		—			(158,000	)		—			—			—			(158,000	)
Repayment of Deferred Purchase Price Obligation		(151,750	)		—			—			—			—			(151,750	)
Debt issuance costs		—			(499	)		—			—			—			(499	)
Proceeds from the issuance of Series A preferred units, net of costs		—			—			—			27,392			—			27,392
Other, net		(2,618	)		—			(1,873	)					—			(4,491	)
Advances from affiliates		323,399			—			—			28,776			(352,175	)		—
Net cash (used in) provided by financing activities		23,907			210,501			(1,873	)		56,168			(352,175	)		(63,472	)
Net change in cash, cash equivalents and restricted cash		(67	)		381			180			27,501			—			27,995
Cash, cash equivalents and restricted cash, beginning of period		185			230			3,930			—			—			4,345
Cash, cash equivalents and restricted cash, end of period	$	118		$	611		$	4,110		$	27,501		$	—		$	32,340

	Year ended December 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	7,470		$	(56,181	)	$	276,640		$	—		$	—		$	227,929

Cash flows from investing activities:
Capital expenditures		(3,323	)		—			(189,951	)		(7,312	)		—			(200,586	)
Proceeds from asset sales		—			—			496			—			—			496
Contributions to equity method investees		—			—			(4,924	)		—			—			(4,924	)
Purchase of noncontrolling interest		(10,981	)		—			—			—			—			(10,981	)
Other, net		(284	)		—			—			—			—			(284	)
Advances to affiliates		(7,312	)		(148,320	)		(78,287	)		—			233,919			—
Net cash provided by (used in) investing activities		(21,900	)		(148,320	)		(272,666	)		(7,312	)		233,919			(216,279	)

Cash flows from financing activities:
Distributions to unitholders		(180,705	)		—			—			—			—			(180,705	)
Distributions to Series A Preferred unitholders		(28,500	)		—			—			—			—			(28,500	)
Borrowings under Revolving Credit Facility		—			289,000			—			—			—			289,000
Repayments under Revolving Credit Facility		—			(84,000	)		—			—			—			(84,000	)
Debt issuance costs		—			(344	)		—			—			—			(344	)
Other, net		(2,913	)		—			(1,273	)		—			—			(4,186	)
Advances from affiliates		226,607			—			—			7,312			(233,919	)		—
Net cash (used in) provided by financing activities		14,489			204,656			(1,273	)		7,312			(233,919	)		(8,735	)
Net change in cash and cash equivalents		59			155			2,701			—			—			2,915
Cash and cash equivalents, beginning of period		126			75			1,229			—			—			1,430
Cash and cash equivalents, end of period	$	185		$	230		$	3,930		$	—		$	—		$	4,345

	Year ended December 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$	7,122		$	(68,915	)	$	299,625		$	—	$	—		$	237,832

Cash flows from investing activities:
Capital expenditures		(3,041	)		—			(121,174	)		—		—			(124,215	)
Proceeds from asset sales		—			—			2,300			—		—			2,300
Contributions to equity method investees		—			—			(25,513	)		—		—			(25,513	)
Purchase of noncontrolling interest		(797	)		—			—			—		—			(797	)
Other, net		(458	)		—			—			—		—			(458	)
Advances to affiliates		(278,493	)		—			(148,229	)		—		426,722			—
Net cash used in investing activities		(282,789	)		—			(292,616	)		—		426,722			(148,683	)

Cash flows from financing activities:
Distributions to unitholders		(179,103	)		—			—			—		—			(179,103	)
Distributions to Series A Preferred unitholders		(2,375	)		—			—			—		—			(2,375	)
Borrowings under Revolving Credit Facility		—			247,500			—			—		—			247,500
Repayments under Revolving Credit Facility		—			(634,500	)		—			—		—			(634,500	)
Debt issuance costs		—			(16,390	)		—			—		—			(16,390	)
Payment of redemption and call premiums on senior notes		—			(17,932	)		—			—		—			(17,932	)
Proceeds from ATM Program issuances, net of costs		17,078			—			—			—		—			17,078
Proceeds from issuance of Series A preferred units, net of costs		293,238			—			—			—		—			293,238
Contribution from General Partner		465			—			—			—		—			465
Issuance of senior notes		—			500,000			—			—		—			500,000
Tender and redemption of senior notes		—			(300,000	)		—			—		—			(300,000	)
Other, net		(2,437	)		—			(691	)		—		—			(3,128	)
Advances from affiliates		148,229			290,261			(11,768	)		—		(426,722	)		—
Net cash provided by (used in) financing activities		275,095			68,939			(12,459	)		—		(426,722	)		(95,147	)
Net change in cash and cash equivalents		(572	)		24			(5,450	)		—		—			(5,998	)
Cash and cash equivalents, beginning of period		698			51			6,679			—		—			7,428
Cash and cash equivalents, end of period	$	126		$	75		$	1,229		$	—	$	—		$	1,430

AMORTIZING INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible assets and liabilities subject to amortization

Details regarding our intangible assets, all of which are subject to amortization, follow.

	December 31, 2019
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(15,125	)	$	9,070
Contract intangibles		278,448		(169,549	)		108,899
Rights-of-way		157,175		(42,866	)		114,309
Total intangible assets	$	459,818	$	(227,540	)	$	232,278

	December 31, 2018
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(13,905	)	$	10,290
Contract intangibles		278,448		(143,962	)		134,486
Rights-of-way		166,209		(37,569	)		128,640
Total intangible assets	$	468,852	$	(195,436	)	$	273,416

Recognized amortization expense in other revenues and cost and expenses

We recognized amortization expense in Other revenues as follows:

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(1,220	)	$	(1,555	)	$	(1,555	)

We recognized amortization expense in costs and expenses as follows:

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Amortization expense – contract intangibles	$	25,587	$	26,141	$	34,202
Amortization expense – rights-of-way		6,278		6,448		6,153

Estimated aggregate annual amortization expected to be recognized

The estimated aggregate annual amortization expected to be recognized for as of December 31, 2019 for each of the five succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2020	$	31,901
2021		28,209
2022		25,142
2023		25,088
2024		14,917

DEBT

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

DEBT

10. DEBT

Debt consisted of the following:

	December 31, 2019			December 31, 2018
	(In thousands)
Summit Holdings' variable rate senior secured Revolving Credit Facility (4.55% at December 31, 2019 and 5.03% at December 31, 2018) due May 2022	$	677,000		$	466,000
Summit Holdings' 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(1,686	)		(2,362	)
Summit Holdings' 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(5,015	)		(5,907	)
Total long-term debt	$	1,470,299		$	1,257,731

(1) Issuance costs are being amortized over the life of the notes.

The aggregate amount of debt maturing during each of the years after December 31, 2019 are as follows (in thousands):

2020	$	—
2021		—
2022		977,000
2023		—
2024		—
Thereafter		500,000
Total long-term debt	$	1,477,000

Revolving Credit Facility. Summit Holdings has a senior secured revolving credit facility which allows for revolving loans, letters of credit and swingline loans. The Revolving Credit Facility has a $1.25 billion borrowing capacity, matures in May 2022, and includes a $250.0 million accordion feature. As of December 31, 2019, SMLP and the Guarantor Subsidiaries fully and unconditionally and jointly and severally guarantee, and pledge substantially all of their assets in support of, the indebtedness outstanding under the Revolving Credit Facility.

In May 2017, Summit Holdings amended and restated its Revolving Credit Facility with a third amended and restated credit agreement which: (i) maintained the Revolving Credit Facility commitments of $1.25 billion, (ii) extended the maturity from November 2018 to May 2022, (iii) included a $250.0 million accordion feature, (iv) maintained the same leverage-based pricing and commitment fee grid, (v) increased the maximum permitted total leverage ratio, as defined in the credit agreement, from 5.00 to 1.00 to 5.50 to 1.00 and (vi) included a maximum permitted senior secured leverage ratio, as defined in the credit agreement, of 3.75 to 1.00. In June 2019, we executed the second amendment to the third amended and restated credit agreement that, among other things, made accommodations for the transactions contemplated by the Agreement and designated Double E as an unrestricted subsidiary under the Revolving Credit Facility. In December 2019, we executed the third amendment to the third amended and restated credit agreement that, among other things, designated the Non-Guarantor Subsidiaries as unrestricted subsidiaries under the Revolving Credit Facility.

Borrowings under the Revolving Credit Facility bear interest, at the election of Summit Holdings, at a rate based on the alternate base rate (as defined in the credit agreement) plus an applicable margin ranging from 0.75% to 1.75% or the adjusted Eurodollar rate (as defined in the credit agreement) plus an applicable margin ranging from 1.75% to 2.75%, with the commitment fee ranging from 0.30% to 0.50% in each case based on our relative leverage at the time of determination. At December 31, 2019, the applicable margin under LIBOR borrowings was 2.75%, the interest rate was 4.55% and the unused portion of the Revolving Credit Facility totaled $563.9 million, subject to a commitment fee of 0.50%, after giving effect to the issuance thereunder of a $9.1 million outstanding but undrawn irrevocable standby letter of credit. Based on covenant limits, our available borrowing capacity under the Revolving Credit Facility as of December 31, 2019 was approximately $100 million. See Note 16 for additional information on our letter of credit.

The Revolving Credit Facility is secured by the membership interests of Summit Holdings and the membership interests of the Guarantor Subsidiaries of Summit Holdings and by substantially all of the assets of Summit Holdings and its Guarantor Subsidiaries (subject to exclusions set forth in the credit agreement). The credit agreement contains affirmative and negative covenants customary for credit facilities of its size and nature that, among other things, limit or restrict the ability (i) to incur additional debt; (ii) to make investments; (iii) to engage in certain mergers, consolidations, acquisitions or sales of assets; (iv) to enter into swap agreements and power purchase agreements; (v) to enter into leases that would cumulatively obligate payments in excess of $50.0 million over any 12 -month period; and (vi) of Summit Holdings to make distributions, with certain exceptions, including the distribution of Available Cash (as defined in the SMLP Partnership Agreement) if no default or event of default then exists or would result therefrom and Summit Holdings is in pro forma compliance with its financial covenants. In addition, the Revolving Credit Facility requires Summit Holdings to maintain (i) a ratio of consolidated trailing 12 -month earnings before interest, income taxes, depreciation and amortization ("EBITDA") to net interest expense of not less than 2.5 to 1.0 as defined in the credit agreement, (ii) a ratio of total net indebtedness to consolidated trailing 12 -month EBITDA of not more than 5.50 to 1.00 and, (iii) a ratio of first lien net indebtedness to consolidated trailing 12 -month EBITDA of not more than 3.75 to 1.00.

As of December 31, 2019, we had $6.2 million of debt issuance costs attributable to our Revolving Credit Facility and related amendments which are included in Other noncurrent assets on the consolidated balance sheet.

As of December 31, 2019, we were in compliance with the Revolving Credit Facility's financial covenants. There were no defaults or events of default during the year ended December 31, 2019.

Senior Notes. In July 2014, Summit Holdings and its 100% owned finance subsidiary, Finance Corp. (together with Summit Holdings, the "Co-Issuers") co-issued $300.0 million of 5.5% senior unsecured notes maturing August 15, 2022 (the "5.5% Senior Notes" and, together with the 5.75% Senior Notes (defined below), the “Senior Notes”).

In 2018, we executed supplemental indentures to include OpCo, Summit Utica, Meadowlark Midstream and Tioga Midstream (through March 22, 2019) as guarantors concurrent with the purchase of a 1% noncontrolling interest held by a subsidiary of Summit Investments (see Note 12 to the consolidated financial statements for additional details). In 2019, we executed a partial release agreement that designated the Non-Guarantor Subsidiaries as unrestricted subsidiaries under the Senior Notes.

The Guarantor Subsidiaries are 100% owned by a subsidiary of SMLP. The Guarantor Subsidiaries and SMLP fully and unconditionally and jointly and severally guarantee the Senior Notes. There are no significant restrictions on the ability of SMLP or Summit Holdings to obtain funds from its subsidiaries by dividend or loan. Finance Corp. has had no assets or operations since inception in 2013. We have no other independent assets or operations. At no time have the Senior Notes been guaranteed by the Co-Issuers.

5.75% Senior Notes. In February 2017, the Co-Issuers completed a public offering of $500.0 million of 5.75% senior unsecured notes maturing April 15, 2025. We pay interest on the 5.75% Senior Notes semi-annually in cash in arrears on April 15 and October 15 of each year. The 5.75% Senior Notes are senior, unsecured obligations and rank equally in right of payment with all of our existing and future senior obligations. The 5.75% Senior Notes are effectively subordinated in right of payment to all of our secured indebtedness, to the extent of the collateral securing such indebtedness. We used the proceeds from the issuance of the 5.75% Senior Notes to (i) fund the repurchase of the outstanding $300.0 million principal 7.5% Senior Notes, (ii) pay redemption and call premiums on the 7.5% Senior Notes totaling $17.9 million and (iii) pay $172.0 million of the balance outstanding under our Revolving Credit Facility.

At any time prior to April 15, 2020, the Co-Issuers may redeem up to 35% of the aggregate principal amount of the 5.75% Senior Notes at a redemption price of 105.750% of the principal amount of the 5.75% Senior Notes, plus accrued and unpaid interest, if any, but not including, the redemption date, with an amount not greater than the net cash proceeds of certain equity offerings. On and after April 15, 2020, the Co-Issuers may redeem all or part of the 5.75% Senior Notes at a redemption price of 104.313% (with the redemption premium declining ratably each year to 100.000% on and after April 15, 2023), plus accrued and unpaid interest, if any, to, but not including, the redemption date. Debt issuance costs of $7.7 million are being amortized over the life of the 5.75% Senior Notes.

The 5.75% Senior Notes' indenture restricts SMLP’s and the Co-Issuers’ ability and the ability of certain of their subsidiaries to: (i) incur additional debt or issue preferred stock; (ii) make distributions, repurchase equity or redeem subordinated debt; (iii) make payments on subordinated indebtedness; (iv) create liens or other encumbrances; (v) make investments, loans or other guarantees; (vi) sell or otherwise dispose of a portion of their assets; (vii) engage in transactions with affiliates; and (viii) make acquisitions or merge or consolidate with another entity. These covenants are subject to a number of important exceptions and qualifications. At any time when the senior notes are rated investment grade by each of Moody’s Investors Service, Inc. and Standard & Poor’s Ratings Services and no default or event of default under the indenture has occurred and is continuing, many of these covenants will terminate.

