0001564590-21-011012 | 10-K | XBRL Viewer | Summit Midstream Partners LP

$ 383,473

$ 443,528

Cost of natural gas and NGLs

$ 36,653

$ 63,438

Type of Cost, Good or Service [Extensible List]

us-gaap:OilAndGasPurchasedMember

Operation and maintenance

$ 86,030

$ 98,719

General and administrative

73,438

55,947

Depreciation and amortization

118,132

110,354

Transaction costs

2,993

3,017

Gain on asset sales, net

(307)

(1,536)

Long-lived asset impairment

13,089

60,507

Goodwill impairment

16,211

Total costs and expenses

330,028

406,657

Other income

451

Interest expense

(78,894)

(91,966)

Gain on early extinguishment of debt

203,062

Income (loss) before income taxes and equity method investment income (loss)

177,661

(54,644)

Income tax benefit (expense)

146

(1,231)

Income (loss) from equity method investees

11,271

(337,851)

Net income (loss)

189,078

(393,726)

Net income (loss) attributable to noncontrolling interest

(3,274)

(209,275)

Deemed contribution from preferred unit exchange and purchase

192,352

(184,451)

110,669

Series A Preferred Units

Deemed contribution from preferred unit exchange and purchase

26,529

28,500

54,945

Series A Preferred Units | Subsidiary

13,498

Common units

Net income (Loss) per limited partner unit:

$ 262,994

$ (213,009)

Basic (in dollars per share)

$ 73.22

$ (70.50)

Diluted (in dollars per share)

$ 71.19

$ (70.50)

Weighted-average limited partner units outstanding:

Basic (shares)

^[1]

3,592

3,021

Diluted (shares)

3,694

3,021

Gathering Services and Related Fees

Revenues:

Natural Gas, NGLs and Condensate Sales

$ 302,792

$ 326,747

Revenues:

49,319

86,994

Other Revenues

Revenues:

Beginning balance at Dec. 31, 2018

$ 31,362

$ 29,787

[1]	^{As a result of the GP Buy-In Transaction, our historical results are those of Summit Investments. The number of common units of 3.0 million as of December 31, 2019 represents those of Summit Investments and has been used for the earnings per unit calculation presented herein}

CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($)
$ in Thousands

Total

Partners' Capital

Series A Preferred Units

Noncontrolling Interest

Series A Preferred Units

Noncontrolling Interest

Common Noncontrolling Interest

^[1]

$ 1,391,567

$ 543,479

$ 293,616

$ 554,472

Net income (loss)

(393,784)

(213,009)

28,500

(209,275)

Net cash distribution to SMLP unitholders

(97,374)

(28,500)

(68,874)

Net cash distributions to Energy Capital Partners

(120,730)

Unit-based compensation

8,171

Effect of common unit issuances under SMLP LTIP

(2,664)

2,664

Tax withholdings and associated payments on vested SMLP LTIP awards

(2,614)

Conversion of noncontrolling interest related to cancellation of subsidiary incentive distribution rights

48,203

(48,203)

Conversion of noncontrolling interest related to partial cancellation of subsidiary of payable

50,271

(50,271)

Ending balance at Dec. 31, 2019

785,236

305,550

293,616

186,070

Net income (loss)

175,580

152,325

$ 14,654

11,875

(3,274)

Net cash distribution to SMLP unitholders

(6,037)

Unit-based compensation

8,111

4,057

4,054

Effect of common unit issuances under SMLP LTIP

(2,322)

2,322

Tax withholdings and associated payments on vested SMLP LTIP awards

(1,456)

(438)

(1,018)

Conversion of noncontrolling interest related to cancellation of subsidiary incentive distribution rights

110,669

Tax withholdings on Series A Preferred Unit Exchange

(237)

GP-Buy-In Transaction assumption of noncontrolling interest in SMLP

182,117

305,491

$ (305,491)

$ (182,117)

Repurchase of common units under GP Buy-In Transaction

(44,078)

Common unit issuance due to TL Restructuring

30,521

Effect of Exchange Offer and PreferredTender(2)

^[2]

(25,000)

120,720

(145,720)

Other

251

Ending balance at Dec. 31, 2020

$ 922,891

$ 748,466

$ 174,425

[1]	Prior to the GP Buy-in Transaction, common noncontrolling interests reported by Summit Investments included equity interests in SMLP that were not owned by Summit Investments.
[2]	⁽²⁾Includes deemed contributions of $54.9 million and $55.7 million related to the Exchange Offer and Tender Offer, respectively.

CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Deemed contribution from preferred unit exchange and purchase	$ 110,669
Exchanger Offer [Member]
Deemed contribution from preferred unit exchange and purchase	54,900
Tender Offer [Member]
Deemed contribution from preferred unit exchange and purchase	$ 55,700

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ 189,078	$ (393,726)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	119,070	111,574
Noncash lease expense	3,242	3,086
Amortization of debt issuance costs	6,608	6,313
Unit-based and noncash compensation	8,111	8,171
(Income) loss from equity method investees	(11,271)	337,851
Distributions from equity method investees	28,185	37,300
Gain on asset sales, net	(307)	(1,536)
Gain on early extinguishment of debt	(206,975)	0
Gain on fair value of warrants	(393)	0
Settlement of interest rate derivative	134	0
Long-lived asset impairment	13,089	60,507
Goodwill impairment	0	16,211
Changes in operating assets and liabilities:
Accounts receivable	35,352	(5,466)
Trade accounts payable	(4,063)	(96)
Accrued expenses	2,841	(10,572)
Deferred revenue, net	6,036	1,683
Ad valorem taxes payable	609	(1,525)
Accrued interest	(3,343)	7
Accrued environmental remediation, net	(1,996)	(1,152)
Other, net	14,582	(6,889)
Net cash provided by operating activities	198,589	161,741
Cash flows from investing activities:
Capital expenditures	(43,128)	(182,291)
Proceeds from asset sale (net of cash of $1,475 for the year ended December 31, 2019)	0	102,111
Distribution from equity method investment	0	7,313
Other, net	2,486	313
Net cash used in investing activities	(140,569)	(90,870)
Cash flows from financing activities:
Net cash distributions to noncontrolling interest SMLP unitholders	(6,037)	(68,874)
Series A Preferred Unit distributions	0	(28,500)
Net cash distributions to Energy Capital Partners	0	(120,730)
Borrowings under Revolving Credit Facility	249,300	369,000
Repayments on Revolving Credit Facility	(69,300)	(158,000)
Transaction costs	(4,221)	0
Repayments on SMPH Term Loan before TL Restructuring	(6,300)	(65,250)
Proceeds from issuance of Subsidiary Series A preferred units, net of issuance costs	48,710	27,392
Preferred Tender	(25,000)	0
Borrowings under ECP Loans	35,000	0
Repayment of ECP Loans	(35,000)	0
Purchase of common units in GP Buy-In Transaction	(41,778)	0
Debt issuance costs	(2,558)	(673)
Proceeds from asset sale	288	0
Other, net	(2,905)	(4,487)
Net cash used in financing activities	(79,398)	(50,122)
Net change in cash, cash equivalents and restricted cash	(21,378)	20,749
Cash, cash equivalents and restricted cash, beginning of period	36,922	16,173
Cash, cash equivalents and restricted cash, end of period	15,544	36,922
Senior Secured Term Loan Due May 2022
Cash flows from financing activities:
TL Restructuring	(26,500)	0
Double E
Cash flows from investing activities:
Investment in Double E equity method investee	(99,927)	(18,316)
Open Market Repurchases
Cash flows from financing activities:
Repurchases of 2022 and 2025 Senior Notes (Note 10)	(145,567)	0
Tender Offers
Cash flows from financing activities:
Repurchases of 2022 and 2025 Senior Notes (Note 10)	$ (47,530)	$ 0

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Statement Of Cash Flows [Abstract]
Net of cash	$ 1,475

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

1. ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

Organization. Summit Midstream Partners, LP (including its subsidiaries, collectively “SMLP” or the “Partnership”) is a Delaware limited partnership that was formed in May 2012 and began operations in October 2012. SMLP is a value-oriented limited partnership focused on developing, owning and operating midstream energy infrastructure assets that are strategically located in unconventional resource basins, primarily shale formations, in the continental United States. The Partnership’s business activities are conducted through various operating subsidiaries, each of which is owned or controlled by its wholly owned subsidiary holding company, Summit Holdings, a Delaware limited liability company. As of December 31, 2020, the Partnership indirectly owns its General Partner, and the General Partner is a wholly owned, indirect subsidiary of the Partnership. The General Partner has no assets or liabilities and holds the non-economic general partner interest in the Partnership.

