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Three months ended March 31,

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Counterparty A - Piceance Basin

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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		82,695,311
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	SMLP

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 5,300	$ 4,345
Accounts receivable	91,978	97,936
Other current assets	2,812	3,971
Total current assets	100,090	106,252
Property, plant and equipment, net	1,873,929	1,963,713
Intangible assets, net	258,711	273,416
Goodwill	16,211	16,211
Investment in equity method investees	640,226	649,250
Other noncurrent assets	11,423	11,720
Total assets	2,900,590	3,020,562
Current liabilities:
Trade accounts payable	28,324	38,414
Accrued expenses	20,610	21,963
Due to affiliate	320	240
Deferred revenue	11,639	11,467
Ad valorem taxes payable	3,818	10,550
Accrued interest	15,397	12,286
Accrued environmental remediation	2,129	2,487
Other current liabilities	12,858	12,645
Deferred Purchase Price Obligation	100,000
Total current liabilities	195,095	110,052
Long-term debt	1,226,146	1,257,731
Noncurrent Deferred Purchase Price Obligation	288,361	383,934
Noncurrent deferred revenue	41,203	39,504
Noncurrent accrued environmental remediation	3,126	3,149
Other noncurrent liabilities	7,626	4,968
Total liabilities	1,761,557	1,799,338
Commitments and contingencies (Note 16)
Series A Preferred Units (300,000 units issued and outstanding at March 31, 2019 and December 31, 2018)	300,741	293,616
Common limited partner capital (82,695,311 units issued and outstanding at March 31, 2019 and 73,390,853 units issued and outstanding at December 31, 2018)	838,292	902,358
General Partner interests (zero units issued and outstanding at March 31, 2019 and 1,490,999 units issued and outstanding at December 31, 2018)		25,250
Total partners' capital	1,139,033	1,221,224
Total liabilities and partners' capital	$ 2,900,590	$ 3,020,562

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Series A preferred unitholders, issued	300,000	300,000
Series A preferred unitholders, outstanding	300,000	300,000
Common limited partner capital (in shares), issued	82,695,311	73,390,853
Common limited partner capital (in shares), outstanding	82,695,311	73,390,853
General partner interests (in shares), issued	0	1,490,999
General partner interests (in shares), outstanding	0	1,490,999

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Total revenues	$ 131,408	$ 117,320
Costs and expenses:
Cost of natural gas and NGLs	$ 31,759	$ 20,286
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 24,222	$ 24,604
General and administrative	17,281	14,385
Depreciation and amortization	27,727	26,677
Transaction costs	950	57
Gain on asset sales, net	(961)	(74)
Long-lived asset impairment	44,951	0
Total costs and expenses	145,929	85,935
Other income (expense), net	209	(7)
Interest expense	(17,527)	(15,122)
Deferred Purchase Price Obligation	(4,427)	(21,658)
Loss before income taxes and (loss) income from equity method investees	(36,266)	(5,402)
Income tax (expense) benefit	(207)	171
(Loss) income from equity method investees	(441)	1,386
Net loss	(36,914)	(3,845)
Net income attributable to noncontrolling interest	0	85
Net loss attributable to SMLP	(36,914)	(3,930)
Net income attributable to General Partner, including IDRs	12	2,058
Net loss attributable to limited partners	(36,926)	(5,988)
Series A Preferred Units
Costs and expenses:
Net loss attributable to limited partners	7,125	7,125
Common units
Costs and expenses:
Net loss attributable to limited partners	$ (44,051)	$ (13,113)
Loss per limited partner unit:
Basic (in dollars per share)	$ (0.58)	$ (0.18)
Diluted (in dollars per share)	$ (0.58)	$ (0.18)
Weighted-average limited partner units outstanding:
Basic (shares)	75,793	73,134
Diluted (shares)	75,793	73,134
Gathering Services and Related Fees
Revenues:
Total revenues	$ 86,964	$ 84,361
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	37,928	26,117
Other Revenues
Revenues:
Total revenues	$ 6,516	$ 6,842

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Adjustment	Noncontrolling interest	Noncontrolling interest Adjustment	Limited partners, Series A Preferred Units	Limited partners, Series A Preferred Units Adjustment	Common	Common Adjustment	General Partner	General Partner Adjustment
January 1, 2018 impact of Topic 606 day 1 adoption	$ 4,214		$ 0		$ 0		$ 4,130		$ 84
Beginning 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
Net income (loss)	(3,845)		85		7,125		(13,113)		2,058
Distributions to unitholders	(45,053)		0		0		(42,024)		(3,029)
Unit-based compensation	1,979		0		0		1,979		0
Tax withholdings on vested SMLP LTIP awards	(1,943)		0		0		(1,943)		0
Other	(940)		0		(810)		(130)		0
Ending balance at Mar. 31, 2018	1,344,081		$ 10,898		300,741		1,005,409		27,033
Beginning balance at Dec. 31, 2018	1,221,224				293,616		902,358		25,250
Net income (loss)	(36,914)				7,125		(44,051)		12
Conversion of General Partner economic interests	0				0		22,222		(22,222)
Distributions to unitholders	(45,281)				0		(42,241)		(3,040)
Unit-based compensation	2,526				0		2,526		0
Tax withholdings on vested SMLP LTIP awards	(2,522)				0		(2,522)		0
Ending balance at Mar. 31, 2019	$ 1,139,033				$ 300,741		$ 838,292		$ 0

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591552-111686

+ Details

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (36,914)	$ (3,845)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	28,116	26,526
Noncash lease expense	765	0
Amortization of debt issuance costs	1,080	1,040
Deferred Purchase Price Obligation	4,427	21,658
Unit-based and noncash compensation	2,526	1,962
(Loss) income from equity method investees	441	(1,386)
Distributions from equity method investees	8,583	9,644
Gain on asset sales, net	961	74
Long-lived asset impairment	44,951	0
Changes in operating assets and liabilities:
Accounts receivable	4,675	3,490
Trade accounts payable	271	(3,294)
Accrued expenses	(1,199)	1,472
Due from (to) affiliate	80	(645)
Deferred revenue, net	2,323	1,130
Ad valorem taxes payable	(6,184)	(4,495)
Accrued interest	3,111	3,073
Accrued environmental remediation, net	(548)	(360)
Other, net	(2,832)	(4,686)
Net cash provided by operating activities	52,711	51,210
Cash flows from investing activities:
Capital expenditures	(60,848)	(40,778)
Proceeds from asset sale (net of cash of $1,475)	89,461	0
Other, net	(120)	(221)
Net cash provided by (used in) investing activities	28,493	(40,999)
Cash flows from financing activities:
Distributions to unitholders	(45,281)	(45,053)
Borrowings under Revolving Credit Facility	69,000	50,000
Repayments under Revolving Credit Facility	(101,000)	(10,000)
Other, net	(2,968)	(3,222)
Net cash used in financing activities	(80,249)	(8,275)
Net change in cash and cash equivalents	955	1,936
Cash and cash equivalents, beginning of period	4,345	1,430
Cash and cash equivalents, end of period	5,300	3,366
Supplemental cash flow disclosures:
Cash interest paid	15,229	12,207
Less capitalized interest	1,915	1,222
Interest paid (net of capitalized interest)	13,314	10,985
Cash paid for taxes	0	0
Noncash investing and financing activities
Capital expenditures in trade accounts payable (period-end accruals)	23,389	19,943
Topic 606
Noncash investing and financing activities
Capital expenditures relating to contributions in aid of construction for day 1 adoption	0	33,123
Topic 842
Noncash investing and financing activities
Right-of-use assets relating to Topic 842	$ 5,448	$ 0

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Statement Of Cash Flows [Abstract]
Net of cash	$ 1,475

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

3 Months Ended

Mar. 31, 2019

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 the core producing areas of 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 (the “Equity Restructuring Agreement”) that was announced on February 26, 2019 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 March 31, 2019, SMP Holdings, a wholly owned subsidiary of Summit Investments, beneficially owned 34,604,581 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, 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 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;

•

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;

•

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 and eastern Utah;

•

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.

Additionally, until March 22, 2019, we owned Tioga Midstream, a crude oil, produced water and associated natural gas gathering system operating in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota. Refer to Note 17 for details on the sale of Tioga Midstream.

In February 2016, the Partnership and SMP Holdings, a wholly owned subsidiary of Summit Investments, entered into a contribution agreement (the "Contribution Agreement") pursuant to which SMP Holdings agreed to contribute to the Partnership substantially all of its limited partner interest in OpCo, a Delaware limited partnership that owns (i) 100% of the issued and outstanding membership interests of Summit Utica, Meadowlark Midstream and Tioga Midstream (collectively, the "Contributed Entities"), each a limited liability company and (ii) an equity ownership interest in each of OGC and OCC (collectively with OpCo and the Contributed Entities, the “2016 Drop Down Assets”) (the “2016 Drop Down”). The 2016 Drop Down closed in March 2016; concurrent therewith, a subsidiary of Summit Investments retained a 1% noncontrolling interest in OpCo. In a series of transactions in December 2017 and November 2018, we purchased the 1% noncontrolling interest in OpCo. As a result of these transactions, other than our investment in Ohio Gathering, all of our business activities are now conducted through wholly owned operating subsidiaries.