The 5.75% Senior Notes' indenture provides that each of the following is an event of default: (i) default for 30 days in the payment when due of interest on the 5.75% Senior Notes; (ii) default in the payment when due of the principal of, or premium, if any, on the 5.75% Senior Notes; (iii) failure by the Co-Issuers or SMLP to comply with certain covenants relating to mergers and consolidations, change of control or asset sales; (iv) failure by SMLP for 180 days after notice to comply with certain covenants relating to the filing of reports with the SEC; (v) failure by the Co-Issuers or SMLP for 30 days after notice to comply with any of the other agreements in the indenture; (vi) specified defaults under any mortgage, indenture or instrument under which there may be issued or by which there may be secured or evidenced any indebtedness for money borrowed by SMLP or any of its restricted subsidiaries (or the payment of which is guaranteed by SMLP or any of its restricted subsidiaries); (vii) failure by SMLP or any of its restricted subsidiaries to pay certain final judgments aggregating in excess of $75.0 million; (viii) except as permitted by the indenture, any guarantee of the senior notes shall cease for any reason to be in full force and effect or any guarantor, or any person acting on behalf of any guarantor, shall deny or disaffirm its obligations under its guarantee of the senior notes; and (ix) certain events of bankruptcy, insolvency or reorganization described in the indenture. In the case of an event of default as described in the foregoing clause (ix), all outstanding 5.75% Senior Notes will become due and payable immediately without further action or notice. If any other event of default occurs and is continuing, the trustee or the holders of at least 25% in principal amount of the then outstanding 5.75% Senior Notes may declare all the 5.75% Senior Notes to be due and payable immediately.

5.5% Senior Notes. We pay interest on the 5.5% Senior Notes semi-annually in cash in arrears on February 15 and August 15 of each year. The 5.5% Senior Notes are senior, unsecured obligations and rank equally in right of payment with all of our existing and future senior obligations. The 5.5% Senior Notes are effectively subordinated in right of payment to all of our secured indebtedness, to the extent of the collateral securing such indebtedness. We used the proceeds from the issuance of the 5.5% Senior Notes to repay a portion of the balance outstanding under our Revolving Credit Facility.

At any time prior to August 15, 2020, the Co-Issuers may redeem all or part of the 5.5% Senior Notes at a redemption price of 101.375% (with the redemption premium declining to 100.000% on and after August 15, 2020), plus accrued and unpaid interest, if any. Debt issuance costs of $5.1 million are being amortized over the life of the 5.5% Senior Notes.

The 5.5% Senior Notes' indenture restricts SMLP’s and the Co-Issuers’ ability and the ability of certain of their subsidiaries to: (i) incur additional debt or issue preferred stock; (ii) make distributions, repurchase equity or redeem subordinated debt; (iii) make payments on subordinated indebtedness; (iv) create liens or other encumbrances; (v) make investments, loans or other guarantees; (vi) sell or otherwise dispose of a portion of their assets; (vii) engage in transactions with affiliates; and (viii) make acquisitions or merge or consolidate with another entity. These covenants are subject to a number of important exceptions and qualifications. At any time when the senior notes are rated investment grade by each of Moody’s Investors Service, Inc. and Standard & Poor’s Ratings Services and no default or event of default under the indenture has occurred and is continuing, many of these covenants will terminate.

The 5.5% Senior Notes' indenture provides that each of the following is an event of default: (i) default for 30 days in the payment when due of interest on the 5.5% Senior Notes; (ii) default in the payment when due of the principal of, or premium, if any, on the 5.5% Senior Notes; (iii) failure by the Co-Issuers or SMLP to comply with certain covenants relating to mergers and consolidations, change of control or asset sales; (iv) failure by SMLP for 180 days after notice to comply with certain covenants relating to the filing of reports with the SEC; (v) failure by the Co-Issuers or SMLP for 30 days after notice to comply with any of the other agreements in the indenture; (vi) specified defaults under any mortgage, indenture or instrument under which there may be issued or by which there may be secured or evidenced any indebtedness for money borrowed by SMLP or any of its restricted subsidiaries (or the payment of which is guaranteed by SMLP or any of its restricted subsidiaries); (vii) failure by SMLP or any of its restricted subsidiaries to pay certain final judgments aggregating in excess of $20.0 million; (viii) except as permitted by the indenture, any guarantee of the senior notes shall cease for any reason to be in full force and effect or any guarantor, or any person acting on behalf of any guarantor, shall deny or disaffirm its obligations under its guarantee of the senior notes; and (ix) certain events of bankruptcy, insolvency or reorganization described in the indenture. In the case of an event of default as described in the foregoing clause (ix), all outstanding 5.5% Senior Notes will become due and payable immediately without further action or notice. If any other event of default occurs and is continuing, the trustee or the holders of at least 25% in principal amount of the then outstanding 5.5% Senior Notes may declare all the 5.5% Senior Notes to be due and payable immediately.

As of and during the December 31, 2019, we were in compliance with the financial covenants governing our Senior Notes. There were no defaults or events of default during the year ended December 31, 2019.

UNAUDITED QUARTERLY FINANCIAL DATA

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

UNAUDITED QUARTERLY FINANCIAL DATA

19. UNAUDITED QUARTERLY FINANCIAL DATA

Summarized information on the consolidated results of operations for each of the quarters during the two-year period ended December 31, 2019, follows.

	Quarter ended
	December 31, 2019			September 30, 2019			June 30, 2019			March 31, 2019
	(In thousands, except per-unit amounts)
Total revenues	$	112,247		$	100,187		$	99,686		$	131,408

Net (loss) income attributable to SMLP	$	(327,083	)	$	(10,645	)	$	4,809		$	(36,914	)
Less net income and IDRs attributable to General Partner		—			—			—			12
Less net income attributable to Series A Preferred Units		7,125			7,125			7,125			7,125
Less net income attributable to Subsidiary Series A Preferred Units		58			—			—			—
Net loss attributable to common limited partners	$	(334,266	)	$	(17,770	)	$	(2,316	)	$	(44,051	)

Loss per limited partner unit:
Common unit - basic	$	(3.79	)	$	(0.21	)	$	(0.03	)	$	(0.58	)
Common unit - diluted	$	(3.79	)	$	(0.21	)	$	(0.03	)	$	(0.58	)

	Quarter ended
	December 31, 2018		September 30, 2018		June 30, 2018			March 31, 2018
	(In thousands, except per-unit amounts)
Total revenues	$	133,671	$	127,479	$	128,183		$	117,320

Net income (loss) attributable to SMLP	$	38,654	$	57,430	$	(49,971	)	$	(3,930	)
Less net income and IDRs attributable to General Partner		2,907		3,279		1,140			2,058
Less net income attributable to Series A Preferred Units		7,125		7,125		7,125			7,125
Net income (loss) attributable to common limited partners	$	28,622	$	47,026	$	(58,236	)	$	(13,113	)

Earnings (loss) per limited partner unit:
Common unit - basic	$	0.39	$	0.64	$	(0.79	)	$	(0.18	)
Common unit - diluted	$	0.39	$	0.64	$	(0.79	)	$	(0.18	)

DEFERRED REVENUE

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

DEFERRED REVENUE

9. DEFERRED REVENUE

Certain of our gathering and/or processing agreements provide for monthly or annual MVCs. The amount of the shortfall payment is based on the difference between the actual throughput volume shipped and/or processed for the applicable period and the MVC for the applicable period, multiplied by the applicable gathering or processing fee.

Many of our gas gathering agreements contain provisions that can reduce or delay the cash flows that we expect to receive from our MVCs to the extent that a customer's actual throughput volumes are above or below its MVC for the applicable contracted measurement period. These provisions include the following:

•

To the extent that a customer's throughput volumes are less than its MVC for the applicable period and the customer makes a shortfall payment, it may be entitled to an offset in one or more subsequent periods to the extent that its throughput volumes in subsequent periods exceed its MVC for those periods. In such a situation, we would not receive gathering fees on throughput in excess of that customer's MVC (depending on the terms of the specific gas gathering agreement) to the extent that the customer had made a shortfall payment with respect to one or more preceding measurement periods (as applicable).

•

To the extent that a customer's throughput volumes exceed its MVC in the applicable contracted measurement period, it may be entitled to apply the excess throughput against its aggregate MVC, thereby reducing the period for which its annual MVC applies. As a result of this mechanism, the weighted-average remaining period for which our MVCs apply will be less than the weighted-average of the original stated contract terms of our MVCs.

•

To the extent that certain of our customers' throughput volumes exceed its MVC for the applicable period, there is a crediting mechanism that allows the customer to build a bank of credits that it can utilize in the future to reduce shortfall payments owed in subsequent periods, subject to expiration if there is no shortfall in subsequent periods. The period over which this credit bank can be applied to future shortfall payments varies, depending on the particular gas gathering agreement.

A rollforward of current deferred revenue follows.

	Utica Shale		Williston Basin		DJ Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total current
	(In thousands)
Current deferred revenue, January 1, 2018	$	18	$	1,017	$	358	$	7,038	$	1,619	$	38	$	10,088
Additions		18		1,744		943		21,955		1,651		96		26,407
Less revenue recognized		18		1,347		562		21,377		1,628		96		25,028
Current deferred revenue, December 31, 2018		18		1,414		739		7,616		1,642		38		11,467
Additions		18		2,262		5,165		16,211		1,632		38		25,326
Less revenue recognized		18		1,743		3,044		16,813		1,644		38		23,300
Current deferred revenue, December 31, 2019	$	18	$	1,933	$	2,860	$	7,014	$	1,630	$	38	$	13,493

A rollforward of noncurrent deferred revenue follows.

	Utica Shale		Williston Basin		DJ Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total noncurrent
	(In thousands)
Noncurrent deferred, revenue, January 1, 2018	$	39	$	4,215	$	4,505	$	18,219	$	8,217	$	333	$	35,528
Additions		—		1,851		3,720		7,869		3,062		—		16,502
Less reclassification to current deferred revenue		18		1,673		941		8,146		1,651		97		12,526
Noncurrent deferred revenue, December 31, 2018		21		4,393		7,284		17,942		9,628		236		39,504
Additions		—		1,940		5,470		6,104		1,579		—		15,093
Less reclassification to current deferred revenue		18		2,699		5,165		6,336		1,632		38		15,888
Noncurrent deferred revenue, December 31, 2019	$	3	$	3,634	$	7,589	$	17,710	$	9,575	$	198	$	38,709

RELATED-PARTY TRANSACTIONS

12 Months Ended

Dec. 31, 2019

RELATED-PARTY TRANSACTIONS

15. RELATED-PARTY TRANSACTIONS

Acquisitions. See Notes 1 and 17.

Reimbursement of Expenses from General Partner. Our General Partner and its affiliates do not receive a management fee or other compensation in connection with the management of our business, but will be reimbursed for expenses incurred on our behalf. Under our Partnership Agreement, we reimburse our General Partner and its affiliates for certain expenses incurred on our behalf, including, without limitation, salary, bonus, incentive compensation and other amounts paid to our General Partner's employees and executive officers who perform services necessary to run our business. Our Partnership Agreement provides that our General Partner will determine in good faith the expenses that are allocable to us. The "Due to affiliate" line item on the consolidated balance sheet represents the payables to our General Partner for expenses incurred by it and paid on our behalf.

Expenses incurred by the General Partner and reimbursed by us under our Partnership Agreement were as follows:

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Operation and maintenance expense	$	28,643	$	29,061	$	27,450
General and administrative expense		32,222		30,119		30,899

In February 2017, SMP Holdings sold 4,000,000 common units representing limited partner interests in SMLP at a price to the public of $24.00 per common unit. Consistent with our obligations under the Partnership Agreement, we paid all costs and expenses of the secondary offering (other than underwriting discounts and fees and expenses of counsel and advisors to SMP Holdings in the sale). We did not receive any of the proceeds from the secondary offering.

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 443,528,000	$ 506,653,000	$ 488,741,000
Costs and expenses:
Cost of natural gas and NGLs	$ 63,438,000	$ 107,661,000	$ 57,237,000
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 97,587,000	$ 96,878,000	$ 93,882,000
General and administrative	54,139,000	52,877,000	54,681,000
Depreciation and amortization	110,206,000	107,100,000	115,475,000
Transaction costs	1,788,000	0	73,000
(Gain) loss on asset sales, net	(1,536,000)	0	527,000
Long-lived asset impairment	60,507,000	7,186,000	188,702,000
Goodwill impairment	16,211,000	0	0
Total costs and expenses	402,340,000	371,702,000	510,577,000
Other income (expense)	451,000	(169,000)	298,000
Interest expense	(74,429,000)	(60,535,000)	(68,131,000)
Early extinguishment of debt	0	0	(22,039,000)
Deferred Purchase Price Obligation	1,982,000	(20,975,000)	200,322,000
(Loss) income before income taxes and loss from equity method investees	(30,808,000)	53,272,000	88,614,000
Income tax expense	(1,174,000)	(33,000)	(341,000)
Loss from equity method investees	(337,851,000)	(10,888,000)	(2,223,000)
Net (loss) income	(369,833,000)	42,351,000	86,050,000
Net income attributable to noncontrolling interest	0	168,000	363,000
Net (loss) income attributable to SMLP	(369,833,000)	42,183,000	85,687,000
Net income attributable to General Partner, including IDRs	12,000	9,384,000	10,202,000
Net (loss) income attributable to limited partners	(369,845,000)	32,799,000	75,485,000
Series A Preferred Units
Costs and expenses:
Net (loss) income attributable to limited partners	28,500,000	28,500,000	3,563,000
Series A Preferred Units \| Subsidiary
Costs and expenses:
Net (loss) income attributable to limited partners	58,000	0	0
Common units
Costs and expenses:
Net (loss) income attributable to limited partners	$ (398,403,000)	$ 4,299,000	$ 71,922,000
(Loss) income per limited partner unit:
Basic (in dollars per share)	$ (4.84)	$ 0.06	$ 0.99
Diluted (in dollars per share)	$ (4.84)	$ 0.06	$ 0.98
Weighted-average limited partner units outstanding:
Basic (shares)	82,365	73,304	72,705
Diluted (shares)	82,365	73,615	73,047
Gathering Services and Related Fees
Revenues:
Total revenues	$ 326,747,000	$ 344,616,000	$ 394,427,000
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	86,994,000	134,834,000	68,459,000
Other Revenues
Revenues:
Total revenues	$ 29,787,000	$ 27,203,000	$ 25,855,000

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 317,503	$ 331,890	$ 329,527
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	29,292	30,285	34,011
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	39,126	39,969	41,246
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	69,437	76,701	66,413
Piceance Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	98,765	111,042	111,113
DJ Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	18,668	7,558	6,624
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	43,043	43,268	46,232
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	20,051	24,267	23,888
Permian Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (879)	$ (1,200)	$ 0

EQUITY METHOD INVESTMENTS - Statements of Operations Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2017
OGC
Schedule Of Equity Method Investments [Line Items]
Total revenues	$ 142,138	$ 142,398	$ 140,679
Total operating expenses	108,234	136,722	111,897
Net income (loss)	33,897	5,670	28,785
OCC
Schedule Of Equity Method Investments [Line Items]
Total revenues	8,601	10,177	8,607
Total operating expenses	38,815	9,053	8,298
Net income (loss)	$ (30,214)	$ 498	$ (907)

GOODWILL - Schedule of goodwill (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Accumulated goodwill impairment	$ 319,261	$ 303,050	$ 303,050
Piceance Basin
Goodwill [Line Items]
Accumulated goodwill impairment	45,478	45,478	45,478
Williston Basin
Goodwill [Line Items]
Accumulated goodwill impairment	257,572	$ 257,572	$ 257,572
Marcellus Shale
Goodwill [Line Items]
Accumulated goodwill impairment	$ 16,211

PARTNERS' CAPITAL AND MEZZANINE CAPITAL

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

PARTNERS' CAPITAL AND MEZZANINE CAPITAL

12. PARTNERS' CAPITAL AND MEZZANINE CAPITAL

A rollforward of the number of common limited partner, preferred limited partner and General Partner units follows.