GP Buy-In Transaction. On May 28, 2020, the Partnership closed the transactions contemplated by the Purchase Agreement (the “Purchase Agreement”), dated May 3, 2020, with affiliates of its then private equity sponsor, Energy Capital Partners II, LLC (“ECP”), to acquire Summit Investments. The acquisition of Summit Investments resulted in the Partnership acquiring (a) 2.3 million SMLP common units that were pledged as collateral under the SMPH Term Loan, (b) 0.7 million SMLP common units that were not pledged as collateral under the SMPH Term Loan and (c) a deferred purchase price obligation receivable owed by the Partnership. In addition, the Partnership acquired 0.4 million SMLP common units held by an affiliate of ECP. The total purchase price was $35.0 million in cash and warrants giving ECP the right to purchase up to 0.7 million SMLP common units (refer to Note 13 – Partners’ Capital and Mezzanine Capital for additional details). Pursuant to the Purchase Agreement, the Partnership retained any liabilities stemming from the release of produced water from a produced water pipeline operated by Meadowlark Midstream, a subsidiary of the Partnership, that occurred near Williston, North Dakota and was discovered on January 6, 2015. These transactions are collectively referred to as the “GP Buy-In Transaction.”

As a result of the GP Buy-In Transaction, the Partnership indirectly owns its General Partner. Following the closing of the GP Buy-In Transaction, the Partnership retired 1.1 million SMLP common units it acquired that were not pledged as collateral under the SMPH Term Loan. The 2.3 million SMLP common units that were pledged as collateral under the SMPH Term Loan were not considered outstanding with respect to voting and distributions under the Partnership Agreement until the closing of the TL Restructuring on November 17, 2020 (refer to Note 10).

Under GAAP, the GP Buy-In Transaction was deemed a transaction among entities under common control with a change in reporting entity. Although SMLP is the surviving entity for legal purposes, Summit Investments is the surviving entity for accounting purposes; therefore, the historical financial results included herein, prior to the GP Buy-In Transaction are those of Summit Investments. Prior to the GP Buy-In Transaction, Summit Investments controlled SMLP and SMLP’s financial statements were consolidated into Summit Investments.

Reverse Unit Split. On November 9, 2020, after the close of trading on the NYSE, the Partnership effected a 1-for-15 reverse unit split (the “Reverse Unit Split”) of its common units. The common units began trading on a split-adjusted basis on November 10, 2020. Pursuant to the Reverse Unit Split, common unitholders received one common unit for every 15 common units owned at the close of business on November 9, 2020. Immediately prior to the Reverse Unit Split, there were 56,624,887 common units issued and outstanding and immediately after the Reverse Unit Split, the number of issued and outstanding common units decreased to 3,774,992.

Business Operations. The Partnership provides natural gas gathering, compression, treating and processing services as well as crude oil and produced water gathering services pursuant to primarily long-term, fee-based agreements with its customers. The Partnership’s results are primarily driven by the volumes of natural gas that it gathers, compresses, treats and/or processes as well as by the volumes of crude oil and produced water that it gathers. Other than the Partnership’s investments in Double E and Ohio Gathering, all of its business activities are conducted through wholly owned operating subsidiaries

Presentation and Consolidation. The Partnership prepares its consolidated financial statements in accordance with GAAP as established by the FASB. The Partnership makes estimates and assumptions that affect the reported amounts of assets and liabilities at the balance sheet dates, including fair value measurements, the reported amounts of revenues and expenses and the

disclosure of commitments and contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates.

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

Risks and Uncertainties. The Partnership is closely monitoring the impact of the outbreak of COVID-19 on all aspects of its business, including how it has impacted and will impact its customers, employees, supply chain and distribution network. The Partnership is unable to predict the ultimate impact that COVID-19 may have on its business, future results of operations, financial position or cash flows.

Given the dynamic nature of the COVID-19 pandemic and related market conditions, the Partnership cannot reasonably estimate the period of time that these events will persist or the full extent of the impact they will have on its business. The full extent to which the Partnership’s operations may be impacted by the COVID-19 pandemic will depend largely on future developments, which are highly uncertain and cannot be accurately predicted, including changes in the severity of the pandemic, countermeasures taken by governments, businesses and individuals to slow the spread of the pandemic, and the ability of pharmaceutical companies to develop effective and safe vaccines and therapeutic drugs. Furthermore, the impacts of a potential worsening of global economic conditions and the continued disruptions to and volatility in the financial markets remain unknown.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Cash, Cash Equivalents and Restricted Cash. The Partnership considers all highly liquid investments with an original maturity of three months or less to be cash equivalents.