Presentation and Consolidation. We prepare our unaudited condensed 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 revenue and expense and the disclosure of contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates.

These unaudited condensed consolidated financial statements have been prepared pursuant to the rules and the regulations of the SEC. Certain information and note disclosures normally included in the annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. We believe that the disclosures made are adequate to make the information not misleading. In the opinion of management, the unaudited condensed consolidated financial statements contain all adjustments, including normal recurring adjustments, which are necessary to fairly present the unaudited condensed consolidated balance sheet as of March 31, 2019, the unaudited condensed consolidated statements of operations for the three months ended March 31, 2019 and 2018 and the unaudited condensed consolidated statements of partners’ capital and cash flows for the three months ended March 31, 2019 and 2018. The balance sheet at December 31, 2018 included herein was derived from our audited financial statements, but does not include all disclosures required by GAAP. See Note 2 for the impact relating to the adoption of the new lease standard. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto that are included in our annual report on Form 10-K for the year ended December 31, 2018, as filed with the SEC on February 26, 2019 (the "2018 Annual Report"). The results of operations for an interim period are not necessarily indicative of results expected for a full year.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Except for the changes below, there have been no changes to our significant accounting policies since December 31, 2018.

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 pronouncements:

•

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 unaudited condensed 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 unaudited condensed 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 March 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. We are currently evaluating the provisions of ASU 2018-13 to determine its impact on our financial statements and related disclosures and will adopt its provisions effective January 1, 2020.

REVENUE

3 Months Ended

Mar. 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 original terms of up to 25 years. We recognize revenue earned from fee-based gathering, treating and processing services in gathering services and related fees. We also earn revenue in the Williston Basin reporting segment 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 DFW Midstream customers to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate retained from our gathering services at Grand River. 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.

Certain of our gathering and/or processing agreements provide for monthly, annual or multi-year 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 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.

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 during the remainder of 2019 and 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 excluded from the table.

	2019		2020		2021		2022		2023		Thereafter
	(In thousands)
Gathering services and related fees	$	88,169	$	120,941	$	100,117	$	83,673	$	70,971	$	113,679

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
	Three months ended March 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	$	7,495	$	25,706	$	3,724	$	366	$	31,840	$	13,025	$	6,197	$	88,353	$	(1,389	)	$	86,964
Natural gas, NGLs and condensate sales		—		5,585		85		4,221		2,302		604		—		12,797		25,131			37,928
Other revenues		—		2,908		1,007		32		1,138		1,656		—		6,741		(225	)		6,516
Total	$	7,495	$	34,199	$	4,816	$	4,619	$	35,280	$	15,285	$	6,197	$	107,891	$	23,517		$	131,408

	Reportable Segments
	Three months ended March 31, 2018
	Utica Shale		Williston Basin		DJ 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	$	10,041	$	17,666	$	2,179	$	33,115	$	13,637	$	7,825	$	84,463	$	(102	)	$	84,361
Natural gas, NGLs and condensate sales		—		7,846		80		4,245		545		—		12,716		13,401			26,117
Other revenues		—		2,912		757		1,211		1,988		—		6,868		(26	)		6,842
Total	$	10,041	$	28,424	$	3,016	$	38,571	$	16,170	$	7,825	$	104,047	$	13,273		$	117,320

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:

	March 31, 2019			December 31, 2018
	(In thousands)
Contract assets, beginning of year	$	8,755		$	—
Additions		12,518			26,403
Transfers out		(1,959	)		(17,648	)
Contract assets, end of year	$	19,314		$	8,755

As of March 31, 2019, receivables with customers totaled $66.4 million and contract assets totaled $19.3 million which were included in the Accounts receivable caption on the unaudited condensed 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 three months ended March 31, 2019, we recognized $2.7 million 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.

SEGMENT INFORMATION

3 Months Ended

Mar. 31, 2019

Segment Reporting [Abstract]

SEGMENT INFORMATION

4. SEGMENT INFORMATION

As of March 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, Bison Midstream and Tioga Midstream (through March 22, 2019; refer to Note 17 for details on the sale of Tioga 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.

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 OGC and OCC. Income or loss from equity method investees, as reflected on the statements of operations, solely relates to Ohio Gathering and is recognized and disclosed on a one-month lag (see Note 8).

Corporate and Other represents those results that are: (i) not specifically attributable to a reportable segment; (ii) not individually reportable; 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, natural gas and crude oil marketing services and transaction costs.

Assets by reportable segment follow.

	March 31,2019			December 31, 2018
	(In thousands)
Assets (1):
Utica Shale	$	206,621		$	207,357
Ohio Gathering		640,226			649,250
Williston Basin		438,772			526,819
DJ Basin		150,663			166,580
Permian Basin		163,897			145,702
Piceance Basin		685,713			699,638
Barnett Shale		363,834			376,564
Marcellus Shale		206,447			208,790
Total reportable segment assets		2,856,173			2,980,700
Corporate and Other		47,238			44,181
Eliminations		(2,821	)		(4,319	)
Total assets	$	2,900,590		$	3,020,562

(1) At March 31, 2019 and December 31, 2018, Corporate and Other included $17.0 million and $9.6 million of capital expenditures relating to the Double E Pipeline Project.

Revenues by reportable segment follow.

	Three months ended March 31,
	2019			2018
	(In thousands)
Revenues (1):
Utica Shale	$	7,495		$	10,041
Williston Basin		34,199			28,424
DJ Basin		4,816			3,016
Permian Basin		4,619			—
Piceance Basin		35,280			38,571
Barnett Shale		15,285			16,170
Marcellus Shale		6,197			7,825
Total reportable segments revenue		107,891			104,047
Corporate and Other		26,838			14,176
Eliminations		(3,321	)		(903	)
Total revenues	$	131,408		$	117,320

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

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

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

* Less than 10%

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

	Three months ended March 31,
	2019		2018
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	1,908	$	1,853
Williston Basin		5,436		5,609
DJ Basin		799		781
Permian Basin		1,072		—
Piceance Basin		11,791		11,774
Barnett Shale (2)		4,330		3,757
Marcellus Shale		2,283		2,272
Total reportable segment depreciation and amortization		27,619		26,046
Corporate and Other		497		480
Total depreciation and amortization	$	28,116	$	26,526

(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 gas gathering contracts as reported in other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Three months ended March 31,
	2019			2018
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	101		$	1,020
Williston Basin		8,023			5,888
DJ Basin		28,356			14,260
Permian Basin		7,057			16,145
Piceance Basin		1,226			2,644
Barnett Shale (2)		(118	)		37
Marcellus Shale		102			487
Total reportable segment capital expenditures		44,747			40,481
Corporate and Other		16,101			297
Total cash paid for capital expenditures	$	60,848		$	40,778

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

(2) For the three months ended March 31, 2019, the amount includes vendor reimbursements of $1.1 million.

During the three months ended March 31, 2019, Corporate and Other included cash paid of $0.3 million for corporate purposes; the remainder represents capital expenditures relating to the Double E Pipeline 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 and (ix) other noncash expenses or losses, less other noncash income or gains. 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 (ii) amortization for deferred contract costs; multiplied by 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), 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.

	Three months ended March 31,
	2019			2018
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	6,193		$	8,715
Ohio Gathering		9,210			10,477
Williston Basin		18,734			15,970
DJ Basin		2,673			1,321
Permian Basin		(550	)		—
Piceance Basin		25,999			27,914
Barnett Shale		11,374			9,859
Marcellus Shale		5,142			6,676
Total of reportable segments' measures of profit or loss	$	78,775		$	80,932

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.

	Three months ended March 31,
	2019			2018
	(In thousands)
Reconciliation of loss before income taxes and loss from equity method investees to total of reportable segments' measures of profit:
Loss before income taxes and loss from equity method investees	$	(36,266	)	$	(5,402	)
Add:
Corporate and Other expense		14,159			10,623
Interest expense		17,527			15,122
Deferred Purchase Price Obligation		4,427			21,658
Depreciation and amortization		28,116			26,526
Proportional adjusted EBITDA for equity method investees		9,210			10,477
Adjustments related to MVC shortfall payments		(4,199	)		-
Adjustments related to capital reimbursement activity		(715	)		40
Unit-based and noncash compensation		2,526			1,962
Gain on asset sales, net		(961	)		(74	)
Long-lived asset impairment		44,951			-
Total of reportable segments' measures of profit	$	78,775		$	80,932

Adjustments related to MVC shortfall payments are recognized in gathering services and related fees (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.

Adjustments related to MVC shortfall payments by reportable segment follow.