	Limited partners
	Series A Preferred Units		Common		General Partner
Units, January 1, 2017		—		72,111,121		1,471,187
Units issued in connection with the November 2017 Equity Offering		300,000		—		—
Net units issued under the SMLP LTIP		—		211,327		—
Units issued under ATM program		—		763,548		—
General Partner 2% contribution		—		—		19,812
Units, December 31, 2017		300,000		73,085,996		1,490,999
Net units issued under the SMLP LTIP		—		304,857		—
Units, December 31, 2018		300,000		73,390,853		1,490,999
Conversion of General Partner economic interests		—		8,750,000		(1,490,999	)
Net units issued under the SMLP LTIP		—		638,335		—
DPPO partial settlement		—		10,714,285		—
Units, December 31, 2019		300,000		93,493,473		—

GP/IDR Exchange. On March 22, 2019, we cancelled our IDRs and converted our 2% economic GP interest to a non-economic GP interest in exchange for 8,750,000 SMLP common units which were issued to SMP Holdings in the Equity Restructuring. These units had a fair value of $84.5 million as of the transaction date (March 22, 2019). As a result of the Equity Restructuring, the general partner units and IDRs were eliminated, are no longer outstanding, and no longer participate in distributions of cash from SMLP. Energy Capital Partners continues to control the non-economic GP interest in SMLP.

Immediately following the Equity Restructuring, SMP Holdings directly owned a 41.8% limited partner interest in SMLP and an affiliate of Energy Capital Partners II, LLC directly owned a 7.2% limited partner interest in SMLP.

Our General Partner held IDRs (through the Equity Restructuring). Our payment of IDRs as reported in distributions to unitholders – General Partner in the statements of partners' capital during the years ended December 31 follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
IDR payments	$	2,139	$	8,535	$	8,460

For the purposes of calculating net income attributable to General Partner in the statements of operations and partners' capital, the financial impact of IDRs was recognized in respect of the quarter for which the distributions were declared. For the purposes of calculating distributions to unitholders in the statements of partners' capital and cash flows, IDR payments are recognized in the quarter in which they are paid.

Unit Offerings. In February 2017, we completed a secondary underwritten public offering of 4,000,000 SMLP common units held by a subsidiary of Summit Investments pursuant to the 2016 SRS. We did not receive any proceeds from this offering.

At-the-market Program. In February 2017, we executed a new equity distribution agreement and filed a prospectus with the SEC for the issuance and sale from time to time of SMLP common units having an aggregate offering price of up to $150.0 million (the "ATM Program"). During the years ended December 31, 2019 and 2018, there were no transactions under the ATM Program. During the year ended December 31, 2017, we sold 763,548 units under the ATM Program for aggregate gross proceeds of $17.7 million, and paid approximately $0.2 million as compensation to the sales agents pursuant to the terms of the equity distribution agreement.

Series A Preferred Units. In November 2017, we issued 300,000 Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units (the “Series A Preferred Units”) representing limited partner interests in the Partnership at a price to the public of $1,000 per unit. We used the net proceeds of $293.2 million (after deducting underwriting discounts and offering expenses) to repay outstanding borrowings under our Revolving Credit Facility.

The Series A Preferred Units rank senior to (i) common units representing limited partner interests in the Partnership and (ii) each other class or series of limited partner interests or other equity securities in the Partnership that may be established in the future that expressly ranks junior to the Series A Preferred Units as to the payment of distributions and amounts payable upon a liquidation event (the “Junior Securities”). The Series A Preferred Units rank equal in all respects with each class or series of limited partner interests or other equity securities in the Partnership that may be established in the future that is not expressly made senior or subordinated to the Series A Preferred Units as to the payment of distributions and amounts payable on a liquidation event (the “Parity Securities”). The Series A Preferred Units rank junior to (i) all of the Partnership’s existing and future indebtedness and other liabilities with respect to assets available to satisfy claims against the Partnership and (ii) each other class or series of limited partner interests or other equity securities in the Partnership established in the future that is expressly made senior to the Series A Preferred Units as to the payment of distributions and amounts payable upon a liquidation event. Income is allocated to the Series A Preferred Units in an amount equal to the earned distributions for the respective reporting period.

Distributions on the Series A Preferred Units are cumulative and compounding and are payable semi-annually in arrears on the 15th day of each June and December through and including December 15, 2022, and, thereafter, quarterly in arrears on the 15th day of March, June, September and December of each year (each, a “Distribution Payment Date”) to holders of record as of the close of business on the first business day of the month of the applicable Distribution Payment Date, in each case, when, as, and if declared by the General Partner out of legally available funds for such purpose.

The initial distribution rate for the Series A Preferred Units is 9.50% per annum of the $1,000 liquidation preference per Series A Preferred Unit. On and after December 15, 2022, distributions on the Series A Preferred Units will accumulate for each distribution period at a percentage of the liquidation preference equal to the three-month LIBOR plus a spread of 7.43%.

Subsidiary Series A Preferred Units. In December 2019, we issued 30,000 Subsidiary Series A Preferred Units representing limited partner interests in Permian Holdco at a price of $1,000 per unit. We used the net proceeds of $27.4 million (after deducting underwriting discounts and offering expenses) to fund capital expenses associated with the Double E Project.

On January 16, 2020, we issued 10,000 Subsidiary Series A Preferred Units representing limited partner interests in Permian Holdco at a price of $1,000 per unit. We used the net proceeds of $9.7 million (after deducting underwriting discounts and offering expenses) to fund capital expenses associated with the Double E Project.

The proceeds associated with the issuance of Subsidiary Series A Preferred Units is classified as restricted cash on the accompanying consolidated balance sheets in accordance with the underlying agreement with TPG Energy Solutions Anthem, L.P. until the related funding is used for the Double E Project.

Accounting for the Subsidiary Series A Preferred Units

These preferred units are considered redeemable securities under GAAP due to the existence of certain redemption provisions that are outside of our control. Therefore, the securities are classified as temporary equity in the mezzanine section of the consolidated balance sheet.

Initial and Subsequent Measurement

We initially recognized these preferred units at the time of issuance in the amount of $27.4 million, their issuance date fair value, net of issuance costs. We will not be required to adjust the carrying amount of these preferred units unless it becomes probable that the units would become redeemable. If events or circumstances indicate that redemption is probable, we would accrete these preferred units to the redemption value over a period of time comprising the date redemption first became probable and the date the units can first be redeemed.

The Subsidiary Series A Preferred Units rank senior to each other class or series of limited partner interests or other equity securities in Permian Holdco that may be established in the future that expressly ranks junior to the Subsidiary Series A Preferred Units as to the payment of distributions and amounts payable upon a liquidation event (the “Junior Securities”). The Subsidiary Series A Preferred Units rank equal in all respects with each class or series of limited partner interests or other equity securities in Permian Holdco that may be established in the future that is not expressly made senior or subordinated to the Subsidiary Series A Preferred Units as to the payment of distributions and amounts payable on a liquidation event (the “Parity Securities”). The Subsidiary Series A Preferred Units rank junior to (i) all of Permian Holdco’s or a subsidiary of Permian Holdco’s future indebtedness and other liabilities with respect to assets available to satisfy claims against Permian Holdco and (ii) each other class or series of limited partner interests or other equity securities in Permian Holdco established in the future that is expressly made senior to the Subsidiary Series A Preferred Units as to the payment of distributions and amounts payable upon a liquidation event. Income is allocated to the Subsidiary Series A Preferred Units in an amount equal to the earned distributions for the respective reporting period.

Distributions on the Subsidiary Series A Preferred Units are cumulative and compounding and are payable 21 days following the quarterly period ended March, June, September and December of each year (each, a “Series A Distribution Payment Date”) to holders of record as of the close of business on the first business day of the month of the applicable Series A Distribution Payment Date, in each case, when, as, and if declared by Permian Holdco out of legally available funds for such purpose.

The distribution rate for the Subsidiary Series A Preferred Units is 7.00% per annum of the $1,000 liquidation preference per Subsidiary Series A Preferred Unit. A pro-rated initial distribution on the Subsidiary Series A Preferred Units was Paid-in-kind (“PIK”) on January 21, 2020 in an amount equal to 7.00% per Subsidiary Series A Preferred Unit plus 1.00% per annum of the undrawn commitment units.

Noncontrolling Interest. At December 31, 2017, we recorded Summit Investments' indirect retained ownership interest in OpCo and its subsidiaries as a noncontrolling interest in the consolidated financial statements. In November 2018, a subsidiary of SMLP purchased the remaining 1% ownership interest in OpCo held by a subsidiary of Summit Investments for approximately $10.9 million. As a result of this transaction, other than our investment in Ohio Gathering, our investment in Double E and the Subsidiary Series A Preferred Units at Permian Holdco, our business activities are conducted through wholly owned operating subsidiaries.

Cash Distribution Policy

Our Partnership Agreement requires that we distribute all of our available cash, subject to reserves established by our General Partner, within 45 days after the end of each quarter to unitholders of record on the applicable record date. The amount of distributions paid under our policy is subject to fluctuations based on the amount of cash we generate from our business and the decision to make any distribution is determined by our General Partner, taking into consideration the terms of our Partnership Agreement.

General Partner Interest. On March 22, 2019, we cancelled our IDRs and converted our 2% economic GP interest to a non-economic GP interest in exchange for 8,750,000 SMLP common units which were issued to SMP Holdings in the Equity Restructuring.

Cash Distributions Paid and Declared. We paid the following per-unit distributions during the years ended December 31:

	Year ended December 31,
	2019		2018		2017
Per-unit distributions to unitholders	$	1.4375	$	2.300	$	2.300

On January 29, 2020, the Board of Directors declared a distribution of $0.125 per unit for the quarterly period ended December 31, 2019. This distribution, which totaled $11.7 million, was paid on February 14, 2020 to unitholders of record at the close of business on February 7, 2020.

With respect to our Subsidiary Series A Preferred Units relating to the fourth quarter of 2019, we declared a payment-in-kind ("PIK") of the quarterly distribution, which resulted in the pro-rated issuance of 47 Subsidiary Series A Preferred Units. This PIK amount equates to a pro-rated distribution of $1.5556 per Subsidiary Series A Preferred Unit for the fourth quarter in 2019, or $70 on a full year annualized basis.

SEGMENT INFORMATION - Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	$ 3,476	$ (3,632)	$ (41,373)
Net change in deferred revenue for MVC shortfall payments			(40,758)
Expected MVC shortfall adjustments			(615)
Total adjustments related to MVC shortfall payments	3,476	(3,632)	(41,373)
Williston Basin
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	0	0	(37,693)
Net change in deferred revenue for MVC shortfall payments			(37,693)
Expected MVC shortfall adjustments			0
Total adjustments related to MVC shortfall payments	0	0	(37,693)
Piceance Basin
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	(103)	10	(3,068)
Net change in deferred revenue for MVC shortfall payments			(3,065)
Expected MVC shortfall adjustments			(3)
Total adjustments related to MVC shortfall payments	(103)	10	(3,068)
Barnett Shale
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	3,579	(3,642)	(612)
Net change in deferred revenue for MVC shortfall payments			0
Expected MVC shortfall adjustments			(612)
Total adjustments related to MVC shortfall payments	$ 3,579	$ (3,642)	$ (612)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Cash, Cash Equivalents and Restricted Cash

Cash, Cash Equivalents and Restricted Cash. We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. Cash that is held by a major bank and has restrictions on its availability to us is classified as restricted cash. See Note 12 for additional information.

Accounts Receivable

Accounts Receivable. Accounts receivable relate to gathering and other services provided to our customers and other counterparties. We evaluate the collectability of accounts receivable and the need for an allowance for doubtful accounts based on customer-specific facts and circumstances. To the extent we doubt the collectability of a specific customer or counterparty receivable, we recognize an allowance for doubtful accounts. Uncollectible receivables are written off when a settlement is reached for an amount that is less than the outstanding historical balance or a receivable amount is deemed otherwise unrealizable.

Property, Plant and Equipment

Property, Plant and Equipment. We record property, plant and equipment at historical cost of construction or fair value of the assets at acquisition. We capitalize expenditures that extend the useful life of an asset or enhance its productivity or efficiency from its original design over the expected remaining period of use. For maintenance and repairs that do not add capacity or extend the useful life of an asset, we recognize expenditures as an expense as incurred. We capitalize project costs incurred during construction, including interest on funds borrowed to finance the construction of facilities, as construction in progress.

We record depreciation on a straight-line basis over an asset’s estimated useful life. We base our estimates for useful life on various factors including age (in the case of acquired assets), manufacturing specifications, technological advances and historical data concerning useful lives of similar assets. Estimates of useful lives follow.

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

Construction in progress is depreciated consistent with its applicable asset class once it is placed in service. Land and line fill are not depreciated.

We base an asset’s carrying value on estimates, assumptions and judgments for useful life and salvage value. Upon sale, retirement or other disposal, we remove the carrying value of an asset and its accumulated depreciation from our balance sheet and recognize the related gain or loss, if any.

Accrued capital expenditures are reflected in trade accounts payable.

Asset Retirement Obligations

Asset Retirement Obligations. We record a liability for asset retirement obligations only if and when a future asset retirement obligation with a determinable life is identified. For identified asset retirement obligations, we then evaluate whether the expected date and related costs of retirement can be estimated. We have concluded that our gathering and processing assets have an indeterminate life because they are owned and will operate for an indeterminate period when properly maintained. Because we did not have sufficient information to reasonably estimate the amount or timing of such obligations and we have no current plan to discontinue use of any significant assets, we did not provide for any asset retirement obligations as of December 31, 2019 or 2018.

Amortizing Intangibles

Amortizing Intangibles. Upon the acquisition of DFW Midstream, certain of its gas gathering contracts were deemed to have above-market pricing structures. We have recognized the above-market contracts as favorable gas gathering contracts. We amortize the favorable contracts using a straight-line method over the contract’s estimated useful life. We define useful life as the period over which the contract is expected to contribute to our future cash flows. These contracts have original terms ranging from 10 years to 20 years. We recognize the amortization expense associated with these contracts in Other revenues.