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

Property, Plant and Equipment. The Partnership records property, plant and equipment at historical cost of construction or fair value of the assets at acquisition. The Partnership capitalizes expenditures that extend the useful life of an asset or enhance its productivity or efficiency from its original design over the expected remaining period of use. For maintenance and repairs that do not add capacity or extend the useful life of an asset, the Partnership recognizes expenditures as an expense as incurred. The Partnership capitalizes project costs incurred during construction, including interest on funds borrowed to finance the construction of facilities, as construction in progress. Accrued capital expenditures are reflected in trade accounts payable.

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

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

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

The Partnership bases an asset’s carrying value on estimates, assumptions and judgments for useful life and salvage value. Upon sale, retirement or other disposal, the Partnership removes the carrying value of an asset and its accumulated depreciation from its balance sheet and recognizes the related gain or loss, if any.

Asset Retirement Obligations. The Partnership records a liability for asset retirement obligations only if and when a future asset retirement obligation with a determinable life is identified. For identified asset retirement obligations, the Partnership evaluates

whether the expected retirement date and related costs of retirement can be estimated. The Partnership has concluded that its gathering and processing assets have an indeterminate life because they are owned and will operate for an indeterminate period when properly maintained. Because the Partnership does not have sufficient information to reasonably estimate the amount or timing of such obligations and does not have any current plan to discontinue use of any significant assets, the Partnership did not provide for any asset retirement obligations as of December 31, 2020 or 2019.

Amortizing Intangibles. The Partnership has certain acquired gas gathering contracts that had above-market pricing structures at the acquisition date and the Partnership amortizes these favorable contracts using a straight-line method over the contract’s estimated useful life. The Partnership defines useful life as the period over which the contract is expected to contribute to the Partnership’s future cash flows. These favorable contracts have original terms ranging from 10 years to 20 years and the Partnership recognizes the amortization expense associated with these contracts in Other revenues.

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

The Partnership also has rights-of-way associated with municipal easements and easements granted within existing rights-of-way. The Partnership amortizes these intangible assets over the shorter of the contractual term of the rights-of-way or the estimated useful life of the gathering system. The contractual terms of the rights-of-way range from 20 years to 30 years and the Partnership recognizes the amortization expense associated with these rights-of-way assets in Depreciation and amortization expense.

Equity Method Investments. The Partnership accounts for investments in which it exercises significant influence using the equity method so long as it (i) does not control the investee and (ii) is not the primary beneficiary. The Partnership reflects these investments in its consolidated balance sheets under the caption titled “investment in equity method investees.”

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

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

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

Commitments and Contingencies. When required, the Partnership records accruals for loss contingencies in accordance with FASB ASC 450, Contingencies. Such determinations are subject to interpretations of current facts and circumstances, forecasts of future events and estimates of the financial impacts of such events.

Noncontrolling Interest and Mezzanine Capital. A noncontrolling interest represents the portion of a consolidated subsidiary that is owned by a third party. Amounts are adjusted by the noncontrolling interest holder’s proportionate share of the subsidiary’s earnings or losses each period and any distributions that are paid. A noncontrolling interest is reported as a

component of equity unless the noncontrolling interest is considered redeemable, in which case the noncontrolling interest is recorded between liabilities and equity (mezzanine or temporary equity) in the Partnership’s consolidated balance sheet.

Revenue Recognition. The Partnership provides gathering and/or processing services principally under contracts that contain one or more of the following arrangements described below:

•

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

•

Percent-of-proceeds arrangements. Under percent-of-proceeds arrangements, the Partnership generally purchases natural gas from producers at the wellhead, or other receipt points, gathers the wellhead natural gas through its gathering system, treats and compresses the natural gas, processes the natural gas and/or sells the natural gas to a third party for processing. The Partnership then remits to its producers an agreed-upon percentage of the actual proceeds received from sales of the residue natural gas and NGLs. Certain of these arrangements may also result in returning all or a portion of the residue natural gas and/or the NGLs to the producer, in lieu of returning sales proceeds. The margins earned are directly related to the volume of natural gas that flows through the system and the price at which the Partnership is able to sell the residue natural gas and NGLs.

For the contracts described above, the Partnership reflects its revenues in the financial statement captions described below.