	Three months ended March 31, 2019
	Williston Basin			Piceance Basin			Barnett Shale		Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	(5,549	)	$	(103	)	$	1,453	$	(4,199	)

There were no adjustments related to MVC shortfall payments for the three months ended March 31, 2018.

PROPERTY, PLANT, AND EQUIPMENT, NET

3 Months Ended

Mar. 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.

	March 31, 2019		December 31, 2018
	(In thousands)
Gathering and processing systems and related equipment	$	2,025,055	$	2,155,325
Construction in progress		169,987		137,920
Land and line fill		9,834		11,748
Other		53,873		45,853
Total		2,258,749		2,350,846
Less accumulated depreciation		384,820		387,133
Property, plant and equipment, net	$	1,873,929	$	1,963,713

In March 2019, certain events, facts and circumstances occurred which indicated that certain long-lived assets in the DJ Basin and Barnett Shale reporting segments could be impaired. Consequently, 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 Barnett Shale, we determined certain compressor station assets would be shut down and decommissioned beginning in the second quarter of 2019. As a result, we recorded an impairment charge of $9.7 million related to these assets. See Note 6 for additional details.

Depreciation expense and capitalized interest follow.

	Three months ended March 31,
	2019		2018
	(In thousands)
Depreciation expense	$	19,783	$	18,557
Capitalized interest		1,915		1,222

AMORTIZING INTANGIBLE ASSETS

3 Months Ended

Mar. 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:

	March 31, 2019
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(14,294	)	$	9,901
Contract intangibles		278,448		(150,180	)		128,268
Rights-of-way		158,862		(38,320	)		120,542
Total intangible assets	$	461,505	$	(202,794	)	$	258,711

	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 March 2019, certain events, facts and circumstances 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.

We recognized amortization expense in other revenues as follows:

	Three months ended March 31,
	2019			2018
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(389	)	$	(389	)

We recognized amortization expense in costs and expenses as follows:

	Three months ended March 31,
	2019		2018
	(In thousands)
Amortization expense – contract intangibles	$	6,397	$	6,535
Amortization expense – rights-of-way		1,547		1,585

The estimated aggregate annual amortization expected to be recognized for the remainder of 2019 and each of the four succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2019	$	24,063
2020		32,020
2021		28,328
2022		25,261
2023		25,207

GOODWILL

3 Months Ended

Mar. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

GOODWILL

7. GOODWILL

We evaluate goodwill for impairment annually on September 30. We also 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. There have been no impairments of goodwill during the three months ended March 31, 2019.

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, as discussed in the 2018 Annual Report. 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. Due to the volatility of the inputs used, we cannot predict the likelihood of any future impairment.

EQUITY METHOD INVESTMENTS

3 Months Ended

Mar. 31, 2019

Equity Method Investments And Joint Ventures [Abstract]

EQUITY METHOD INVESTMENTS

8. EQUITY METHOD INVESTMENTS

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.

As a result of our joint venture partner funding a disproportionate amount of the capital calls during the three months ended March 31, 2019, our ownership interest in Ohio Gathering decreased from 40.0% at December 31, 2018 to 39.5% at March 31, 2019.

A reconciliation of our 39.5% ownership interest in Ohio Gathering to our investment per Ohio Gathering's books and records follows (in thousands).

Investment in equity method investees, March 31, 2019	$	640,226
March cash distributions		2,883
Basis difference		(113,493	)
Investment in equity method investees, net of basis difference, February 28, 2019	$	529,616

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

	Three months ended February 28, 2019					Three months ended February 28, 2018
	OGC		OCC			OGC		OCC
	(In thousands)
Total revenues	$	33,466	$	2,266		$	34,960	$	2,489
Total operating expenses		25,487		2,973			26,775		2,141
Net income (loss)		7,972		(707	)		8,180		180

DEFERRED REVENUE

3 Months Ended

Mar. 31, 2019

Revenue From Contract With Customer [Abstract]

DEFERRED REVENUE

9. 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, 2019	$	18	$	1,414	$	739	$	7,616	$	1,642	$	38	$	11,467
Additions		5		350		393		5,222		409		9		6,388
Less revenue recognized		5		364		211		5,222		405		9		6,216
Current deferred revenue, March 31, 2019	$	18	$	1,400	$	921	$	7,616	$	1,646	$	38	$	11,639

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, 2019	$	21	$	4,393	$	7,284	$	17,942	$	9,628	$	236	$	39,504
Additions		—		1,701		1,335		1,785		378		—		5,199
Less reclassification to current deferred revenue		5		787		393		1,897		409		9		3,500
Noncurrent deferred revenue, March 31, 2019	$	16	$	5,307	$	8,226	$	17,830	$	9,597	$	227	$	41,203

DEBT

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

DEBT

10. DEBT

Debt consisted of the following:

	March 31, 2019			December 31, 2018
	(In thousands)
Summit Holdings' variable rate senior secured Revolving Credit Facility (5.00% at March 31, 2019 and 5.03% at December 31, 2018) due May 2022	$	434,000		$	466,000
Summit Holdings' 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(2,195	)		(2,362	)
Summit Holdings' 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(5,659	)		(5,907	)
Total long-term debt	$	1,226,146		$	1,257,731

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

Revolving Credit Facility. Summit Holdings has a senior secured revolving credit facility which allows for revolving loans, letters of credit and swing line loans. The Revolving Credit Facility has a $1.25 billion borrowing capacity, matures in May 2022, and includes a $250.0 million accordion feature. Bison Midstream and its subsidiaries, Grand River and its subsidiary, DFW Midstream, Summit Marketing, Summit Permian, Permian Finance, Summit Niobrara, OpCo, Summit Utica, Meadowlark Midstream, Tioga Midstream (Refer to Note 17 for details on the sale of Tioga Midstream), Summit Permian II, Summit Permian Transmission and SMLP 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.

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 March 31, 2019, the applicable margin under LIBOR borrowings was 2.50% and the interest rate was 5.00%. The unused portion of the Revolving Credit Facility totaled $816.0 million (subject to a commitment fee of 0.50%).

As of March 31, 2019, we had $7.9 million of debt issuance costs attributable to our Revolving Credit Facility and related amendments which are included in noncurrent assets on the unaudited condensed consolidated balance sheet.

As of and during the three months ended March 31, 2019, we were in compliance with the Revolving Credit Facility's financial covenants. There were no defaults or events of default during the three months ended March 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 February 2017, the Co-Issuers completed a public offering of $500.0 million of 5.75% senior unsecured notes (the "5.75% Senior Notes") as described in the 2018 Annual Report.

Bison Midstream and its subsidiaries, Grand River and its subsidiary, DFW Midstream, Summit Marketing, Summit Permian, Permian Finance, Summit Niobrara, OpCo, Summit Utica, Meadowlark Midstream, Tioga Midstream (Refer to Note 17 for details on the sale of Tioga Midstream), Summit Permian II and Summit Permian Transmission (collectively 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 5.5% Senior Notes and the 5.75% 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.

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

FINANCIAL INSTRUMENTS

3 Months Ended

Mar. 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 and accounts receivable. We maintain our cash and cash equivalents 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, 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 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 44% of total accounts receivable as of March 31, 2019, compared with 39% as of December 31, 2018.

Fair Value. The carrying amount of cash and cash equivalents, accounts receivable and trade accounts payable reported on the 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 expected to be made 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 (see Note 17 for additional information).

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

	March 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)	$	297,805	$	296,500	$	297,638	$	286,625
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		494,341		470,417		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 estimated fair value for the Senior Notes is based on an average of nonbinding broker quotes as of March 31, 2019 and December 31, 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

PARTNERS' CAPITAL

3 Months Ended

Mar. 31, 2019

Equity [Abstract]

PARTNERS' CAPITAL

12. PARTNERS' 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, 2019		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		—		554,458		—
Units, March 31, 2019		300,000		82,695,311		—

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 (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. ECP continues to control the non-economic GP interest in SMLP.

At-the-market Program. In 2017, we executed an equity distribution agreement and filed a prospectus and a prospectus supplement 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"). These sales will be made (i) pursuant to the terms of the equity distribution agreement between us and the sales agents named therein and (ii) by means of ordinary brokers' transactions at market prices, in block transactions or as otherwise agreed between us and the sales agents. Sales of our common units may be made in negotiated transactions or transactions that are deemed to be at-the-market offerings as defined by SEC rules.

During the three months ended March 31, 2019, there were no transactions under the ATM Program. Following the effectiveness of the ATM Program registration statement and after taking into account the aggregate sales price of common units sold under the ATM Program through March 31, 2019, we have the capacity to issue additional common units under the ATM Program up to an aggregate $132.3 million.

Series A Preferred Units. In 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 as described in the 2018 Annual Report.

Cash Distributions Paid and Declared. We paid the following per-unit distributions during the three months ended March 31:

	Three months ended March 31,
	2019		2018
Per-unit distributions to unitholders	$	0.575	$	0.575

On April 25, 2019, the Board of Directors of our General Partner declared a distribution of $0.2875 per unit for the quarterly period ended March 31, 2019. This distribution, which totaled $23.8 million, will be paid on May 15, 2019 to unitholders of record at the close of business on May 8, 2019.