We amortize all other gas gathering contracts, or contract intangibles, over the period of economic benefit based upon expected revenues over the life of the contract. The useful life of these contracts ranges from 3 years to 25 years. We recognize the amortization expense associated with these contracts in Depreciation and amortization expense.

We have rights-of-way associated with city easements and easements granted within existing rights-of-way. We amortize these intangible assets over the shorter of the contractual term of the rights-of-way or the estimated useful life of the gathering system. The contractual terms of the rights-of-way range from 20 years to 30 years. We recognize the amortization expense associated with rights-of-way assets in Depreciation and amortization expense.

Goodwill

Goodwill. Goodwill represents consideration paid in excess of the fair value of the net identifiable assets acquired in a business combination. We evaluate goodwill for impairment annually on September 30. In September 2019, in connection with our annual impairment evaluation, we determined that the fair value of the Mountaineer Midstream reporting unit did not exceed its carrying value and we recognized a goodwill impairment charge of $16.2 million. As of December 31, 2019, we did not have a goodwill balance on our consolidated balance sheet.

Equity Method Investments

Equity Method Investments. We account for investments in which we exercise significant influence using the equity method so long as we (i) do not control the investee and (ii) are not the primary beneficiary. We recognize these investments in investment in equity method investees in the accompanying consolidated balance sheets. We recognized (i) our proportionate share of earnings or loss in net income for Ohio Gathering, on a one-month lag, and (ii) an other-than-temporary impairment for Ohio Gathering, based on the financial information available to us during the reporting period.

We recognize an other-than-temporary impairment for losses in the value of equity method investees when evidence indicates that the carrying amount is no longer supportable. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the equity method investee to sustain an earnings capacity that would justify the carrying amount of the investment. A current fair value of an investment that is less than its carrying amount may indicate a loss in value of the investment. We evaluate our equity method investments whenever a triggering event exists that would indicate a need to assess the investment for potential impairment.

Other Noncurrent Assets

Other Noncurrent Assets. Other noncurrent assets primarily consist of external costs incurred in connection with the closing of our Revolving Credit Facility and related amendments. We capitalize and then amortize these debt issuance costs on a straight-line basis, which approximates the effect of the effective interest rate method, over the life of the respective debt instrument. We recognize the amortization of the Revolving Credit Facility debt issuance costs in interest expense.

Debt Issuance Costs

Debt Issuance Costs. Debt issuance costs, other than those associated with our Revolving Credit Facility, are reflected in the carrying value of the Senior Notes as an adjustment to the principal amount and amortized on a straight-line basis, which approximates the effect of the effective interest rate method, over the life of the respective debt instrument. We recognize the amortization of the Senior Notes debt issuance costs in interest expense.

Deferred Purchase Price Obligation

Deferred Purchase Price Obligation. We recognize a liability for the Deferred Purchase Price Obligation to reflect the present value of the estimated Remaining Consideration for the acquisition of the 2016 Drop Down Assets. In March 2016, we recognized the Deferred Purchase Price Obligation in connection with the 2016 Drop Down. On November 7, 2019, we and SMP Holdings entered into a second amendment (the “Second Amendment”) to the Contribution Agreement between us and SMP Holdings dated February 25, 2016, as amended. On November 15, 2019, we made a cash payment of $51.75 million and issued 10,714,285 common units to SMP Holdings (the “November 2019 Prepayment”). In addition, the parties reduced the Remaining Consideration due to SMP Holdings by $19.25 million. Following the November 2019 Prepayment, the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest will accrue (and will be payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020 (see Note 17 for additional information).

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets. We test assets for impairment when events or circumstances indicate that the carrying value of a long-lived asset may not be recoverable. The carrying value of a long-lived asset (except goodwill) is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from its use and eventual disposition. If we conclude that an asset's carrying value will not be recovered through future cash flows, we recognize an impairment loss on the long-lived asset equal to the amount by which the carrying value exceeds its fair value. We determine fair value using either a market-based approach, an income-based approach or a combination of the two approaches.

Derivative Contracts

Derivative Contracts. We have commodity price exposure related to our sale of the physical natural gas we retain from certain DFW Midstream customers and our procurement of electricity to operate the DFW Midstream system's electric-drive compression assets. Our gas gathering agreements with certain DFW Midstream customers permit us to retain a certain quantity of natural gas that we gather to offset the power costs we incur to operate these electric-drive compression assets. We manage this direct exposure to natural gas and power prices through the use of forward power purchase contracts with wholesale power providers that require us to purchase a fixed quantity of power at a fixed heat rate based on prevailing natural gas prices based on the Henry Hub Index. We sell retainage natural gas at prices that are based on the Atmos Zone 3 Index. By basing the power prices on a system and basin-relevant market, we are able to closely associate the relationship between the compression electricity expense and natural gas retainage sales.

Restructuring Cost

Restructuring Costs. Our restructuring costs are comprised primarily of employee termination costs related to headcount reductions. A liability for costs associated with an exit or disposal activity is recognized and measured initially at fair value only when the liability is incurred. Our restructuring charges also include relocation expenses and advisory costs. We reassess the liability periodically based on market conditions. Refer to Note 17 for additional details.

Fair Value of Financial Instruments

Fair Value of Financial Instruments. The fair-value-measurement standard under GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which the inputs are observable. The three levels of the fair value hierarchy are as follows:

•

Level 1. Inputs represent quoted prices in active markets for identical assets or liabilities;

•

Level 2. Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs); and

•

Level 3. Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an internally developed present value of future cash flows model that underlies management's fair value measurement).

Commitments and Contingencies

Commitments and Contingencies. We record accruals for loss contingencies when we determine that it is probable that a liability has been incurred and that such economic loss can be reasonably estimated. Such determinations are subject to interpretations of current facts and circumstances, forecasts of future events and estimates of the financial impacts of such events. We recognize gain contingencies when their realization is assured beyond a reasonable doubt.

Noncontrolling Interest

Noncontrolling Interest. Noncontrolling interest represented the ownership interests of third-party entities in the net assets of our consolidated subsidiaries.

Revenue Recognition

Revenue Recognition. The majority of our revenue is derived from long-term, fee-based contracts with original terms of up to 25 years. We account for revenue in accordance with Topic 606, which we adopted on January 1, 2018, using the modified retrospective method. See below for further discussion of the adoption.

We recognize revenue earned from fee-based gathering, compression, treating and processing services in gathering services and related fees. We also earn revenue in the Williston Basin and Permian Basin reporting segments from the sale of physical natural gas purchased from our customers under certain percent-of-proceeds arrangements. Under ASC Topic 606, these gathering contracts are presented net within cost of natural gas and NGLs. We sell natural gas that we retain from certain customers in the Barnett Shale reporting segment to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate and NGLs retained from certain of our gathering services in the Piceance Basin and Permian Basin reporting segments. Revenues from the sale of natural gas and condensate are recognized in natural gas, NGLs and condensate sales; the associated expense is included in operation and maintenance expense. Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis, with the revenue component recognized in Other revenues.

We provide gathering and/or processing services principally under contracts that contain one or more of the following arrangements:

•

Fee-based arrangements. Under fee-based arrangements, we receive a fee or fees for one or more of the following services (i) natural gas gathering, treating, compressing and/or processing and (ii) crude oil and/or produced water gathering.

•

Percent-of-proceeds arrangements. Under percent-of-proceeds arrangements, we generally purchase natural gas from producers at the wellhead, or other receipt points, gather the wellhead natural gas through our gathering system, treat the natural gas, process the natural gas and/or sell the natural gas to a third party for processing. We then remit to our producers an agreed-upon percentage of the actual proceeds received from sales of the residue natural gas and NGLs. Certain of these arrangements may also result in returning all or a portion of the residue natural gas and/or the NGLs to the producer, in lieu of returning sales proceeds. The margins earned are directly related to the volume of natural gas that flows through the system and the price at which we are able to sell the residue natural gas and NGLs.

Certain of our gathering and/or processing agreements provide for monthly or annual MVCs. Under these MVCs, our customers agree to ship and/or process a minimum volume of production on our gathering systems or to pay a minimum monetary amount over certain periods during the term of the MVC. A customer must make a shortfall payment to us at the end of the contracted measurement period if its actual throughput volumes are less than its contractual MVC for that period. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent contracted measurement periods to the extent that such customer's throughput volumes in a subsequent contracted measurement period exceed its MVC for that contracted measurement period.

We recognize customer obligations under their MVCs as revenue and contract assets when (i) we consider it remote that the customer will utilize shortfall payments to offset gathering or processing fees in excess of its MVCs in subsequent periods; (ii) the customer incurs a shortfall in a contract with no banking mechanism or claw back provision; (iii) the customer’s banking mechanism has expired; or (iv) it is remote that the customer will use its unexercised right. In making this determination, we consider both quantitative and qualitative facts and circumstances, including, but not limited to, contract terms, capacity of the associated pipeline or receipt point and/or expectations regarding future investment, drilling and production.

Unit-Based Compensation

Unit-Based Compensation. For awards of unit-based compensation, we determine a grant date fair value and recognize the related compensation expense in the statements of operations over the vesting period of the respective awards.

Income Taxes

Income Taxes. As a partnership, we are generally not subject to federal and state income taxes, except as noted below. However, our unitholders are individually responsible for paying federal and state income taxes on their share of our taxable income. Net income or loss for GAAP purposes may differ significantly from taxable income reportable to our unitholders as a result of differences between the tax basis and the GAAP basis of assets and liabilities and the taxable income allocation requirements under our Partnership Agreement. The aggregate difference in the basis of the Partnership’s net assets for financial and income tax purposes cannot be readily determined as the Partnership does not have access to the information about each partner’s tax attributes related to the Partnership.

In general, legal entities that are chartered, organized or conducting business in the state of Texas are subject to a franchise tax (the "Texas Margin Tax"). The Texas Margin Tax has the characteristics of an income tax because it is determined by applying a tax rate to a tax base that considers both revenues and expenses. Our financial statements reflect provisions for these tax obligations.

Earnings or Loss Per Unit

Earnings or Loss Per Unit. We determine basic EPU by dividing the net income or loss that is attributed, in accordance with the net income and loss allocation provisions of our Partnership Agreement, to common limited partners under the two-class method, after deducting (i) any payment of IDRs, by the weighted-average number of limited partner units outstanding (for periods presented through the Equity Restructuring), (ii) the General Partner's approximate 2% interest in net income or loss (for periods presented up through the Equity Restructuring), and (iii) net income attributable to Series A Preferred Units and Subsidiary Series A Preferred Units. Diluted EPU reflects the potential dilution that could occur if securities or other agreements to issue common units, such as unit-based compensation, were exercised, settled or converted into common units and included in the weighted-average number of units outstanding. When it is determined that potential common units resulting from an award subject to performance or market conditions should be included in the diluted EPU calculation, the impact is reflected by applying the treasury stock method.

Environmental Matters

Environmental Matters. We are subject to various federal, state and local laws and regulations relating to the protection of the environment. Liabilities for loss contingencies, including environmental remediation costs, arising from claims, assessments, litigation, fines and penalties and other sources are charged to expense when it is probable that a liability has been incurred and the amount of the assessment and/or remediation can be reasonably estimated. We accrue for losses associated with environmental remediation obligations when such losses are probable and reasonably estimable. Such accruals are adjusted as further information develops or circumstances change. Recoveries of environmental remediation costs from other parties or insurers are recorded as assets when their realization is assured beyond a reasonable doubt.

Recent Accounting Pronouncements

Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. We review new pronouncements to determine the impact, if any, on our financial statements. Accounting standards that have or could possibly have a material effect on our financial statements are discussed below.

Recently Adopted Accounting Pronouncements. We have recently adopted the following accounting pronouncement:

•

ASU No. 2016-02 Leases (“Topic 842"). We adopted Topic 842 with a date of initial application of January 1, 2019. We applied Topic 842 by recognizing (i) a $5.4 million right-of-use (“ROU”) asset which represents the right to use, or to control the use of, specified assets for a lease term. The ROU asset is included in the Property, plant and equipment, net caption on the consolidated balance sheet; and (ii) a $5.4 million lease liability for the obligation to make lease payments arising from the leases. The lease liability is included in the Other current liabilities and Other noncurrent liabilities captions on the consolidated balance sheet. The comparative information has not been adjusted and is reported under the accounting standards in effect for those periods. Refer to Note 16 for additional information.

Accounting Pronouncements Pending Adoption. We have not yet adopted the following accounting pronouncements as of December 31, 2019:

•

ASU No. 2018-13 Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 updates the disclosure requirements on fair value measurements including new disclosures for the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 modifies existing disclosures including clarifying the measurement uncertainty disclosure. ASU 2018-13 removes certain existing disclosure requirements including the amount and reasons for transfers between Level 1 and Level 2 fair value measurements and the policy for the timing of transfer between levels. The adoption of ASU 2018-13 on January 1, 2020 did not have a material impact on our consolidated financial statement disclosures.

•

ASU No. 2016-13 Financial Instruments – Credit Losses (“ASU 2016-13”). ASU 2016-13 requires the use of a current expected loss model for financial assets measured at amortized cost and certain off-balance sheet credit exposures. Under this model, entities will be required to estimate the lifetime expected credit losses on such instruments based on historical experience, current conditions, and reasonable and supportable forecasts. This amended guidance also expands the disclosure requirements to enable users of financial statements to understand an entity’s assumptions, models and methods for estimating expected credit losses. The changes are effective for annual and interim periods beginning after December 15, 2019, and amendments should be applied using a modified retrospective approach. The adoption of ASU 2016-13 on January 1, 2020 did not have a material impact on our consolidated financial statements or disclosures.

Basis of Presentation

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

Construction in progress is depreciated consistent with its applicable asset class once it is placed in service. Land and line fill are not depreciated.

Accrued capital expenditures are reflected in trade accounts payable.

Accounting standards related to derivative instruments and hedging activities allow for normal purchase or sale elections and hedge accounting designations, which generally eliminate or defer the requirement for mark-to-market recognition in net income and thus reduce the volatility of net income that can result from fluctuations in fair values. We have designated these contracts as normal under the normal purchase and sale exception under the accounting standards for derivatives. We do not enter into risk management contracts for speculative purposes.

•

Level 1. Inputs represent quoted prices in active markets for identical assets or liabilities;

•

Noncontrolling Interest. Noncontrolling interest represented the ownership interests of third-party entities in the net assets of our consolidated subsidiaries.