Financial statement caption:		Revenue description:
Revenues:
Gathering services and related fees		• Revenue earned from fee-based gathering, compression, treating and processing services;
Natural gas, NGLs and condensate sales		• Revenue from the sale of physical natural gas purchased from customers percent-of-proceeds arrangements (Costs are presented within cost of natural gas and NGLs);
		• Revenue from sale of condensate and NGLs retained from gathering services (Costs are presented within operation and maintenance expense); and
Other revenues		• Customer reimbursements to the Partnership for costs incurred by the Partnership on customer’s behalf (Recorded on a gross basis).

Certain of the Partnership’s gathering and/or processing agreements provide for monthly or annual MVCs. Under these MVCs, customers agree to ship and/or process a minimum volume of production on its 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 the Partnership at the end of the contracted measurement period if its actual throughput volumes are less than its contractual MVC for that period. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent contracted measurement periods to the extent that such customer's throughput volumes in a subsequent contracted measurement period exceed its MVC for that contracted measurement period.

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

Unit-Based Compensation. For awards of unit-based compensation, the Partnership determines a grant date fair value and recognizes the related compensation expense in the statements of operations over the vesting period for each respective award.

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

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

New accounting standards implemented in this Annual Report.

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

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

New accounting standards not yet implemented in this Annual Report.

ASU No. 2020-06 Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815 – 40) (“ASU 2020-06”). ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. The ASU is part of the FASB’s simplification initiative, which aims to reduce unnecessary complexity in U.S. GAAP. The ASU’s amendments are effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years. The Partnership is currently evaluating the provisions of ASU 2020-06 to determine its impact on the Partnership’s consolidated financial statements and disclosures.

ASU No. 2020-04 Reference Rate Reform (“ASU 2020-04”). ASU 2020-04 provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform on financial reporting. The amendments in ASU 2020-04 are effective as of March 12, 2020 through December 31, 2022. The Partnership is currently evaluating the provisions of ASU 2020-04 to determine its impact on the Partnership’s consolidated financial statements and disclosures.

REVENUE

12 Months Ended

Dec. 31, 2020

REVENUE

3. REVENUE

The majority of the Partnership’s revenue is derived from long-term, fee-based contracts with its customers, which include original terms of up to 25 years. The Partnership recognizes revenue earned from fee-based gathering, compression, treating and processing services in gathering services and related fees. The Partnership also earns revenue in the Williston Basin and Permian

Basin reporting segments from the sale of physical natural gas purchased from its customers under certain percent-of-proceeds arrangements. Under ASC Topic 606, these gathering contracts are presented net within cost of natural gas and NGLs. The Partnership sells natural gas that it retains from certain customers in the Barnett Shale reporting segment to offset the power expenses of the electric-driven compression on the DFW Midstream system. The Partnership also sells condensate and NGLs retained from certain of its gathering services in the Piceance Basin and Permian Basin reporting segments. Revenues from the sale of natural gas and condensate are recognized in Natural gas, NGLs and condensate sales; the associated expense is included in Operation and maintenance expense. Certain customers reimburse the Partnership for costs incurred on their behalf. The Partnership records costs incurred and reimbursed by its customers on a gross basis, with the revenue component recognized in Other revenues.

The transaction price in the Partnership’s contracts is primarily based on the volume of natural gas, crude oil or produced water transferred by its 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, the Partnership does 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, the Partnership measures the transaction price at the point of sale when the volume, mix and market price of the commodities are known.

The Partnership has contracts with MVCs that are variable and constrained. Contracts with longer 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 the Partnership’s 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. The Partnership also has 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, the Partnership allocates the contract’s transaction price to each performance obligation using its best estimate of the standalone selling price of each service in the contract.

Performance obligations for gathering services are generally satisfied over time. The Partnership utilizes 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 the Partnership’s gathering and/or processing agreements provide for monthly or annual MVCs. Under these MVCs, the Partnership’s customers agree to ship and/or process a minimum volume of production on its 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 the Partnership at the end of the contracted measurement period if its actual throughput volumes are less than its contractual MVC for that period. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent contracted measurement periods to the extent that such customer's throughput volumes in a subsequent contracted measurement period exceed its MVC for that contracted measurement period.

The Partnership recognizes customer obligations under their MVCs as revenue and contract assets when (i) it is considered 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.

Services are typically billed on a monthly basis and the Partnership does not offer extended payment terms. The Partnership does not have contracts with financing components.