Incentive Distribution Rights. In March 2019, as a result of the Equity Restructuring, we cancelled our IDRs and converted our 2% economic GP interest to a non-economic GP interest in exchange for 8,750,000 newly issued SMLP common units, which were issued to SMP Holdings.

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.

For the three months ended March 31, 2018, our general partner held IDRs that entitled it to receive increasing percentage allocations, up to a maximum of 50%, of the cash we distributed from operating surplus in excess of $0.46 per unit per quarter.

Our payment of IDRs as reported in distributions to unitholders – general partner in the statement of partners' capital during the three months ended March 31 follow.

	Three months ended March 31,
	2019		2018
	(In thousands)
IDR payments	$	2,139	$	2,128

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 were recognized in the quarter in which they are paid.

EARNINGS PER UNIT

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

EARNINGS PER UNIT

13. EARNINGS PER UNIT

The following table details the components of EPU.

	Three months ended March 31,
	2019			2018
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net loss among limited partner interests:
Net loss attributable to limited partners	$	(36,926	)	$	(5,988	)
Less net income attributable to Series A Preferred Units		7,125			7,125
Net loss attributable to common limited partners	$	(44,051	)	$	(13,113	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic and diluted		75,793			73,134

Loss per limited partner unit:
Common unit – basic	$	(0.58	)	$	(0.18	)
Common unit – diluted	$	(0.58	)	$	(0.18	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		34			4

UNIT-BASED AND NONCASH COMPENSATION

3 Months Ended

Mar. 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. Items to note:

•

In March 2019, we granted 639,522 phantom units and associated distribution equivalent rights to employees in connection with our annual incentive compensation award cycle. These awards had a grant date fair value of $9.78 and vest ratably over a three-year period.

•

During the three months ended March 31, 2019, 559,364 phantom units vested.

•

As of March 31, 2019, approximately 2.6 million common units remained available for future issuance under the SMLP LTIP.

RELATED-PARTY TRANSACTIONS

3 Months Ended

Mar. 31, 2019

RELATED-PARTY TRANSACTIONS

15. RELATED-PARTY TRANSACTIONS

Acquisitions. See Notes 12 and 17 of the 2018 Annual Report.

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:

	Three months ended March 31,
	2019		2018
	(In thousands)
Operation and maintenance expense	$	7,885	$	7,623
General and administrative expense		10,830		8,117

LEASES, COMMITMENTS AND CONTINGENCIES

3 Months Ended

Mar. 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 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 changes 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 range from 2014 to 2018 and the lease period ends between 2019 and 2021. These lease agreements contain between one and three options to renew the lease for a period of between two and five years. As of March 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 is 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 the greater of $50 million or 5.5% of consolidated total assets in any period of twelve consecutive calendar months during the life of such leases.

During the three months ended March 31, 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 under development in the DJ Basin. The project is expected to cost approximately $7.8 million and we have made an up-front payment of $3.0 million which is included in the Property, plant and equipment, net caption on the unaudited condensed consolidated balance sheet. We have an unexercised option to increase the power needs of the transmission line up through June 30, 2019 for an additional cost. We will be required to provide an irrevocable letter of credit payable to the vendor with an initial term of one year totaling $4.8 million no later than June 30, 2019. 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 July 1, 2020.

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 5.03% at December 31, 2018, 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 unaudited condensed consolidated balance sheet) and lease liabilities (included in the Other current liabilities and Other noncurrent liabilities captions on our unaudited condensed consolidated balance sheet) follow:

	March 31,
	2019
	(In thousands)

ROU assets
Operating	$	4,683
Finance		3,721
	$	8,404
Lease liabilities, current
Operating	$	2,697
Finance		1,530
	$	4,227
Lease liabilities, noncurrent
Operating	$	2,197
Finance		1,163
	$	3,360

Lease cost and Other information follow:

	Three months ended
	March 31, 2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	368
Interest on lease liabilities (included in interest expense)		23
Operating lease cost (included in general and administrative expense)		832
	$	1,223
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	821
Operating cash outflows from finance leases		23
Financing cash outflows from finance leases		445
ROU assets obtained in exchange for new finance lease liabilities		693
Weighted-average remaining lease term (years) - operating leases		3.5
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:

	Three months ended March 31,
	2019		2018
	(In thousands)
Lease expense	$	944	$	1,022

Future minimum lease payments due under noncancelable leases for the remainder of 2019 and each of the five succeeding fiscal years, were as follows:

	March 31, 2019
	(In thousands)
	Operating		Finance
2019	$	3,193	$	1,234
2020		1,077		1,134
2021		555		406
2022		510		23
2023		373		—
2024		200		—
Thereafter		421		—
Total future minimum lease payments	$	6,329	$	2,797

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.

As described in the 2018 Annual Report, 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.

A rollforward of the aggregate accrued environmental remediation liabilities follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2019	$	5,636
Payments made		(548	)
Additional accruals		167
Accrued environmental remediation, March 31, 2019	$	5,255

As of March 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 March 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.

DISPOSITIONS, ACQUISITIONS AND DROP DOWN TRANSACTIONS

3 Months Ended

Mar. 31, 2019

Business Combinations [Abstract]

DISPOSITIONS, ACQUISITIONS AND DROP DOWN TRANSACTIONS

17. DISPOSITIONS, ACQUISITIONS AND DROP DOWN TRANSACTIONS

Tioga Midstream Disposition. In February 2019, Tioga Midstream, LLC, a subsidiary of SMLP, and certain affiliates of SMLP (collectively, “Summit”) 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 Summit 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, Summit 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 unaudited condensed consolidated statement of operations. The financial results of Tioga Midstream (a component of the Williston Basin reportable segment) are included in our unaudited condensed consolidated financial statements and footnotes for the period from January 1, 2019 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.

The present value of the Deferred Purchase Price Obligation is reflected as a liability on our balance sheet until paid. As of March 31, 2019, the Remaining Consideration which reflects the net present value of the $403.5 million Deferred Purchase Price Obligation as of March 31, 2019, was $388.4 million on the unaudited condensed consolidated balance sheet using a discount rate of 5.25%. We have presented $100 million of the Deferred Purchase Price Obligation as a current liability based on the cash payment mentioned herein which was made on April 1, 2019.

SUBSEQUENT EVENTS

3 Months Ended

Mar. 31, 2019

Subsequent Events [Abstract]

SUBSEQUENT EVENTS

18. SUBSEQUENT EVENTS

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

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Accounting Pronouncements

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

•

Refer to Note 16 for additional information.

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

•

Basis of Presentation

REVENUE (Tables)

3 Months Ended

Mar. 31, 2019

Revenue From Contract With Customer [Abstract]

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

	2019		2020		2021		2022		2023		Thereafter
	(In thousands)
Gathering services and related fees	$	88,169	$	120,941	$	100,117	$	83,673	$	70,971	$	113,679

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

	Reportable Segments
	Three months ended March 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	$	7,495	$	25,706	$	3,724	$	366	$	31,840	$	13,025	$	6,197	$	88,353	$	(1,389	)	$	86,964
Natural gas, NGLs and condensate sales		—		5,585		85		4,221		2,302		604		—		12,797		25,131			37,928
Other revenues		—		2,908		1,007		32		1,138		1,656		—		6,741		(225	)		6,516
Total	$	7,495	$	34,199	$	4,816	$	4,619	$	35,280	$	15,285	$	6,197	$	107,891	$	23,517		$	131,408

	Reportable Segments
	Three months ended March 31, 2018
	Utica Shale		Williston Basin		DJ 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	$	10,041	$	17,666	$	2,179	$	33,115	$	13,637	$	7,825	$	84,463	$	(102	)	$	84,361
Natural gas, NGLs and condensate sales		—		7,846		80		4,245		545		—		12,716		13,401			26,117
Other revenues		—		2,912		757		1,211		1,988		—		6,868		(26	)		6,842
Total	$	10,041	$	28,424	$	3,016	$	38,571	$	16,170	$	7,825	$	104,047	$	13,273		$	117,320

Schedule of Information about Contract Assets from Contracts with Customers

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

	March 31, 2019			December 31, 2018
	(In thousands)
Contract assets, beginning of year	$	8,755		$	—
Additions		12,518			26,403
Transfers out		(1,959	)		(17,648	)
Contract assets, end of year	$	19,314		$	8,755

SEGMENT INFORMATION (Tables)

3 Months Ended

Mar. 31, 2019

Segment Reporting [Abstract]

Schedule of assets by reportable segment

Assets by reportable segment follow.