We provide gathering and/or processing services principally under contracts that contain one or more of the following arrangements:

•

Recently Adopted Accounting Pronouncements. We have recently adopted the following accounting pronouncement:

•

Accounting Pronouncements Pending Adoption. We have not yet adopted the following accounting pronouncements as of December 31, 2019:

•

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING - 2016 Drop Down (Details) - Drop Down Assets 2016 Acquisition - USD ($) $ in Thousands				1 Months Ended		10 Months Ended	12 Months Ended
	Mar. 31, 2020	Nov. 15, 2019	Nov. 07, 2019	Mar. 31, 2019	Jun. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016	Jun. 30, 2020
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 51,750	$ 51,750
Working capital adjustment					$ 600
Remaining cash consideration payable			$ 180,750			$ 303,500
Remaining consideration description			the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020	Remaining Consideration at $303.5 million, with such amount to be paid by the Partnership in one or more payments over the period from March 1, 2020 through December 31, 2020, in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, at the discretion of the Partnership. At least 50% of the Remaining Consideration must be paid on or before June 30, 2020 and interest will accrue at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020			the Remaining Consideration is $180.75 million. The parties also extended the final date by which we are obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) our common units or (iii) a combination of cash and our common units, and interest will accrue (and will be payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020
Business acquisition, reduced amount of consideration			$ 19,250
Estimated future payment obligation							$ 178,500
Deferred purchase price obligation							$ 180,750
Discount rate							5.25%
Common units
Business Acquisition [Line Items]
Business acquisition, share issued (shares)		10,714,285	10,714,285
Scenario Forecast
Business Acquisition [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%					8.00%
Scenario Forecast \| Minimum
Business Acquisition [Line Items]
Minimum remaining consideration to be paid percentage									50.00%
Revolving credit facility
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross								$ 360,000

SEGMENT INFORMATION

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

SEGMENT INFORMATION

4. SEGMENT INFORMATION

As of December 31, 2019, our reportable segments are:

•

the Utica Shale, which is served by Summit Utica;

•

Ohio Gathering, which includes our ownership interest in OGC and OCC;

•

the Williston Basin, which is served by Polar and Divide and Bison Midstream;

•

the DJ Basin, which is served by Niobrara G&P;

•

the Permian Basin, which is served by Summit Permian;

•

the Piceance Basin, which is served by Grand River;

•

the Barnett Shale, which is served by DFW Midstream; and

•

the Marcellus Shale, which is served by Mountaineer Midstream.

Until March 22, 2019, we owned Tioga Midstream, a crude oil, produced water and associated natural gas gathering system operating in the Williston Basin. Until December 1, 2019, we owned certain assets in the Red Rock Gathering system operating in the Piceance Basin. Refer to Note 17 to the consolidated financial statements for details on the sale of Tioga Midstream and on the sale of certain assets in the Red Rock Gathering system.

Each of our reportable segments provides midstream services in a specific geographic area. Our reportable segments reflect the way in which we internally report the financial information used to make decisions and allocate resources in connection with our operations.

The Ohio Gathering reportable segment includes our investment in Ohio Gathering. Income or loss from equity method investees, as reflected on the statements of operations, relates to Ohio Gathering and is recognized and disclosed on a one-month lag (see Note 8).

For the year ended December 31, 2019, other than the investment activity described in Note 8, Double E did not have any results of operations given that the Double E Project is currently under development. The Double E Project is expected to be operational in the third quarter of 2021.

Corporate and Other represents those results that are: (i) not specifically attributable to a reportable segment; (ii) not individually reportable (such as Double E); or (iii) that have not been allocated to our reportable segments for the purpose of evaluating their performance, including certain general and administrative expense items, certain natural gas and crude oil marketing services and transaction costs.

Assets by reportable segment follow.

	December 31,
	2019		2018			2017
	(In thousands)
Assets (1):
Utica Shale	$	206,368	$	207,357		$	212,311
Ohio Gathering		275,000		649,250			690,485
Williston Basin		452,152		526,819			512,860
DJ Basin		205,308		166,580			79,438
Permian Basin		185,708		145,702			57,590
Piceance Basin		631,140		699,638			719,284
Barnett Shale		350,638		376,564			383,306
Marcellus Shale		184,631		208,790			217,362
Total reportable segment assets		2,490,945		2,980,700			2,872,636
Corporate and Other		82,506		44,181			22,406
Eliminations		—		(4,319	)		(249	)
Total assets	$	2,573,451	$	3,020,562		$	2,894,793

Revenues by reportable segment follow.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Revenues (1):
Utica Shale	$	33,991		$	35,233		$	38,907
Williston Basin		105,651			123,650			161,503
DJ Basin		26,050			15,294			11,860
Permian Basin		20,303			958			—
Piceance Basin		133,638			155,519			154,893
Barnett Shale		71,802			68,265			71,667
Marcellus Shale		24,471			29,573			30,394
Total reportable segments revenue		415,906			428,492			469,224
Corporate and Other		30,552			88,286			26,446
Eliminations		(2,930	)		(10,125	)		(6,929	)
Total revenues	$	443,528		$	506,653		$	488,741

(1) Excludes revenues earned by Ohio Gathering due to equity method accounting.

Counterparties accounting for more than 10% of total revenues were as follows:

	Year ended December 31,
	2019			2018			2017
Percentage of total revenues (1):
Counterparty A - Piceance Basin		11	%	*			*
Counterparty B - Williston Basin		10	%	*				13	%
Counterparty C - Piceance Shale	*				10	%	*
Counterparty D - Barnett Shale	*			*			*

(1) Excludes revenues earned by Ohio Gathering due to equity method accounting.

* Less than 10%

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	7,659	$	7,672	$	7,009
Williston Basin		19,829		22,642		33,772
DJ Basin		3,732		3,133		2,636
Permian Basin		4,868		243		—
Piceance Basin		47,018		46,919		46,289
Barnett Shale (2)		16,575		15,325		15,001
Marcellus Shale		9,141		9,090		9,047
Total reportable segment depreciation and amortization		108,822		105,024		113,754
Corporate and Other		2,604		1,743		1,118
Total depreciation and amortization	$	111,426	$	106,767	$	114,872

(1) Excludes depreciation and amortization recognized by Ohio Gathering due to equity method accounting.

(2) Includes the amortization expense associated with our favorable and unfavorable (for 2018) gas gathering contracts as reported in Other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	3,902	$	5,719	$	22,921
Williston Basin		30,861		25,202		17,309
DJ Basin		80,487		64,920		7,150
Permian Basin		44,955		83,823		56,020
Piceance Basin		1,946		7,887		16,564
Barnett Shale (2)		184		1,370		569
Marcellus Shale		693		1,030		641
Total reportable segment capital expenditures		163,028		189,951		121,174
Corporate and Other		19,263		10,635		3,041
Total cash paid for capital expenditures	$	182,291	$	200,586	$	124,215

(1)	Excludes cash paid for capital expenditures by Ohio Gathering due to equity method accounting.

(2)	For the year ended December 31, 2019, the amount includes sales tax reimbursements of $1.1 million.

For the years ended December 31, 2019 and 2018, Corporate and Other includes cash paid of $1.6 million and $3.3 million, respectively, for corporate purposes; the remainder represents capital expenditures relating to the Double E Project.

We assess the performance of our reportable segments based on segment adjusted EBITDA. We define segment adjusted EBITDA as total revenues less total costs and expenses; plus (i) other income excluding interest income, (ii) our proportional adjusted EBITDA for equity method investees, (iii) depreciation and amortization, (iv) adjustments related to MVC shortfall payments, (v) adjustments related to capital reimbursement activity, (vi) unit-based and noncash compensation, (vii) change in the Deferred Purchase Price Obligation fair value, (viii) impairments (ix) other noncash expenses or losses, less other noncash income or gains and (x) restructuring expenses. We define proportional adjusted EBITDA for our equity method investees as the product of (i) total revenues less total expenses, excluding impairments and other noncash income or expense items, and amortization for deferred contract costs; and (ii) our ownership interest in Ohio Gathering during the respective period.

For the purpose of evaluating segment performance, we exclude the effect of Corporate and Other revenues and expenses, such as certain general and administrative expenses (including compensation-related expenses and professional services fees), certain natural gas and crude oil marketing services, transaction costs, interest expense, change in the Deferred Purchase Price Obligation fair value and income tax expense or benefit from segment adjusted EBITDA.

Segment adjusted EBITDA by reportable segment follows.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	29,292		$	30,285		$	34,011
Ohio Gathering		39,126			39,969			41,246
Williston Basin		69,437			76,701			66,413
DJ Basin		18,668			7,558			6,624
Permian Basin		(879	)		(1,200	)		—
Piceance Basin		98,765			111,042			111,113
Barnett Shale		43,043			43,268			46,232
Marcellus Shale		20,051			24,267			23,888
Total of reportable segments' measures of profit	$	317,503		$	331,890		$	329,527

A reconciliation of income or loss before income taxes and income or loss from equity method investees to total of reportable segments' measures of profit or loss follows.

	Year ended December 31,
	2019			2018			2017
	(In thousands)
Reconciliation of (loss) income before income taxes and loss from equity method investees to total of reportable segments' measures of profit:
(Loss) income before income taxes and loss from equity method investees	$	(30,808	)	$	53,272		$	88,614
Add:
Corporate and Other expense		40,639			38,917			39,140
Interest expense		74,429			60,535			68,131
Early extinguishment of debt		—			—			22,039
Deferred Purchase Price Obligation		(1,982	)		20,975			(200,322	)
Depreciation and amortization		111,426			106,767			114,872
Proportional adjusted EBITDA for equity method investees		39,126			39,969			41,246
Adjustments related to MVC shortfall payments		3,476			(3,632	)		(41,373	)
Adjustments related to capital reimbursement activity		(2,156	)		(427	)		—
Unit-based and noncash compensation		8,171			8,328			7,951
(Gain) loss on asset sales, net		(1,536	)		—			527
Long-lived asset impairment		60,507			7,186			188,702
Goodwill impairment		16,211			—			—
Total of reportable segments' measures of profit	$	317,503		$	331,890		$	329,527

For the years ended December 31, 2019 and 2018, adjustments related to MVC shortfall payments recognize the earnings from MVC shortfall payments ratably over the term of the associated MVC (see Note 3).

Contributions in aid of construction are recognized over the remaining term of the respective contract. We include adjustments related to capital reimbursement activity in our calculation of segment adjusted EBITDA to account for revenue recognized from contributions in aid of construction.

For the year ended December 31, 2017, we included adjustments related to MVC shortfall payments in our calculation of segment adjusted EBITDA to account for (i) the net increases or decreases in deferred revenue for MVC shortfall payments and (ii) our inclusion of expected annual MVC shortfall payments. With respect to the impact of a net change in deferred revenue for MVC shortfall payments, we treated increases in deferred revenue balances as a favorable adjustment to segment adjusted EBITDA, while decreases in deferred revenue balances were treated as an unfavorable adjustment to segment adjusted EBITDA. We also included a proportional amount of any historical and expected MVC shortfall payments in each quarter prior to the quarter in which we actually recognize the shortfall payment.

Adjustments related to MVC shortfall payments by reportable segment follow.

	Year ended December 31, 2019
	Williston Basin		Piceance Basin			Barnett Shale		Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	—	$	(103	)	$	3,579	$	3,476

	Year ended December 31, 2018
	Williston Basin		Piceance Basin		Barnett Shale			Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	—	$	10	$	(3,642	)	$	(3,632	)

	Year Ended December 31, 2017
	Williston Basin			Piceance Basin			Barnett Shale			Total
	(In thousands)
Adjustments related to MVC shortfall payments:
Net change in deferred revenue for MVC shortfall payments	$	(37,693	)	$	(3,065	)	$	—		$	(40,758	)
Expected MVC shortfall adjustments		—			(3	)		(612	)		(615	)
Total adjustments related to MVC shortfall payments	$	(37,693	)	$	(3,068	)	$	(612	)	$	(41,373	)

SEGMENT INFORMATION - Reconciliation of Net Income (Loss) to Adjusted EBITDA (Details) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting [Abstract]
(Loss) income before income taxes and loss from equity method investees		$ (30,808,000)	$ 53,272,000	$ 88,614,000
Add:
Corporate and Other expense		40,639,000	38,917,000	39,140,000
Interest expense		74,429,000	60,535,000	68,131,000
Early extinguishment of debt		0	0	22,039,000
Deferred Purchase Price Obligation		(1,982,000)	20,975,000	(200,322,000)
Depreciation and amortization		111,426,000	106,767,000	114,872,000
Proportional adjusted EBITDA for equity method investees		39,126,000	39,969,000	41,246,000
Adjustments related to MVC shortfall payments		3,476,000	(3,632,000)	(41,373,000)
Adjustments related to capital reimbursement activity		(2,156,000)	(427,000)	0
Unit-based and noncash compensation		8,171,000	8,328,000	7,951,000
(Gain) loss on asset sales, net		(1,536,000)	0	527,000
Long-lived asset impairment		60,507,000	7,186,000	188,702,000
Goodwill impairment	$ 16,200,000	16,211,000	0	0
Total of reportable segments' measures of profit		$ 317,503,000	$ 331,890,000	$ 329,527,000

UNIT-BASED AND NONCASH COMPENSATION - SMLP Long-Term Incentive Plan (Details) - SMLP LTIP - Phantom Units - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Units
Nonvested units(in shares)	864,124	749,274	691,955
Units granted (in shares)	1,913,099	515,358	371,972
Unit vested (in shares)	(602,617)	(359,016)	(293,222)
Units forfeited (in shares)	(68,611)	(41,492)	(21,431)
Nonvested units(in shares)	2,105,995	864,124	749,274
Weighted-average grant date fair value
Nonvested, Weighted-average grant date fair value, beginning (in dollars per unit)	$ 17.11	$ 20.07	$ 19.59
Units granted, Weighted-average grant date fair value (in dollars per unit)	6.48	15.25	22.50
Units vested, Weighted-average grant date fair value (in dollars per unit)	16.78	22.39	24.76
Units forfeited, Weighted-average grant date fair value (in dollars per unit)	12.87	17.27	20.07
Nonvested, Weighted-average grant date fair value, beginning (in dollars per unit)	$ 7.69	$ 17.11	$ 20.07

UNAUDITED QUARTERLY FINANCIAL DATA (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Quarterly Summarized Information on Consolidated Results of Operations

Summarized information on the consolidated results of operations for each of the quarters during the two-year period ended December 31, 2019, follows.

	Quarter ended
	December 31, 2019			September 30, 2019			June 30, 2019			March 31, 2019
	(In thousands, except per-unit amounts)
Total revenues	$	112,247		$	100,187		$	99,686		$	131,408

Net (loss) income attributable to SMLP	$	(327,083	)	$	(10,645	)	$	4,809		$	(36,914	)
Less net income and IDRs attributable to General Partner		—			—			—			12
Less net income attributable to Series A Preferred Units		7,125			7,125			7,125			7,125
Less net income attributable to Subsidiary Series A Preferred Units		58			—			—			—
Net loss attributable to common limited partners	$	(334,266	)	$	(17,770	)	$	(2,316	)	$	(44,051	)

Loss per limited partner unit:
Common unit - basic	$	(3.79	)	$	(0.21	)	$	(0.03	)	$	(0.58	)
Common unit - diluted	$	(3.79	)	$	(0.21	)	$	(0.03	)	$	(0.58	)

	Quarter ended
	December 31, 2018		September 30, 2018		June 30, 2018			March 31, 2018
	(In thousands, except per-unit amounts)
Total revenues	$	133,671	$	127,479	$	128,183		$	117,320

Net income (loss) attributable to SMLP	$	38,654	$	57,430	$	(49,971	)	$	(3,930	)
Less net income and IDRs attributable to General Partner		2,907		3,279		1,140			2,058
Less net income attributable to Series A Preferred Units		7,125		7,125		7,125			7,125
Net income (loss) attributable to common limited partners	$	28,622	$	47,026	$	(58,236	)	$	(13,113	)

Earnings (loss) per limited partner unit:
Common unit - basic	$	0.39	$	0.64	$	(0.79	)	$	(0.18	)
Common unit - diluted	$	0.39	$	0.64	$	(0.79	)	$	(0.18	)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Useful lives of Property, Plant and Equipment

Estimates of useful lives follow.