	March 31,2019			December 31, 2018
	(In thousands)
Assets (1):
Utica Shale	$	206,621		$	207,357
Ohio Gathering		640,226			649,250
Williston Basin		438,772			526,819
DJ Basin		150,663			166,580
Permian Basin		163,897			145,702
Piceance Basin		685,713			699,638
Barnett Shale		363,834			376,564
Marcellus Shale		206,447			208,790
Total reportable segment assets		2,856,173			2,980,700
Corporate and Other		47,238			44,181
Eliminations		(2,821	)		(4,319	)
Total assets	$	2,900,590		$	3,020,562

(1) At March 31, 2019 and December 31, 2018, Corporate and Other included $17.0 million and $9.6 million of capital expenditures relating to the Double E Pipeline Project.

Schedule of segment reporting information

Revenues by reportable segment follow.

	Three months ended March 31,
	2019			2018
	(In thousands)
Revenues (1):
Utica Shale	$	7,495		$	10,041
Williston Basin		34,199			28,424
DJ Basin		4,816			3,016
Permian Basin		4,619			—
Piceance Basin		35,280			38,571
Barnett Shale		15,285			16,170
Marcellus Shale		6,197			7,825
Total reportable segments revenue		107,891			104,047
Corporate and Other		26,838			14,176
Eliminations		(3,321	)		(903	)
Total revenues	$	131,408		$	117,320

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

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

	Three months ended March 31,
	2019		2018
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	1,908	$	1,853
Williston Basin		5,436		5,609
DJ Basin		799		781
Permian Basin		1,072		—
Piceance Basin		11,791		11,774
Barnett Shale (2)		4,330		3,757
Marcellus Shale		2,283		2,272
Total reportable segment depreciation and amortization		27,619		26,046
Corporate and Other		497		480
Total depreciation and amortization	$	28,116	$	26,526

(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 gas gathering contracts as reported in other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Three months ended March 31,
	2019			2018
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	101		$	1,020
Williston Basin		8,023			5,888
DJ Basin		28,356			14,260
Permian Basin		7,057			16,145
Piceance Basin		1,226			2,644
Barnett Shale (2)		(118	)		37
Marcellus Shale		102			487
Total reportable segment capital expenditures		44,747			40,481
Corporate and Other		16,101			297
Total cash paid for capital expenditures	$	60,848		$	40,778

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

(2) For the three months ended March 31, 2019, the amount includes vendor 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:

(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.

	Three months ended March 31,
	2019			2018
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	6,193		$	8,715
Ohio Gathering		9,210			10,477
Williston Basin		18,734			15,970
DJ Basin		2,673			1,321
Permian Basin		(550	)		—
Piceance Basin		25,999			27,914
Barnett Shale		11,374			9,859
Marcellus Shale		5,142			6,676
Total of reportable segments' measures of profit or loss	$	78,775		$	80,932

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.

	Three months ended March 31,
	2019			2018
	(In thousands)
Reconciliation of loss before income taxes and loss from equity method investees to total of reportable segments' measures of profit:
Loss before income taxes and loss from equity method investees	$	(36,266	)	$	(5,402	)
Add:
Corporate and Other expense		14,159			10,623
Interest expense		17,527			15,122
Deferred Purchase Price Obligation		4,427			21,658
Depreciation and amortization		28,116			26,526
Proportional adjusted EBITDA for equity method investees		9,210			10,477
Adjustments related to MVC shortfall payments		(4,199	)		-
Adjustments related to capital reimbursement activity		(715	)		40
Unit-based and noncash compensation		2,526			1,962
Gain on asset sales, net		(961	)		(74	)
Long-lived asset impairment		44,951			-
Total of reportable segments' measures of profit	$	78,775		$	80,932

Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments

Adjustments related to MVC shortfall payments by reportable segment follow.

	Three months ended March 31, 2019
	Williston Basin			Piceance Basin			Barnett Shale		Total
	(In thousands)
Adjustments related to expected MVC shortfall payments:	$	(5,549	)	$	(103	)	$	1,453	$	(4,199	)

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

3 Months Ended

Mar. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on property, plant and equipment follow.

	March 31, 2019		December 31, 2018
	(In thousands)
Gathering and processing systems and related equipment	$	2,025,055	$	2,155,325
Construction in progress		169,987		137,920
Land and line fill		9,834		11,748
Other		53,873		45,853
Total		2,258,749		2,350,846
Less accumulated depreciation		384,820		387,133
Property, plant and equipment, net	$	1,873,929	$	1,963,713

Schedule of depreciation expense and capitalized interest costs

Depreciation expense and capitalized interest follow.

	Three months ended March 31,
	2019		2018
	(In thousands)
Depreciation expense	$	19,783	$	18,557
Capitalized interest		1,915		1,222

AMORTIZING INTANGIBLE ASSETS (Tables)

3 Months Ended

Mar. 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:

	March 31, 2019
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(14,294	)	$	9,901
Contract intangibles		278,448		(150,180	)		128,268
Rights-of-way		158,862		(38,320	)		120,542
Total intangible assets	$	461,505	$	(202,794	)	$	258,711

	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:

	Three months ended March 31,
	2019			2018
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(389	)	$	(389	)

We recognized amortization expense in costs and expenses as follows:

	Three months ended March 31,
	2019		2018
	(In thousands)
Amortization expense – contract intangibles	$	6,397	$	6,535
Amortization expense – rights-of-way		1,547		1,585

Estimated aggregate annual amortization expected to be recognized

The estimated aggregate annual amortization expected to be recognized for the remainder of 2019 and each of the four succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2019	$	24,063
2020		32,020
2021		28,328
2022		25,261
2023		25,207

EQUITY METHOD INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2019

Equity Method Investments And Joint Ventures [Abstract]

Equity Method Investments

A reconciliation of our 39.5% ownership interest in Ohio Gathering to our investment per Ohio Gathering's books and records follows (in thousands).

Investment in equity method investees, March 31, 2019	$	640,226
March cash distributions		2,883
Basis difference		(113,493	)
Investment in equity method investees, net of basis difference, February 28, 2019	$	529,616

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

	Three months ended February 28, 2019					Three months ended February 28, 2018
	OGC		OCC			OGC		OCC
	(In thousands)
Total revenues	$	33,466	$	2,266		$	34,960	$	2,489
Total operating expenses		25,487		2,973			26,775		2,141
Net income (loss)		7,972		(707	)		8,180		180

DEFERRED REVENUE (Tables)

3 Months Ended

Mar. 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, 2019	$	18	$	1,414	$	739	$	7,616	$	1,642	$	38	$	11,467
Additions		5		350		393		5,222		409		9		6,388
Less revenue recognized		5		364		211		5,222		405		9		6,216
Current deferred revenue, March 31, 2019	$	18	$	1,400	$	921	$	7,616	$	1,646	$	38	$	11,639

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, 2019	$	21	$	4,393	$	7,284	$	17,942	$	9,628	$	236	$	39,504
Additions		—		1,701		1,335		1,785		378		—		5,199
Less reclassification to current deferred revenue		5		787		393		1,897		409		9		3,500
Noncurrent deferred revenue, March 31, 2019	$	16	$	5,307	$	8,226	$	17,830	$	9,597	$	227	$	41,203

DEBT (Tables)

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Schedule of debt and capital leases

Debt consisted of the following:

	March 31, 2019			December 31, 2018
	(In thousands)
Summit Holdings' variable rate senior secured Revolving Credit Facility (5.00% at March 31, 2019 and 5.03% at December 31, 2018) due May 2022	$	434,000		$	466,000
Summit Holdings' 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(2,195	)		(2,362	)
Summit Holdings' 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(5,659	)		(5,907	)
Total long-term debt	$	1,226,146		$	1,257,731

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

- 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
-Publisher FASB
-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
-Topic 835
-SubTopic 30
-Section 45
-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
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-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
-SubTopic 10
-Section 50
-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

FINANCIAL INSTRUMENTS (Tables)

3 Months Ended

Mar. 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.

	March 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)	$	297,805	$	296,500	$	297,638	$	286,625
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		494,341		470,417		494,093		455,208

PARTNERS' CAPITAL (Tables)

3 Months Ended

Mar. 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, 2019		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		—		554,458		—
Units, March 31, 2019		300,000		82,695,311		—

Details of cash distributions

We paid the following per-unit distributions during the three months ended March 31:

	Three months ended March 31,
	2019		2018
Per-unit distributions to unitholders	$	0.575	$	0.575

Our payment of IDRs as reported in distributions to unitholders – general partner in the statement of partners' capital during the three months ended March 31 follow.

	Three months ended March 31,
	2019		2018
	(In thousands)
IDR payments	$	2,139	$	2,128

EARNINGS PER UNIT (Tables)

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Schedule of earnings per limited partner unit

The following table details the components of EPU.

	Three months ended March 31,
	2019			2018
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net loss among limited partner interests:
Net loss attributable to limited partners	$	(36,926	)	$	(5,988	)
Less net income attributable to Series A Preferred Units		7,125			7,125
Net loss attributable to common limited partners	$	(44,051	)	$	(13,113	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic and diluted		75,793			73,134

Loss per limited partner unit:
Common unit – basic	$	(0.58	)	$	(0.18	)
Common unit – diluted	$	(0.58	)	$	(0.18	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		34			4

RELATED-PARTY TRANSACTIONS (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of related party transactions

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

	Three months ended March 31,
	2019		2018
	(In thousands)
Operation and maintenance expense	$	7,885	$	7,623
General and administrative expense		10,830		8,117

LEASES, COMMITMENTS AND CONTINGENCIES (Tables)

3 Months Ended

Mar. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of right-of-use assets and lease liabilities

	March 31,
	2019
	(In thousands)

ROU assets
Operating	$	4,683
Finance		3,721
	$	8,404
Lease liabilities, current
Operating	$	2,697
Finance		1,530
	$	4,227
Lease liabilities, noncurrent
Operating	$	2,197
Finance		1,163
	$	3,360

Schedule of lease cost and other information

Lease cost and Other information follow:

	Three months ended
	March 31, 2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	368
Interest on lease liabilities (included in interest expense)		23
Operating lease cost (included in general and administrative expense)		832
	$	1,223
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	821
Operating cash outflows from finance leases		23
Financing cash outflows from finance leases		445
ROU assets obtained in exchange for new finance lease liabilities		693
Weighted-average remaining lease term (years) - operating leases		3.5
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

Lease expense related to operating leases, including lease expense incurred on our behalf and allocated to us, was as follows:

	Three months ended March 31,
	2019		2018
	(In thousands)
Lease expense	$	944	$	1,022

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 for the remainder of 2019 and each of the five succeeding fiscal years, were as follows:

	March 31, 2019
	(In thousands)
	Operating		Finance
2019	$	3,193	$	1,234
2020		1,077		1,134
2021		555		406
2022		510		23
2023		373		—
2024		200		—
Thereafter		421		—
Total future minimum lease payments	$	6,329	$	2,797

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, 2019	$	5,636
Payments made		(548	)
Additional accruals		167
Accrued environmental remediation, March 31, 2019	$	5,255

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - shares		1 Months Ended		3 Months Ended
	Feb. 26, 2019	Feb. 28, 2019	Feb. 29, 2016	Mar. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Dec. 31, 2017	Jun. 30, 2016
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)				82,695,311	73,390,853
Summit Midstream OpCo, LP
Organization And Business Operations [Line Items]
Ownership interest						1.00%	1.00%
SMP Holdings \| Contributed Entities
Organization And Business Operations [Line Items]
Percent of issued and outstanding membership interest			100.00%
Subsidiary of Summit Investments \| Summit Midstream OpCo, LP
Organization And Business Operations [Line Items]
Ownership interest								1.00%
Common units \| SMP Holdings
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)				34,604,581
Common units \| Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)				5,915,827
General Partner
Organization And Business Operations [Line Items]
General partner interest				2.00%
General Partner \| Summit Investments \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner interest	2.00%			2.00%
General Partner \| Common units
Organization And Business Operations [Line Items]
General partner units converted	8,750,000	8,750,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right-of-use asset	$ 4,683
Topic 842
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right-of-use asset		$ 5,400
Operating lease liability		$ 5,400

REVENUE - Narrative1 (Details)	Mar. 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

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
REVENUE - Narrative (Details) - USD ($) $ in Thousands	Mar. 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	$ 66,400
Contract assets included in accounts receivable	19,314	$ 8,755	$ 0
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 2,700

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) - Gathering Services and Related Fees $ in Thousands	Mar. 31, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
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	$ 88,169
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	$ 120,941
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	$ 100,117
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	$ 83,673
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	$ 70,971
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	21 years
Revenue, remaining performance obligation	$ 113,679

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Contract With Customer Asset And Liability [Abstract]
Contract assets, beginning of year	$ 8,755	$ 0
Additions	12,518	26,403
Transfers out	(1,959)	(17,648)
Contract assets, end of year	$ 19,314	$ 8,755

SEGMENT INFORMATION - Narrative (Details) - USD ($)	3 Months Ended
SEGMENT INFORMATION - Narrative (Details) - USD ($)	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Capital expenditures	$ 60,848,000	$ 40,778,000
Adjustments related to MVC shortfall payments	(4,199,000)	0
Barnett Shale
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	1,453,000
Corporate
Segment Reporting Information [Line Items]
Capital expenditures	300,000
Corporate and Other
Segment Reporting Information [Line Items]
Capital expenditures	17,000,000.0	9,600,000
Capital expenditures	16,101,000	297,000
Reportable Segments
Segment Reporting Information [Line Items]
Capital expenditures	44,747,000	40,481,000
Reportable Segments \| Barnett Shale
Segment Reporting Information [Line Items]
Cash paid for capital expenditures	1,100
Capital expenditures	$ (118,000)	$ 37,000

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets	$ 2,900,590		$ 3,020,562
Revenues	131,408	$ 117,320
Depreciation and amortization	28,116	26,526
Capital expenditures	60,848	40,778
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,856,173		2,980,700
Revenues	107,891	104,047
Depreciation and amortization	27,619	26,046
Capital expenditures	44,747	40,481
Reportable Segments \| Utica Shale
Segment Reporting Information [Line Items]
Assets	206,621		207,357
Revenues	7,495	10,041
Depreciation and amortization	1,908	1,853
Capital expenditures	101	1,020
Reportable Segments \| Ohio Gathering
Segment Reporting Information [Line Items]
Assets	640,226		649,250
Reportable Segments \| Williston Basin
Segment Reporting Information [Line Items]
Assets	438,772		526,819
Revenues	34,199	28,424
Depreciation and amortization	5,436	5,609
Capital expenditures	8,023	5,888
Reportable Segments \| DJ Basin
Segment Reporting Information [Line Items]
Assets	150,663		166,580
Revenues	4,816	3,016
Depreciation and amortization	799	781
Capital expenditures	28,356	14,260
Reportable Segments \| Barnett Shale
Segment Reporting Information [Line Items]
Assets	363,834		376,564
Revenues	15,285	16,170
Depreciation and amortization	4,330	3,757
Capital expenditures	(118)	37
Reportable Segments \| Permian Basin
Segment Reporting Information [Line Items]
Assets	163,897		145,702
Revenues	4,619
Depreciation and amortization	1,072
Capital expenditures	7,057	16,145
Reportable Segments \| Marcellus Shale
Segment Reporting Information [Line Items]
Assets	206,447		208,790
Revenues	6,197	7,825
Depreciation and amortization	2,283	2,272
Capital expenditures	102	487
Reportable Segments \| Piceance Basin
Segment Reporting Information [Line Items]
Assets	685,713		699,638
Revenues	35,280	38,571
Depreciation and amortization	11,791	11,774
Capital expenditures	1,226	2,644
Corporate and Other
Segment Reporting Information [Line Items]
Assets	47,238		44,181
Revenues	26,838	14,176
Depreciation and amortization	497	480
Capital expenditures	16,101	297
Eliminations
Segment Reporting Information [Line Items]
Assets	(2,821)		$ (4,319)
Revenues	$ (3,321)	$ (903)

SEGMENT INFORMATION - Concentration Risk (Details)	3 Months Ended
SEGMENT INFORMATION - Concentration Risk (Details)	Mar. 31, 2018
Sales Revenue, Net \| Customer Concentration Risk \| Counterparty A - Piceance Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 78,775	$ 80,932
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,193	8,715
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	9,210	10,477
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	18,734	15,970
DJ Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	2,673	1,321
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	11,374	9,859
Permian Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	(550)
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	5,142	6,676
Piceance Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 25,999	$ 27,914

SEGMENT INFORMATION - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting [Abstract]
Loss before income taxes and loss from equity method investees	$ (36,266,000)	$ (5,402,000)
Add:
Corporate and Other expense	14,159,000	10,623,000
Interest expense	17,527,000	15,122,000
Deferred Purchase Price Obligation	4,427,000	21,658,000
Depreciation and amortization	28,116,000	26,526,000
Proportional adjusted EBITDA for equity method investees	9,210,000	10,477,000
Adjustments related to MVC shortfall payments	(4,199,000)	0
Adjustments related to capital reimbursement activity	(715,000)	40,000
Unit-based and noncash compensation	2,526,000	1,962,000
Gain on asset sales, net	(961,000)	(74,000)
Long-lived asset impairment	44,951,000	0
Total of reportable segments' measures of profit	$ 78,775,000	$ 80,932,000

SEGMENT INFORMATION - Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	$ (4,199,000)	$ 0
Williston Basin
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	(5,549,000)
Piceance Basin
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	(103,000)
Barnett Shale
Segment Reporting Information [Line Items]
Adjustments related to MVC shortfall payments	$ 1,453,000

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,258,749	$ 2,350,846
Less accumulated depreciation	384,820	387,133
Property, plant and equipment, net	1,873,929	1,963,713
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,025,055	2,155,325
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	169,987	137,920
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,834	11,748
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 53,873	$ 45,853