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

DISPOSITIONS, DROP DOWN TRANSACTIONS AND RESTRUCTURING - Red Rock Gathering Asset Disposition (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Dec. 02, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)			$ 102,111	$ 496	$ 2,300
Long-lived asset impairment			$ 60,507	$ 7,186	$ 188,702
Red Rock Gathering Company LLC \| Disposal, not discontinued operations \| Purchase and Sale Agreement
Business Acquisition [Line Items]
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)		$ 12,000
Long-lived asset impairment	$ 14,200

SEGMENT INFORMATION - Concentration Risk (Details) - Sales Revenue, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Counterparty A - Piceance Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	0.00%	0.00%
Counterparty B - Williston Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	10.00%	0.00%	13.00%
Counterparty C - Piceance Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	0.00%	10.00%	0.00%
Counterparty D - Barnet Shale
Segment Reporting Information [Line Items]
Concentration risk, percentage	0.00%	0.00%	0.00%

SUBSEQUENT EVENTS

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

SUBSEQUENT EVENTS

20. SUBSEQUENT EVENTS

We have evaluated subsequent events for recognition or disclosure in the consolidated financial statements and no events have occurred that require adjustment to or disclosure in the consolidated financial statements.

RELATED-PARTY TRANSACTIONS - Expenses Incurred by the General Partner and Reimbursed (Details) - General Partner - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operation and maintenance expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 28,643	$ 29,061	$ 27,450
General and administrative expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 32,222	$ 30,119	$ 30,899

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net (loss) income	$ (369,833,000)	$ 42,351,000	$ 86,050,000
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and amortization	111,426,000	106,767,000	114,872,000
Noncash lease expense	3,086,000	0	0
Amortization of debt issuance costs	4,411,000	4,285,000	4,158,000
Deferred Purchase Price Obligation	(1,982,000)	20,975,000	(200,322,000)
Unit-based and noncash compensation	8,171,000	8,328,000	7,951,000
Loss from equity method investees	337,851,000	10,888,000	2,223,000
Distributions from equity method investees	37,300,000	35,271,000	40,220,000
(Gain) loss on asset sales, net	(1,536,000)	0	527,000
Long-lived asset impairment	60,507,000	7,186,000	188,702,000
Goodwill impairment	16,211,000	0	0
Early extinguishment of debt	0	0	22,039,000
Write-off of debt issuance costs	0	0	302,000
Changes in operating assets and liabilities:
Accounts receivable	(4,334,000)	(21,535,000)	25,063,000
Trade accounts payable	(95,000)	81,000	(3,246,000)
Accrued expenses	(10,327,000)	9,464,000	1,110,000
Due from (to) affiliate	71,000	(848,000)	830,000
Deferred revenue, net	1,683,000	5,355,000	(40,758,000)
Ad valorem taxes payable	(1,525,000)	2,221,000	(2,259,000)
Accrued interest	25,000	(24,000)	(5,173,000)
Accrued environmental remediation, net	(2,284,000)	(3,808,000)	(4,109,000)
Other, net	(6,489,000)	972,000	(348,000)
Net cash provided by operating activities	182,337,000	227,929,000	237,832,000
Cash flows from investing activities:
Capital expenditures	(182,291,000)	(200,586,000)	(124,215,000)
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)	102,111,000	496,000	2,300,000
Contributions to equity method investees	0	(4,924,000)	(25,513,000)
Distributions from equity method investment	7,313,000	0	0
Investment in equity method investee	(18,316,000)	0	0
Purchase of noncontrolling interest	0	(10,981,000)	(797,000)
Other, net	313,000	(284,000)	(458,000)
Net cash used in investing activities	(90,870,000)	(216,279,000)	(148,683,000)
Cash flows from financing activities:
Distributions to unitholders	(116,624,000)	(180,705,000)	(179,103,000)
Borrowings under Revolving Credit Facility	369,000,000	289,000,000	247,500,000
Repayments under Revolving Credit Facility	(158,000,000)	(84,000,000)	(634,500,000)
Repayment of Deferred Purchase Price Obligation	(151,750,000)	0	0
Debt issuance costs	(499,000)	(344,000)	(16,390,000)
Payment of redemption and call premiums on senior notes	0	0	(17,932,000)
Proceeds from ATM Program common unit issuances, net of costs	0	0	17,078,000
Proceeds from issuance of Series A Preferred Units, net of costs	27,392,000	0	293,238,000
Contribution from General Partner	0	0	465,000
Issuance of senior notes	0	0	500,000,000
Tender and redemption of senior notes	0	0	(300,000,000)
Other, net	(4,491,000)	(4,186,000)	(3,128,000)
Net cash used in financing activities	(63,472,000)	(8,735,000)	(95,147,000)
Net change in cash, cash equivalents and restricted cash	27,995,000	2,915,000	(5,998,000)
Cash and cash equivalents, beginning of period	4,345,000	1,430,000	7,428,000
Cash and cash equivalents, end of period	32,340,000	4,345,000	1,430,000
Supplemental cash flow disclosures:
Cash interest paid	76,883,000	64,678,000	71,488,000
Less capitalized interest	6,974,000	8,497,000	2,579,000
Interest paid (net of capitalized interest)	69,909,000	56,181,000	68,909,000
Cash paid for taxes	150,000	175,000	0
Noncash investing and financing activities
Capital expenditures in trade accounts payable (period-end accruals)	19,846,000	33,750,000	11,792,000
DPPO partial settlement	51,750,000	0	0
Asset contribution to an equity method investment	23,643,000	0	0
Capital expenditures relating to contributions in aid of construction for Topic 606 day 1 adoption	0	33,123,000	0
Right-of-use assets relating to Topic 842	5,448,000	0	0
Series A Preferred Units
Cash flows from financing activities:
Distributions to unitholders	$ (28,500,000)	$ (28,500,000)	$ (2,375,000)

EARNINGS PER UNIT (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of earnings per limited partner unit

The following table details the components of EPU.

	Year ended December 31,
	2019			2018		2017
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net (loss) income among limited partner interests:
Net (loss) income attributable to limited partners	$	(369,845	)	$	32,799	$	75,485
Less net income attributable to Series A Preferred Units		28,500			28,500		3,563
Less net income attributable to Subsidiary Series A Preferred Units		58			—		—
Net (loss) income attributable to common limited partners	$	(398,403	)	$	4,299	$	71,922

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic		82,365			73,304		72,705
Effect of nonvested phantom units		—			311		342
Weighted-average common units outstanding – diluted		82,365			73,615		73,047

(Loss) earnings per limited partner unit:
Common unit – basic	$	(4.84	)	$	0.06	$	0.99
Common unit – diluted	$	(4.84	)	$	0.06	$	0.98

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		175			2		42

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Narrative (Details)	Dec. 31, 2019	Dec. 31, 2018
Percentage of ownership interest	38.50%	40.00%
Unrestricted Subsidiaries \| Permian Holdco
Percentage of ownership interest	70.00%

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on property, plant and equipment follow.

	December 31, 2019		December 31, 2018
	(In thousands)
Gathering and processing systems and related equipment	$	2,182,950	$	2,155,325
Construction in progress		78,716		137,920
Land and line fill		10,137		11,748
Other		53,129		45,853
Total		2,324,932		2,350,846
Less accumulated depreciation		442,681		387,133
Property, plant and equipment, net	$	1,882,251	$	1,963,713

Schedule of long-lived asset impairments

During 2019, 2018 and 2017, we recognized the following long-lived asset impairments, by segment.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Long-lived asset impairment:
Williston Basin	$	10	$	3,972	$	101,961
Piceance Basin		14,162		1,004		697
DJ Basin		34,913		9		—
Barnett Shale		9,629		—		—
Utica Shale		—		1,440		878
Permian Basin		726		761		—

Schedule of depreciation expense and capitalized interest costs

Depreciation expense and capitalized interest follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Depreciation expense	$	78,341	$	74,511	$	75,120
Capitalized interest		6,974		8,497		2,579

LEASES, COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 5,636	$ 5,344
Payments made	(2,284)	(3,808)
Additional accruals	1,299	4,100
Accrued environmental remediation, ending balance	$ 4,651	$ 5,636

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Parenthetical) (Details) - Summit Holdings - USD ($)	Dec. 31, 2019	Dec. 31, 2018
5.5% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Stated interest rate	5.50%	5.50%
Debt face amount	$ 300,000,000.0	$ 300,000,000.0
5.75% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Stated interest rate	5.75%	5.75%
Debt face amount	$ 500,000,000.0	$ 500,000,000.0

RELATED-PARTY TRANSACTIONS (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of related party transactions

Expenses incurred by the General Partner and reimbursed by us under our Partnership Agreement were as follows:

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Operation and maintenance expense	$	28,643	$	29,061	$	27,450
General and administrative expense		32,222		30,119		30,899

DEBT - Maturities (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Debt
2020	$ 0
2021	0
2022	977,000
2023	0
2024	0
Thereafter	500,000
Total long-term debt	$ 1,477,000

RELATED-PARTY TRANSACTIONS - Narrative (Details) - SMP Holdings	1 Months Ended
	Feb. 28, 2017 $ / shares shares
RELATED-PARTY TRANSACTIONS
Shares sold (in shares) \| shares	4,000,000
Sale price (in dollars per share) \| $ / shares	$ 24.00

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 78,341	$ 74,511	$ 75,120
Capitalized interest	$ 6,974	$ 8,497	$ 2,579

LEASES, COMMITMENTS AND CONTINGENCIES - Narrative (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) MMcf	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Agreement	Nov. 30, 2019 USD ($)
Loss Contingencies [Line Items]
Finance leases, term of contract			3 years
Lease agreements renewal periods				5 years
Lessee, operating lease, existence of residual value guarantee [true false]			false
Lessee, operating lease, residual value guarantee, Description			Our leases do not contain residual value guarantees.
Lessee, operating lease, assumptions and judgments, whether contract is or contains lease			Our significant assumptions or judgments include the determination of whether a contract contains a lease and the discount rate used in our lease liabilities.
Lessee, operating lease, assumptions and judgments, discount rate, description			The rate implicit in our lease contracts is not readily determinable. In determining the discount rate used in our lease liabilities, we analyzed certain factors in our incremental borrowing rate, including collateral assumptions and the term used. Our incremental borrowing rate on the Revolving Credit Facility was 4.55% at December 31, 2019, which reflects the fixed rate at which we could borrow a similar amount, for a similar term and with similar collateral as in the lease contracts at the commencement date.
Electric power \| MMcf	60
Cost of project	$ 7,800,000
Up front payment included in property, plant and equipment	$ 3,000,000.0
Additional cost to increase transmission line capacity		$ 4,300,000
Letter of credit initial term		1 year
Irrevocable letter of credit payable		$ 9,100,000
Letter of credit renew term		12 months
Future minimum sublease payment				$ 1,200
Business Interruption
Loss Contingencies [Line Items]
Recoveries recognized			$ 2,600,000
Property Recoveries
Loss Contingencies [Line Items]
Recoveries recognized			400,000
Revolving credit facility
Loss Contingencies [Line Items]
Finance operating Lease obligations not exceed consolidated total assets			$ 50,000,000
Percentage of operating lease incremental borrowing rate			4.55%
Irrevocable letter of credit payable			$ 9,100,000
Office Space
Loss Contingencies [Line Items]
Lessee, operating lease, existence of option to extend [true false]			true
Lessee, operating lease, option to extend			We have options to extend the lease term of certain office space in Texas, Colorado and West Virginia. The beginning of the noncancelable lease period for these leases ranged from 2014 to 2018 and the lease period ends between 2020 and 2028. These lease agreements contain between one and three options to renew the lease for a period of between two and five years. As of December 31, 2019, the exercise of the renewal options for these leases are not reasonably certain and, as a result, the payments associated with these renewals are not included in the measurement of the lease liability and ROU asset.
Equipment
Loss Contingencies [Line Items]
Lessee, operating lease, option to extend			We also have options to extend the lease term of certain compression equipment used at the Summit Utica gathering system. The beginning of the noncancelable lease period for these leases was 2017 and the lease period ends in 2020. Upon expiration of the noncancelable lease period, we have the option to renew the leases on a month-to-month basis; we therefore have not included any amounts attributable to renewals in the measurement.
Minimum \| Office Space
Loss Contingencies [Line Items]
Operating leases, term of contract			3 years
Operating lease, number of renewal terms \| Agreement			1
Lease agreements renewal periods			2 years
Minimum \| Equipment
Loss Contingencies [Line Items]
Operating leases, term of contract			3 years
Maximum \| Meadowlark Midstream Gathering System \| Principal Owner
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy			$ 25,000,000.0
Coverage from property and business interruption insurance policy			$ 200,000,000.0
Maximum \| Office Space
Loss Contingencies [Line Items]
Operating leases, term of contract			10 years
Operating lease, number of renewal terms \| Agreement			3
Lease agreements renewal periods			5 years
Maximum \| Equipment
Loss Contingencies [Line Items]
Operating leases, term of contract			4 years

DEFERRED REVENUE (Tables)

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

Rollforward of deferred revenue

A rollforward of current deferred revenue follows.

	Utica Shale		Williston Basin		DJ Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total current
	(In thousands)
Current deferred revenue, January 1, 2018	$	18	$	1,017	$	358	$	7,038	$	1,619	$	38	$	10,088
Additions		18		1,744		943		21,955		1,651		96		26,407
Less revenue recognized		18		1,347		562		21,377		1,628		96		25,028
Current deferred revenue, December 31, 2018		18		1,414		739		7,616		1,642		38		11,467
Additions		18		2,262		5,165		16,211		1,632		38		25,326
Less revenue recognized		18		1,743		3,044		16,813		1,644		38		23,300
Current deferred revenue, December 31, 2019	$	18	$	1,933	$	2,860	$	7,014	$	1,630	$	38	$	13,493

A rollforward of noncurrent deferred revenue follows.

	Utica Shale		Williston Basin		DJ Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total noncurrent
	(In thousands)
Noncurrent deferred, revenue, January 1, 2018	$	39	$	4,215	$	4,505	$	18,219	$	8,217	$	333	$	35,528
Additions		—		1,851		3,720		7,869		3,062		—		16,502
Less reclassification to current deferred revenue		18		1,673		941		8,146		1,651		97		12,526
Noncurrent deferred revenue, December 31, 2018		21		4,393		7,284		17,942		9,628		236		39,504
Additions		—		1,940		5,470		6,104		1,579		—		15,093
Less reclassification to current deferred revenue		18		2,699		5,165		6,336		1,632		38		15,888
Noncurrent deferred revenue, December 31, 2019	$	3	$	3,634	$	7,589	$	17,710	$	9,575	$	198	$	38,709

REVENUE - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
REVENUE - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue From Contract With Customer [Line Items]
Revenue, performance obligation, description of payment terms	Our services are typically billed on a monthly basis and we do not offer extended payment terms. We do not have contracts with financing components.
Receivables with customers	$ 90,400	$ 82,900
Contract assets included in accounts receivable	3,902	8,755	$ 0
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 10,100	$ 10,800

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,324,932	$ 2,350,846
Less accumulated depreciation	442,681	387,133
Property, plant and equipment, net	1,882,251	1,963,713
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,182,950	2,155,325
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	78,716	137,920
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,137	11,748
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 53,129	$ 45,853

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Balance Sheet (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 4,948,000	$ 4,345,000
Restricted cash	27,392,000
Accounts receivable	102,118,000	97,936,000
Other current assets	5,018,000	3,971,000
Total current assets	139,476,000	106,252,000
Property, plant and equipment, net	1,882,251,000	1,963,713,000
Intangible assets, net	232,278,000	273,416,000
Goodwill	0	16,211,000
Investment in equity method investees	309,728,000	649,250,000
Other noncurrent assets	9,718,000	11,720,000
Total assets	2,573,451,000	3,020,562,000	$ 2,894,793,000
Liabilities and Capital
Trade accounts payable	24,415,000	38,414,000
Accrued expenses	11,482,000	21,963,000
Due to affiliate	311,000	240,000
Deferred revenue	13,493,000	11,467,000	10,088,000
Ad valorem taxes payable	8,477,000	10,550,000
Accrued interest	12,311,000	12,286,000
Accrued environmental remediation	1,725,000	2,487,000
Other current liabilities	11,933,000	12,645,000
Total current liabilities	84,147,000	110,052,000
Long-term debt	1,470,299,000	1,257,731,000
Noncurrent Deferred Purchase Price Obligation	178,453,000	383,934,000
Noncurrent deferred revenue	38,709,000	39,504,000	35,528,000
Noncurrent accrued environmental remediation	2,926,000	3,149,000
Other noncurrent liabilities	7,951,000	4,968,000
Total liabilities	1,782,485,000	1,799,338,000
Total partners' capital	763,516,000	1,221,224,000	$ 1,389,669,000	$ 1,169,673,000
Total liabilities, mezzanine capital and partners' capital	2,573,451,000	3,020,562,000
Consolidation Adjustments
Assets
Due from affiliate	(812,852,000)	(593,384,000)
Total current assets	(812,852,000)	(593,384,000)
Property, plant and equipment, net	273,000
Investment in equity method investees	(274,000)
Investment in subsidiaries	(4,956,626,000)	(5,558,638,000)
Total assets	(5,769,479,000)	(6,152,022,000)
Liabilities and Capital
Due to affiliate	(776,766,000)	(586,072,000)
Total current liabilities	(776,766,000)	(586,072,000)
Total liabilities	(776,766,000)	(586,072,000)
Total partners' capital	(4,992,713,000)	(5,565,950,000)
Total liabilities, mezzanine capital and partners' capital	(5,769,479,000)	(6,152,022,000)
Mezzanine Capital
Liabilities and Capital
Subsidiary Series A Preferred Units (30,058 units issued and outstanding at December 31, 2019)	27,450,000
SMLP
Assets
Cash and cash equivalents	118,000	185,000
Accounts receivable	69,000	321,000
Other current assets	2,124,000	1,179,000
Total current assets	2,311,000	1,685,000
Property, plant and equipment, net	6,420,000	5,813,000
Other noncurrent assets	3,152,000	3,183,000
Investment in subsidiaries	1,758,547,000	2,096,717,000
Total assets	1,770,430,000	2,107,398,000
Liabilities and Capital
Trade accounts payable	657,000	275,000
Accrued expenses	1,649,000	1,106,000
Due to affiliate	777,077,000	482,384,000
Ad valorem taxes payable	14,000	14,000
Other current liabilities	7,342,000	7,306,000
Total current liabilities	786,739,000	491,085,000
Noncurrent Deferred Purchase Price Obligation	178,453,000	383,934,000
Other noncurrent liabilities	5,635,000	3,843,000
Total liabilities	970,827,000	878,862,000
Total partners' capital	799,603,000	1,228,536,000
Total liabilities, mezzanine capital and partners' capital	1,770,430,000	2,107,398,000
Co-Issuers
Assets
Cash and cash equivalents	611,000	230,000
Due from affiliate	36,300,000
Total current assets	36,911,000	230,000
Other noncurrent assets	6,167,000	8,511,000
Investment in subsidiaries	3,198,079,000	3,461,921,000
Total assets	3,241,157,000	3,470,662,000
Liabilities and Capital
Due to affiliate		103,928,000
Accrued interest	12,311,000	12,286,000
Total current liabilities	12,311,000	116,214,000
Long-term debt	1,470,299,000	1,257,731,000
Total liabilities	1,482,610,000	1,373,945,000
Total partners' capital	1,758,547,000	2,096,717,000
Total liabilities, mezzanine capital and partners' capital	3,241,157,000	3,470,662,000
Guarantor Subsidiaries
Assets
Cash and cash equivalents	4,110,000	3,930,000
Accounts receivable	102,049,000	97,615,000
Other current assets	2,894,000	2,792,000
Due from affiliate	776,552,000	593,384,000
Total current assets	885,605,000	697,721,000
Property, plant and equipment, net	1,875,558,000	1,948,280,000
Intangible assets, net	232,278,000	273,416,000
Goodwill		16,211,000
Investment in equity method investees	275,000,000	649,250,000
Other noncurrent assets	29,000	26,000
Total assets	3,268,470,000	3,584,904,000
Liabilities and Capital
Trade accounts payable	23,758,000	35,831,000
Accrued expenses	9,536,000	20,857,000
Deferred revenue	13,493,000	11,467,000
Ad valorem taxes payable	8,463,000	10,536,000
Accrued environmental remediation	1,725,000	2,487,000
Other current liabilities	4,591,000	5,339,000
Total current liabilities	61,566,000	86,517,000
Noncurrent deferred revenue	38,709,000	39,504,000
Noncurrent accrued environmental remediation	2,926,000	3,149,000
Other noncurrent liabilities	2,316,000	1,125,000
Total liabilities	105,517,000	130,295,000
Total partners' capital	3,162,953,000	3,454,609,000
Total liabilities, mezzanine capital and partners' capital	3,268,470,000	3,584,904,000
Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	109,000
Restricted cash	27,392,000
Total current assets	27,501,000
Property, plant and equipment, net		9,620,000
Investment in equity method investees	35,002,000
Other noncurrent assets	370,000
Total assets	62,873,000	9,620,000
Liabilities and Capital
Trade accounts payable		2,308,000
Accrued expenses	297,000
Total current liabilities	297,000	2,308,000
Total liabilities	297,000	2,308,000
Total partners' capital	35,126,000	7,312,000
Total liabilities, mezzanine capital and partners' capital	62,873,000	$ 9,620,000
Non-Guarantor Subsidiaries \| Mezzanine Capital
Liabilities and Capital
Subsidiary Series A Preferred Units (30,058 units issued and outstanding at December 31, 2019)	$ 27,450,000

REVENUE

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

REVENUE

3. REVENUE

The majority of our revenue is derived from long-term, fee-based contracts with our customers, which include original terms of up to 25 years. We recognize revenue earned from fee-based gathering, compression, treating and processing services in gathering services and related fees. We also earn revenue in the Williston Basin and Permian Basin reporting segments from the sale of physical natural gas purchased from our customers under certain percent-of-proceeds arrangements. Under ASC Topic 606, these gathering contracts are presented net within cost of natural gas and NGLs. We sell natural gas that we retain from certain customers in the Barnett Shale reporting segment to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate and NGLs retained from certain of our gathering services in the Piceance Basin and Permian Basin reporting segments. Revenues from the sale of natural gas and condensate are recognized in Natural gas, NGLs and condensate sales; the associated expense is included in Operation and maintenance expense. Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis, with the revenue component recognized in Other revenues.

The transaction price in our contracts is primarily based on the volume of natural gas, crude oil or produced water transferred by our gathering systems to the customer’s agreed upon delivery point multiplied by the contractual rate. For contracts that include MVCs, variable consideration up to the MVC will be included in the transaction price. For contracts that do not include MVCs, we do not estimate variable consideration because the performance obligations are completed and settled on a daily basis. For contracts containing noncash consideration such as fuel received in-kind, we measure the transaction price at the point of sale when the volume, mix and market price of the commodities are known.

We have contracts with MVCs that are variable and constrained. Contracts with greater than monthly MVCs are reviewed on a quarterly basis and adjustments to those estimates are made during each respective reporting period, if necessary.

The transaction price is allocated if the contract contains more than one performance obligation such as contracts that include MVCs. The transaction price allocated is based on the MVC for the applicable measurement period.

Performance obligations. The majority of our contracts have a single performance obligation which is either to provide gathering services (an integrated service) or sell natural gas, NGLs and condensate, which are both satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. We also have certain contracts with multiple performance obligations. They include an option for the customer to acquire additional services such as contracts containing MVCs. These performance obligations would also be satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. In these instances, we allocate the contract’s transaction price to each performance obligation using our best estimate of the standalone selling price of each service in the contract.

Performance obligations for gathering services are generally satisfied over time. We utilize either an output method (i.e., measure of progress) for guaranteed, stand-ready service contracts or an asset/system delivery time estimate for non-guaranteed, as-available service contracts.

Performance obligations for the sale of natural gas, NGLs and condensate are satisfied at a point in time. There are no significant judgments for these transactions because the customer obtains control based on an agreed upon delivery point.

Our services are typically billed on a monthly basis and we do not offer extended payment terms. We do not have contracts with financing components.

The following table presents estimated revenue expected to be recognized over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments.

We applied the practical expedient in paragraph 606-10-50-14 of Topic 606 for certain arrangements that we consider optional purchases (i.e., there is no enforceable obligation for the customer to make purchases) and those amounts are therefore excluded from the table.

	2020		2021		2022		2023		2024		Thereafter
	(In thousands)
Gathering services and related fees	$	122,055	$	102,127	$	84,736	$	66,693	$	50,608	$	59,602

Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. Ohio Gathering is excluded from the tables below due to equity method accounting. For more detailed information about reportable segments, see Note 4.

	Reportable Segments
	Year ended December 31, 2019
	Utica Shale		Williston Basin		DJ Basin		Permian Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products / services lines
Gathering services and related fees	$	31,926	$	77,626	$	21,940	$	3,610	$	121,357	$	47,862	$	24,471	$	328,792	$	(2,045	)	$	326,747
Natural gas, NGLs and condensate sales		—		16,461		389		16,383		7,954		17,147		—		58,334		28,660			86,994
Other revenues		2,065		11,564		3,721		310		4,327		6,793		—		28,780		1,007			29,787
Total	$	33,991	$	105,651	$	26,050	$	20,303	$	133,638	$	71,802	$	24,471	$	415,906	$	27,622		$	443,528

	Reportable Segments
	Year ended December 31, 2018
	Utica Shale		Williston Basin		DJ Basin		Permian Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products / services lines
Gathering services and related fees	$	35,233	$	79,606	$	11,251	$	115	$	135,810	$	59,030	$	29,573	$	350,618	$	(6,002	)	$	344,616
Natural gas, NGLs and condensate sales		—		31,840		371		843		14,800		2,523		—		50,377		84,457			134,834
Other revenues		—		12,204		3,672		—		4,909		6,712		—		27,497		(294	)		27,203
Total	$	35,233	$	123,650	$	15,294	$	958	$	155,519	$	68,265	$	29,573	$	428,492	$	78,161		$	506,653

Contract balances. Contract assets relate to our rights to consideration for work completed but not billed at the reporting date and consist of the estimated MVC shortfall payments expected from our customers and unbilled activity associated with contributions in aid of construction. Contract assets are transferred to trade receivables when the rights become unconditional. The following table provides information about contract assets from contracts with customers:

	December 31, 2019			December 31, 2018
	(In thousands)
Contract assets, beginning of period	$	8,755		$	—
Additions		18,077			26,403
Transfers out		(22,930	)		(17,648	)
Contract assets, end of period	$	3,902		$	8,755

As of December 31, 2019, receivables with customers totaled $90.4 million and contract assets totaled $3.9 million which were included in the Accounts receivable caption on the consolidated balance sheet.

As of December 31, 2018, receivables with customers totaled $82.9 million and contract assets totaled $8.8 million which were included in the Accounts receivable caption on the consolidated balance sheet.

Contract liabilities (deferred revenue) relate to the advance consideration received from customers primarily for contributions in aid of construction. We recognize contract liabilities under these arrangements in revenue over the contract period. For the years ended December 31, 2019 and 2018, we recognized $10.1 million and $10.8 million, respectively, of gathering services and related fees which was included in the contract liability balance as of the beginning of the period. See Note 9 for additional details.

DEBT (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Schedule of debt and capital leases

Debt consisted of the following:

	December 31, 2019			December 31, 2018
	(In thousands)
Summit Holdings' variable rate senior secured Revolving Credit Facility (4.55% at December 31, 2019 and 5.03% at December 31, 2018) due May 2022	$	677,000		$	466,000
Summit Holdings' 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(1,686	)		(2,362	)
Summit Holdings' 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(5,015	)		(5,907	)
Total long-term debt	$	1,470,299		$	1,257,731

(1) Issuance costs are being amortized over the life of the notes.