PROPERTY, PLANT, AND EQUIPMENT, NET - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
DJ Basin
Property, Plant and Equipment [Line Items]
Asset impairment charges	$ 34.7
Barnett Shale
Property, Plant and Equipment [Line Items]
Asset impairment charges	$ 9.7

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 19,783	$ 18,557
Capitalized interest	$ 1,915	$ 1,222

AMORTIZING INTANGIBLE ASSETS - Intangible Assets and Liabilities Subject to Amortization (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 461,505	$ 468,852
Accumulated amortization	(202,794)	(195,436)
Net	258,711	273,416
Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24,195	24,195
Accumulated amortization	(14,294)	(13,905)
Net	9,901	10,290
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	278,448	278,448
Accumulated amortization	(150,180)	(143,962)
Net	128,268	134,486
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	158,862	166,209
Accumulated amortization	(38,320)	(37,569)
Net	$ 120,542	$ 128,640

AMORTIZING INTANGIBLE ASSETS (Narrative) (Details) $ in Millions	1 Months Ended
	Mar. 31, 2019 USD ($)
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Impairment charge for intangible assets	$ 0.5

AMORTIZING INTANGIBLE ASSETS - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Revenue \| Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (389)	$ (389)
Costs And Expenses \| Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,397	6,535
Costs And Expenses \| Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,547	$ 1,585

AMORTIZING INTANGIBLE ASSETS - Estimated Aggregate Annual Amortization Expected to be Recognized (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Intangible assets
2019	$ 24,063
2020	32,020
2021	28,328
2022	25,261
2023	$ 25,207

GOODWILL - Narrative (Details)	3 Months Ended
GOODWILL - Narrative (Details)	Mar. 31, 2019 USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

EQUITY METHOD INVESTMENTS - Narrative (Details)	Mar. 31, 2019	Dec. 31, 2018
OGC \| Principal Owner
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest	39.50%	40.00%

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018
Equity Method Investment [Roll Forward]
Investment in equity method investees, March 31, 2019	$ 640,226	$ 640,226
March cash distributions		8,583	$ 9,644
Investment in equity method investees, net of basis difference, February 28, 2019		649,250
OGC \| Summit Midstream Partners, LLC
Equity Method Investment [Roll Forward]
Investment in equity method investees, March 31, 2019	640,226	$ 640,226
March cash distributions	2,883
Basis difference	(113,493)
Investment in equity method investees, net of basis difference, February 28, 2019	$ 529,616

EQUITY METHOD INVESTMENTS - Statements of Operations Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2019	Feb. 28, 2018
OGC
Schedule Of Equity Method Investments [Line Items]
Total revenues	$ 33,466	$ 34,960
Total operating expenses	25,487	26,775
Net income (loss)	7,972	8,180
OCC
Schedule Of Equity Method Investments [Line Items]
Total revenues	2,266	2,489
Total operating expenses	2,973	2,141
Net income (loss)	$ (707)	$ 180

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 11,467
Current deferred revenue, Additions	6,388
Current deferred revenue, Less revenue recognized	6,216
Current deferred revenue, ending balance	11,639
Noncurrent deferred revenue, beginning balance	39,504
Noncurrent deferred revenue, Additions	5,199
Noncurrent deferred revenue, Less reclassification to current deferred revenue	3,500
Noncurrent deferred revenue, ending balance	41,203
Utica Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Current deferred revenue, Additions	5
Current deferred revenue, Less revenue recognized	5
Current deferred revenue, ending balance	18
Noncurrent deferred revenue, beginning balance	21
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	5
Noncurrent deferred revenue, ending balance	16
Williston Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,414
Current deferred revenue, Additions	350
Current deferred revenue, Less revenue recognized	364
Current deferred revenue, ending balance	1,400
Noncurrent deferred revenue, beginning balance	4,393
Noncurrent deferred revenue, Additions	1,701
Noncurrent deferred revenue, Less reclassification to current deferred revenue	787
Noncurrent deferred revenue, ending balance	5,307
Piceance Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	7,616
Current deferred revenue, Additions	5,222
Current deferred revenue, Less revenue recognized	5,222
Current deferred revenue, ending balance	7,616
Noncurrent deferred revenue, beginning balance	17,942
Noncurrent deferred revenue, Additions	1,785
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,897
Noncurrent deferred revenue, ending balance	17,830
DJ Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	739
Current deferred revenue, Additions	393
Current deferred revenue, Less revenue recognized	211
Current deferred revenue, ending balance	921
Noncurrent deferred revenue, beginning balance	7,284
Noncurrent deferred revenue, Additions	1,335
Noncurrent deferred revenue, Less reclassification to current deferred revenue	393
Noncurrent deferred revenue, ending balance	8,226
Barnett Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,642
Current deferred revenue, Additions	409
Current deferred revenue, Less revenue recognized	405
Current deferred revenue, ending balance	1,646
Noncurrent deferred revenue, beginning balance	9,628
Noncurrent deferred revenue, Additions	378
Noncurrent deferred revenue, Less reclassification to current deferred revenue	409
Noncurrent deferred revenue, ending balance	9,597
Marcellus Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Current deferred revenue, Additions	9
Current deferred revenue, Less revenue recognized	9
Current deferred revenue, ending balance	38
Noncurrent deferred revenue, beginning balance	236
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	9
Noncurrent deferred revenue, ending balance	$ 227

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Total long-term debt	$ 1,226,146	$ 1,257,731
SMP Holdings
Line of Credit Facility [Line Items]
Total long-term debt	1,226,146	1,257,731
SMP Holdings \| Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility	434,000	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	(2,195)	(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	$ (5,659)	$ (5,907)

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - SMP Holdings	Mar. 31, 2019	Dec. 31, 2018
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	5.00%	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%

DEBT - Revolving Credit Facility (Narrative) (Details) - Revolving credit facility	3 Months Ended
	Mar. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,250,000,000
Revolving credit facility maturity date	2022-05
Accordion feature	$ 250,000,000.0
Commitment fee on unused portion of the facility	0.50%
Interest rate at period end	5.00%
Unused portion under the facility	$ 816,000,000.0
Debt issuance costs	7,900,000
Debt defaults	$ 0
LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.50%
Minimum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility	0.30%
Minimum \| ABR
Line of Credit Facility [Line Items]
Applicable margin	0.75%
Minimum \| LIBOR
Line of Credit Facility [Line Items]
Applicable margin	1.75%
Maximum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility	0.50%
Maximum \| ABR
Line of Credit Facility [Line Items]
Applicable margin	1.75%
Maximum \| LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.75%

DEBT - Senior Notes (Narrative) (Details) - USD ($)		1 Months Ended
DEBT - Senior Notes (Narrative) (Details) - USD ($)	Jul. 31, 2014	Nov. 30, 2018	Jul. 31, 2014	Feb. 08, 2017
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%	5.75%
Debt face amount				$ 500,000,000.0
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
Finance Corp \| Summit Holdings
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary			100.00%

FINANCIAL INSTRUMENTS - Concentration Risk - Narrative (Details) - Customer	3 Months Ended	12 Months Ended
	Mar. 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	44.00%	39.00%

FINANCIAL INSTRUMENTS - Fair Value - Narrative (Details) - Drop Down Assets 2016 Acquisition - USD ($) $ in Millions	Mar. 31, 2020	Mar. 03, 2016	Jun. 30, 2020	Feb. 26, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Payments to Acquire Businesses, Gross		$ 360.0
Remaining cash consideration payable				$ 303.5
Scenario Forecast
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%
Scenario Forecast \| Minimum
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Minimum remaining consideration to be paid percentage			50.00%

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Carrying value \| 5.5% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 297,805	$ 297,638
Carrying value \| 5.75% Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	494,341	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	296,500	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	$ 470,417	$ 455,208

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Parenthetical) (Details) - Summit Holdings - USD ($)	Mar. 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

PARTNERS' CAPITAL - Partners' Capital and Schedule of Units (Details)	3 Months Ended
	Mar. 31, 2019 shares
Series A Preferred Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	300,000
Units, ending balance (in shares)	300,000
Conversion of General Partner economic interests (in shares)	0
Net units issued under the SMLP LTIP (in shares)	0
Common
Rollforwards of the number of partner units
Units, beginning balance (in shares)	73,390,853
Units, ending balance (in shares)	82,695,311
Conversion of General Partner economic interests (in shares)	8,750,000
Net units issued under the SMLP LTIP (in shares)	554,458
General Partner Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	1,490,999
Units, ending balance (in shares)	0
Conversion of General Partner economic interests (in shares)	(1,490,999)
Net units issued under the SMLP LTIP (in shares)	0

PARTNERS' CAPITAL - Narrative (Details) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended
	Apr. 25, 2019 USD ($) $ / shares	Mar. 22, 2019 USD ($) shares	Feb. 26, 2019 shares	Feb. 28, 2019 shares	Mar. 31, 2019 USD ($) Transaction $ / shares shares	Mar. 31, 2018 $ / shares	Dec. 31, 2018 shares	Dec. 31, 2017 USD ($) $ / shares shares
Partners Capital [Line Items]
Fair value					$ 0
Preferred units issued \| shares					300,000		300,000
Per-unit annual distributions to unitholders (in dollars per unit) \| $ / shares					$ 0.575	$ 0.575
Surplus in excess (in dollars per share) \| $ / shares					$ 0.46
Subsequent Event
Partners Capital [Line Items]
Per-unit annual distributions to unitholders (in dollars per unit) \| $ / shares	$ 0.2875
Cash paid to unit holders	$ 23,800
Cash distribution date	May 15, 2019
Cash distribution date of record	May 08, 2019
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued \| shares								300,000
Interest in partnership per unit \| $ / shares								$ 1,000
Summit Midstream Partners, LP \| Common units \| SMP Holdings
Partners Capital [Line Items]
General partner units converted \| shares		8,750,000
Fair value		$ 84,500
General Partner
Partners Capital [Line Items]
General partner interest					2.00%
Fair value					$ (22,222)
Percentage interest in distributions (maximum)					50.00%
General Partner \| Common units
Partners Capital [Line Items]
General partner units converted \| shares			8,750,000	8,750,000
General Partner \| Summit Midstream Partners, LP \| SMP Holdings
Partners Capital [Line Items]
General partner interest					2.00%
Common
Partners Capital [Line Items]
General partner units converted \| shares					8,750,000
Fair value					$ 22,222
Common \| Public Offering
Partners Capital [Line Items]
Aggregate offering price								$ 150,000
Transactions under ATM Program \| Transaction					0
Aggregate offering price					$ 132,300
Limited Partner \| Summit Midstream Partners, LP \| SMP Holdings
Partners Capital [Line Items]
Limited partner interest ownership percentage					41.80%
Limited Partner \| Summit Midstream Partners, LP \| Affiliate of Energy Capital Partners II, LLC
Partners Capital [Line Items]
Limited partner interest ownership percentage					7.20%

PARTNERS' CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.575	$ 0.575

PARTNERS' CAPITAL - Incentive Distribution Rights (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
IDR payments	$ 2,139	$ 2,128

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net loss attributable to limited partners	$ (36,926)	$ (5,988)
Phantom Units
Loss per limited partner unit:
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU (in shares)	34	4
Series A Preferred Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net loss attributable to limited partners	$ 7,125	$ 7,125
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net loss attributable to limited partners	$ (44,051)	$ (13,113)
Weighted-average common units outstanding – basic and diluted	75,793	73,134
Loss per limited partner unit:
Basic (in dollars per share)	$ (0.58)	$ (0.18)
Diluted (in dollars per share)	$ (0.58)	$ (0.18)

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) - SMLP LTIP	1 Months Ended	3 Months Ended
	Mar. 31, 2019 $ / shares shares	Mar. 31, 2019 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units remaining available	2,600,000	2,600,000
Phantom Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted units (in shares)	639,522
Grant date fair value (in dollars per share) \| $ / shares	$ 9.78
Vesting period	3 years
Units vested (in shares)		559,364

RELATED-PARTY TRANSACTIONS - Expenses Incurred by the General Partner and Reimbursed (Details) - General Partner - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operation and maintenance expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 7,885	$ 7,623
General and administrative expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 10,830	$ 8,117

LEASES, COMMITMENTS AND CONTINGENCIES - Narrative (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) Agreement MMcf	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Finance leases, term of contract	3 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 5.03% at December 31, 2018, 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
Letter of credit initial term	1 year
Irrevocable letter of credit payable	$ 4,800
Letter of credit renew term	12 months
Revolving credit facility
Loss Contingencies [Line Items]
Finance operating Lease obligations not exceed consolidated total assets	$ 50,000,000
Percentage of finance operating lease obligations not exceed consolidated total assets	5.50%
Percentage of operating lease incremental borrowing rate	5.03%
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 range from 2014 to 2018 and the lease period ends between 2019 and 2021. These lease agreements contain between one and three options to renew the lease for a period of between two and five years. As of March 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 is 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	$ 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

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Right of Use Assets and Lease Liabilities (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Right-of-use asset	$ 4,683
Finance	3,721
Total	8,404
Lease liabilities, current
Operating	2,697
Finance	1,530
Total	4,227
Lease liabilities, noncurrent
Finance	1,163
Total	3,360
Operating	$ 2,197

LEASES, COMMITMENTS AND CONTINGENCIES - Schedule of Lease Cost and Other Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$ 368
Interest on lease liabilities (included in interest expense)	23
Operating lease cost (included in general and administrative expense)	832
Total lease cost	1,223
Other information
Operating cash outflows from operating leases	821
Operating cash outflows from finance leases	23
Financing cash outflows from finance leases	445
ROU assets obtained in exchange for new finance lease liabilities	$ 693
Weighted-average remaining lease term (years) - operating leases	3 years 6 months
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%

LEASES, COMMITMENTS AND CONTINGENCIES - Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Lease expense	$ 944	$ 1,022

LEASES, COMMITMENTS AND CONTINGENCIES - Future Minimum Lease Payments Due and Future Minimum Rentals to be Received under Noncancelable Leases (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating lease, Future minimum lease payments, 2019	$ 3,193
Operating lease, Future minimum lease payments, 2020	1,077
Operating lease, Future minimum lease payments, 2021	555
Operating lease, Future minimum lease payments, 2022	510
Operating lease, Future minimum lease payments, 2023	373
Operating lease, Future minimum lease payments, 2024	200
Operating lease, Future minimum lease payments, Thereafter	421
Operating lease, Total future minimum lease payments	6,329
Finance lease, Future minimum lease payments, 2019	1,234
Finance lease, Future minimum lease payments, 2020	1,134
Finance lease, Future minimum lease payments, 2021	406
Finance lease, Future minimum lease payments, 2022	23
Finance lease, Total future minimum lease payments	$ 2,797

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

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

LEASES, COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 5,636
Payments made	(548)
Additional accruals	167
Accrued environmental remediation, ending balance	$ 5,255

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

DISPOSITIONS, ACQUISITIONS AND DROP DOWN TRANSACTIONS - 2016 Drop Down (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended
	Mar. 31, 2020	Mar. 03, 2016	Jun. 30, 2016	Mar. 31, 2019	Jun. 30, 2020	Apr. 01, 2019	Feb. 26, 2019
Business Acquisition [Line Items]
Deferred Purchase Price Obligation, current liability				$ 100,000
Drop Down Assets 2016 Acquisition
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 360,000
Working capital adjustment			$ 600
Remaining cash consideration payable							$ 303,500
Remaining consideration description				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
Estimated future payment obligation				$ 388,400
Deferred purchase price obligation				$ 403,500
Discount rate				5.25%
Drop Down Assets 2016 Acquisition \| Subsequent Event
Business Acquisition [Line Items]
Deferred Purchase Price Obligation, current liability						$ 100,000
Drop Down Assets 2016 Acquisition \| Scenario Forecast
Business Acquisition [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%
Drop Down Assets 2016 Acquisition \| Scenario Forecast \| Minimum
Business Acquisition [Line Items]
Minimum remaining consideration to be paid percentage					50.00%

REVENUE - Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Total revenues	$ 131,408	$ 117,320
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	23,517	13,273
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	107,891	104,047
Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,495	10,041
Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	34,199	28,424
Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,816	3,016
Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,619
Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	35,280	38,571
Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	15,285	16,170
Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,197	7,825
Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues		10,041
Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues		38,571
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues	86,964	84,361
Gathering Services and Related Fees \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	(1,389)	(102)
Gathering Services and Related Fees \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	88,353	84,463
Gathering Services and Related Fees \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,495
Gathering Services and Related Fees \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	25,706	17,666
Gathering Services and Related Fees \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	3,724	2,179
Gathering Services and Related Fees \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	366
Gathering Services and Related Fees \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	31,840
Gathering Services and Related Fees \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	13,025	13,637
Gathering Services and Related Fees \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,197	7,825
Gathering Services and Related Fees \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues		10,041
Gathering Services and Related Fees \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues		33,115
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues	37,928	26,117
Natural Gas, NGLs and Condensate Sales \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	25,131	13,401
Natural Gas, NGLs and Condensate Sales \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	12,797	12,716
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	5,585	7,846
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	85	80
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,221
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	2,302
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	604	545
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
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 \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues		4,245
Other Revenues
Disaggregation Of Revenue [Line Items]
Total revenues	6,516	6,842
Other Revenues \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	(225)	(26)
Other Revenues \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	6,741	6,868
Other Revenues \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0
Other Revenues \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	2,908	2,912
Other Revenues \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	1,007	757
Other Revenues \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	32
Other Revenues \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	1,138
Other Revenues \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	1,656	1,988
Other Revenues \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	$ 0	0
Other Revenues \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues		0
Other Revenues \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues		$ 1,211