Schedule of maturities of long-term debt

The aggregate amount of debt maturing during each of the years after December 31, 2019 are as follows (in thousands):

2020	$	—
2021		—
2022		977,000
2023		—
2024		—
Thereafter		500,000
Total long-term debt	$	1,477,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

AMORTIZING INTANGIBLE ASSETS - Estimated Aggregate Annual Amortization Expected to be Recognized (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Intangible assets
2020	$ 31,901
2021	28,209
2022	25,142
2023	25,088
2024	$ 14,917

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Long-Lived Asset Impairments (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Long-lived asset impairment			$ 60,507	$ 7,186	$ 188,702
Williston Basin
Property, Plant and Equipment [Line Items]
Long-lived asset impairment	$ 3,900	$ 101,900	10	3,972	101,961
Piceance Basin
Property, Plant and Equipment [Line Items]
Long-lived asset impairment			14,162	1,004	697
DJ Basin
Property, Plant and Equipment [Line Items]
Long-lived asset impairment			34,913	9
Barnett Shale
Property, Plant and Equipment [Line Items]
Long-lived asset impairment			9,629
Utica Shale
Property, Plant and Equipment [Line Items]
Long-lived asset impairment				1,440	$ 878
Permian Basin
Property, Plant and Equipment [Line Items]
Long-lived asset impairment			$ 726	$ 761

REVENUE (Tables)

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments

	2020		2021		2022		2023		2024		Thereafter
	(In thousands)
Gathering services and related fees	$	122,055	$	102,127	$	84,736	$	66,693	$	50,608	$	59,602

Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments

	Reportable Segments
	Year ended December 31, 2019
	Utica Shale		Williston Basin		DJ Basin		Permian Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products / services lines
Gathering services and related fees	$	31,926	$	77,626	$	21,940	$	3,610	$	121,357	$	47,862	$	24,471	$	328,792	$	(2,045	)	$	326,747
Natural gas, NGLs and condensate sales		—		16,461		389		16,383		7,954		17,147		—		58,334		28,660			86,994
Other revenues		2,065		11,564		3,721		310		4,327		6,793		—		28,780		1,007			29,787
Total	$	33,991	$	105,651	$	26,050	$	20,303	$	133,638	$	71,802	$	24,471	$	415,906	$	27,622		$	443,528

	Reportable Segments
	Year ended December 31, 2018
	Utica Shale		Williston Basin		DJ Basin		Permian Basin		Piceance Basin		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products / services lines
Gathering services and related fees	$	35,233	$	79,606	$	11,251	$	115	$	135,810	$	59,030	$	29,573	$	350,618	$	(6,002	)	$	344,616
Natural gas, NGLs and condensate sales		—		31,840		371		843		14,800		2,523		—		50,377		84,457			134,834
Other revenues		—		12,204		3,672		—		4,909		6,712		—		27,497		(294	)		27,203
Total	$	35,233	$	123,650	$	15,294	$	958	$	155,519	$	68,265	$	29,573	$	428,492	$	78,161		$	506,653

Schedule of Contract with Customer Asset

The following table provides information about contract assets from contracts with customers:

	December 31, 2019			December 31, 2018
	(In thousands)
Contract assets, beginning of period	$	8,755		$	—
Additions		18,077			26,403
Transfers out		(22,930	)		(17,648	)
Contract assets, end of period	$	3,902		$	8,755

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Statement of Operations (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues		$ 112,247,000	$ 100,187,000	$ 99,686,000	$ 131,408,000	$ 133,671,000	$ 127,479,000	$ 128,183,000	$ 117,320,000	$ 443,528,000	$ 506,653,000	$ 488,741,000
Costs and expenses:
Cost of natural gas and NGLs										63,438,000	107,661,000	57,237,000
Operation and maintenance										97,587,000	96,878,000	93,882,000
General and administrative										54,139,000	52,877,000	54,681,000
Depreciation and amortization										110,206,000	107,100,000	115,475,000
Transaction costs										1,788,000	0	73,000
(Gain) loss on asset sales, net										(1,536,000)	0	527,000
Long-lived asset impairment										60,507,000	7,186,000	188,702,000
Goodwill impairment	$ 16,200,000									16,211,000	0	0
Total costs and expenses										402,340,000	371,702,000	510,577,000
Other income										451,000	(169,000)	298,000
Interest expense										(74,429,000)	(60,535,000)	(68,131,000)
Early extinguishment of debt										0	0	(22,039,000)
Deferred Purchase Price Obligation										1,982,000	(20,975,000)	200,322,000
(Loss) income before income taxes and loss from equity method investees										(30,808,000)	53,272,000	88,614,000
Income tax expense										(1,174,000)	(33,000)	(341,000)
Loss from equity method investees										(337,851,000)	(10,888,000)	(2,223,000)
Net (loss) income										(369,833,000)	42,351,000	86,050,000
Consolidation Adjustments
Costs and expenses:
Equity in earnings of consolidated subsidiaries										659,055,000	(190,984,000)	135,991,000
Net (loss) income										659,055,000	(190,984,000)	135,991,000
Gathering Services and Related Fees
Revenues:
Total revenues										326,747,000	344,616,000	394,427,000
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues										86,994,000	134,834,000	68,459,000
Other Revenues
Revenues:
Total revenues										29,787,000	27,203,000	25,855,000
SMLP
Costs and expenses:
Depreciation and amortization										2,604,000	1,743,000	1,101,000
Transaction costs										1,788,000		73,000
(Gain) loss on asset sales, net										9,000
Total costs and expenses										4,401,000	1,743,000	1,174,000
Other income										451,000	(169,000)	298,000
Deferred Purchase Price Obligation										1,982,000	(20,975,000)	200,322,000
(Loss) income before income taxes and loss from equity method investees										(1,968,000)	(22,887,000)	199,446,000
Income tax expense										(1,174,000)	(33,000)	(341,000)
Equity in earnings of consolidated subsidiaries										(366,691,000)	65,271,000	(113,055,000)
Net (loss) income										(369,833,000)	42,351,000	86,050,000
Co-Issuers
Costs and expenses:
Interest expense										(74,327,000)	(60,442,000)	(68,080,000)
Early extinguishment of debt												(22,039,000)
(Loss) income before income taxes and loss from equity method investees										(74,327,000)	(60,442,000)	(90,119,000)
Equity in earnings of consolidated subsidiaries										(292,364,000)	125,713,000	(22,936,000)
Net (loss) income										(366,691,000)	65,271,000	(113,055,000)
Guarantor Subsidiaries
Revenues:
Total revenues										443,528,000	506,653,000	488,741,000
Costs and expenses:
Cost of natural gas and NGLs										63,438,000	107,661,000	57,237,000
Operation and maintenance										97,587,000	96,878,000	93,882,000
General and administrative										54,139,000	52,877,000	54,681,000
Depreciation and amortization										107,602,000	105,357,000	114,374,000
(Gain) loss on asset sales, net										(1,545,000)		527,000
Long-lived asset impairment										60,507,000	7,186,000	188,702,000
Goodwill impairment										16,211,000
Total costs and expenses										397,939,000	369,959,000	509,403,000
Interest expense										(102,000)	(93,000)	(51,000)
(Loss) income before income taxes and loss from equity method investees										45,487,000	136,601,000	(20,713,000)
Loss from equity method investees										(336,950,000)	(10,888,000)	(2,223,000)
Net (loss) income										(291,463,000)	125,713,000	(22,936,000)
Guarantor Subsidiaries \| Gathering Services and Related Fees
Revenues:
Total revenues										326,747,000	344,616,000	394,427,000
Guarantor Subsidiaries \| Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues										86,994,000	134,834,000	68,459,000
Guarantor Subsidiaries \| Other Revenues
Revenues:
Total revenues										29,787,000	$ 27,203,000	$ 25,855,000
Non-Guarantor Subsidiaries
Costs and expenses:
Loss from equity method investees										(901,000)
Net (loss) income										$ (901,000)

PROPERTY, PLANT, AND EQUIPMENT, NET

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT, NET

5. PROPERTY, PLANT AND EQUIPMENT, NET

Details on property, plant and equipment follow.

	December 31, 2019		December 31, 2018
	(In thousands)
Gathering and processing systems and related equipment	$	2,182,950	$	2,155,325
Construction in progress		78,716		137,920
Land and line fill		10,137		11,748
Other		53,129		45,853
Total		2,324,932		2,350,846
Less accumulated depreciation		442,681		387,133
Property, plant and equipment, net	$	1,882,251	$	1,963,713

During 2019, 2018 and 2017, we identified certain events, facts and circumstances which indicated that certain of our property, plant and equipment could be impaired. As such, we reviewed the assets that had been identified as potentially impaired and estimated the fair value of the identified property, plant and equipment using a market-based approach.

In December 2019, we sold certain Red Rock Gathering system assets for a cash purchase price of $12.0 million. Prior to closing, we recorded an impairment charge of $14.2 million based on the expected consideration and the carrying value for the Red Rock Gathering system assets. See Note 17 for additional details.

In December 2019, in connection with the cancellation of a project, we determined certain processing plant assets in the Permian Basin would no longer be utilized. As a result, we recorded an impairment charge of $0.7 million related to these assets in the fourth quarter of 2019. See Note 6 for additional details.

In March 2019, certain events occurred which indicated that certain long-lived assets in the DJ Basin and Barnett Shale reporting segments could be impaired. Consequently, in the first quarter of 2019, we performed a recoverability assessment of certain assets within these reporting segments.

In the DJ Basin, we determined that certain processing plant assets related to our existing 20 MMcf/d plant would no longer be utilized due to our expansion plans for the Niobrara G&P system. Based on the results of the recoverability assessment and the conclusion that the carrying value was not fully recoverable, we recorded an impairment charge of $34.7 million related to these assets in the first quarter of 2019.

In the Barnett Shale, we determined, in the first quarter of 2019, that certain compressor station assets would be shut down and decommissioned. As a result, we recorded an impairment charge of $9.7 million related to these assets in the first quarter of 2019. See Note 6 for additional details.

In December 2018, in connection with certain strategic initiatives, we performed a recoverability assessment of certain assets within the Williston Basin reporting segment. Based on the results, we concluded that the carrying value of certain long-lived assets related to the Tioga Midstream system within the Williston Basin were not fully recoverable. We recorded an impairment charge of $3.9 million related to these assets after comparing the fair value of the long-lived assets to their carrying values. In addition, we reviewed the other assets that had been identified as potentially impaired and recognized the long-lived asset impairments in the table below.

In December 2017, in connection with certain strategic initiatives, we performed a financial review of certain assets within the Williston Basin reporting segment. This resulted in a triggering event that required us to perform a recoverability test. Based on the results of the test, we concluded that the carrying value of certain long-lived assets related to the Bison Midstream system within the Williston Basin were not fully recoverable. We recorded an impairment charge of $101.9 million related to these assets after comparing the fair value of the long-lived assets to their carrying values. See Note 6 for additional details.

During 2019, 2018 and 2017, we recognized the following long-lived asset impairments, by segment.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Long-lived asset impairment:
Williston Basin	$	10	$	3,972	$	101,961
Piceance Basin		14,162		1,004		697
DJ Basin		34,913		9		—
Barnett Shale		9,629		—		—
Utica Shale		—		1,440		878
Permian Basin		726		761		—

Our impairment determinations, in the context of these reviews, involved significant assumptions and judgments. Differing assumptions regarding any of these inputs could have a significant effect on the various valuations. As such, the fair value measurements utilized within these estimates are classified as non-recurring Level 3 measurements in the fair value hierarchy because they are not observable from objective sources. Due to the volatility of the inputs used, we cannot predict the likelihood of any future impairment.

Depreciation expense and capitalized interest follow.

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Depreciation expense	$	78,341	$	74,511	$	75,120
Capitalized interest		6,974		8,497		2,579

LEASES, COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of right-of-use assets and lease liabilities

	December 31,
	2019
	(In thousands)

ROU assets
Operating	$	3,580
Finance		3,159
	$	6,739
Lease liabilities, current
Operating	$	1,221
Finance		1,246
	$	2,467
Lease liabilities, noncurrent
Operating	$	2,513
Finance		676
	$	3,189

Schedule of lease cost and other information

Lease cost and Other information follow:

	Year ended December 31, 2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	1,559
Interest on lease liabilities (included in interest expense)		102
Operating lease cost (included in general and administrative expense)		3,159
	$	4,820

	Twelve months ended
	December 31, 2019
	(In thousands)
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	3,396
Operating cash outflows from finance leases		102
Financing cash outflows from finance leases		1,873
ROU assets obtained in exchange for new operating lease liabilities		1,218
ROU assets obtained in exchange for new finance lease liabilities		1,350
Weighted-average remaining lease term (years) - operating leases		5.8
Weighted-average remaining lease term (years) - finance leases		2.0
Weighted-average discount rate - operating leases		5	%
Weighted-average discount rate - finance leases		4	%

Schedule of total rent expense related to operating leases

	Year ended December 31,
	2019		2018		2017
	(In thousands)
Lease expense	$	3,851	$	3,928	$	3,772

Future minimum lease payments due and future minimum rentals to be received under noncancelable leases and subleases

Future minimum lease payments due under noncancelable leases at December 31, 2019, were as follows

	December 31, 2019
	(In thousands)
	Operating		Finance
2020	$	1,705	$	1,299
2021		1,004		616
2022		551		76
2023		408		—
2024		240		—
2025		153		—
Thereafter		742		—
Total future minimum lease payments	$	4,803	$	1,991

Future minimum lease payments due under noncancelable operating leases

Future minimum lease payments due under noncancelable operating leases (under ASC 840) at December 31, 2018, were as follows:

	December 31,
	2018
	(In thousands)
2019	$	3,133
2020		1,018
2021		550
2022		506
2023		373
Thereafter		621
Total future minimum lease payments	$	6,201

Schedule of Future Payments Due Under Finance Leases

Future payments due under finance leases (under ASC 840) at December 31, 2018, were as follows:

	December 31,
	2018
	(In thousands)
2019	$	1,473
2020		902
2021		174
Total finance lease obligations		2,549
Less: Amounts representing interest		(104	)
Net present value of finance lease obligations		2,445
Less: Amount representing current portion (included in Other current liabilities)		(1,406	)
Finance lease obligations, less current portion (included in Other noncurrent liabilities)	$	1,039

Schedule of accrued environmental remediation

A rollforward of the aggregate accrued environmental remediation liabilities follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2018	$	5,344
Payments made		(3,808	)
Additional accruals		4,100
Accrued environmental remediation, December 31, 2018	$	5,636
Payments made		(2,284	)
Additional accruals		1,299
Accrued environmental remediation, December 31, 2019	$	4,651

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average remaining vesting period	1 year 7 months 6 days
Phantom Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
SMLP LTIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved for issuance (in shares)	5,000,000.0
Units remaining available	1,300,000
Unrecognized unit-based compensation \| $	$ 8.5

EQUITY METHOD INVESTMENTS - Balance Sheet Information (Details) - USD ($) $ in Thousands	Nov. 30, 2019	Nov. 30, 2018
OGC
Schedule Of Equity Method Investments [Line Items]
Current assets	$ 41,972	$ 37,403
Noncurrent assets	1,281,171	1,262,253
Total assets	1,323,143	1,299,656
Current liabilities	21,798	19,903
Noncurrent liabilities	4,113	3,688
Total liabilities	25,911	23,591
OCC
Schedule Of Equity Method Investments [Line Items]
Current assets	2,187	3,716
Noncurrent assets	28,323	27,203
Total assets	30,510	30,919
Current liabilities	4,016	3,912
Noncurrent liabilities	6,683	8,807
Total liabilities	$ 10,699	$ 12,719