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

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

	2021		2022		2023		2024		2025		Thereafter

Gathering services and related fees	$	100,182	$	84,215	$	66,330	$	49,872	$	32,996	$	22,706

Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 20.

	Year ended December 31, 2020
	Gathering services and related fees		Natural gas, NGLs and condensate sales		Other revenues		Total
	(in thousands)
Reportable Segments:
Utica Shale	$	36,509	$	—	$	—	$	36,509
Williston Basin		59,239		20,018		13,438		92,695
DJ Basin		23,868		245		3,957		28,070
Permian Basin		10,091		18,857		585		29,533
Piceance Basin		106,657		2,612		4,621		113,890
Barnett Shale		40,687		7,587		6,185		54,459
Marcellus Shale		25,741		—		—		25,741
Total reportable segments		302,792		49,319		28,786		380,897
All other segments		—		—		2,576		2,576
Total	$	302,792	$	49,319	$	31,362	$	383,473

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

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

	December 31, 2020			December 31, 2019
	(In thousands)
Contract assets, January 1, 2020	$	3,902		$	8,755
Additions		18,834			18,077
Transfers out		(20,710	)		(22,930	)
Contract assets, December 31, 2020	$	2,026		$	3,902

As of December 31, 2020, receivables with customers totaled $57.5 million and contract assets totaled $2.0 million which were included in the Accounts receivable caption on the consolidated balance sheet.

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

Contract liabilities (deferred revenue) relate to the advance consideration received from customers primarily for contributions in aid of construction. The Partnership recognizes contract liabilities under these arrangements in revenue over the contract period. For the years ended December 31, 2020 and 2019, the Partnership recognized $4.0 million and $10.1 million, respectively, of gathering services and related fees which was included in the contract liability balance as of the beginning of the period. See Note 8 for additional details.

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130551-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130550-203045

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130558-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Property Plant And Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT, NET

12 Months Ended

Dec. 31, 2020

PROPERTY, PLANT, AND EQUIPMENT, NET

4. PROPERTY, PLANT AND EQUIPMENT, NET

Details on the Partnership’s property, plant and equipment follow.

	December 31, 2020			December 31, 2019
	(In thousands)
Gathering and processing systems and related equipment	$	2,213,501		$	2,182,950
Construction in progress		60,443			78,716
Land and line fill		10,440			10,137
Other		61,340			54,595
Total		2,345,724			2,326,398
Less accumulated depreciation		(528,178	)		(443,909	)
Property, plant and equipment, net	$	1,817,546		$	1,882,489

When the carrying amount of a long-lived asset is not recoverable, an impairment is recognized equal to the excess of the asset’s carrying value over its fair value, which is based on inputs that are not observable in the market, and thus represent Level 3 inputs under GAAP’s fair value hierarchy. The Partnership recognized $13.1 million and $59.4 million of impairments during the fiscal years ended December 31, 2020 and 2019, respectively. Due to the volatility of the inputs used, the Partnership cannot predict the likelihood of any future impairment. The details on significant impairments recognized during the years ended December 31, 2020 and 2019 are provided below.

Significant 2020 Impairments. The Partnership recognized a $5.1 million impairment related to the 2021 sale of compressor equipment in which the carrying value of the equipment exceeded the sale price, and a $3.6 million impairment related to the cancellation of a DJ Basin compressor station construction project due to delays in customer drilling plans.

Significant 2019 Impairments. The Partnership recognized a $34.7 million impairment resulting from the expansion of a processing plant in the DJ Basin that caused a significant reduction in the utilization of the original processing plant’s infrastructure, a $14.2 million impairment resulting from the sale of gathering system in the Piceance Basin in which the carrying value of the system exceeded the sale price, and a $9.7 million impairment of compressor equipment in the Barnett Shale.

Depreciation expense and capitalized interest for the Partnership follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Depreciation expense	$	86,263	$	78,489
Capitalized interest		3,878	$	6,974

AMORTIZING INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

AMORTIZING INTANGIBLE ASSETS

5. AMORTIZING INTANGIBLE ASSETS

Details regarding the Partnership’s intangible assets, all of which are subject to amortization, follow.

	December 31, 2020
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(16,064	)	$	8,131
Contract intangibles		278,448		(195,243	)		83,205
Rights-of-way		157,271		(49,041	)		108,230
Total intangible assets	$	459,914	$	(260,348	)	$	199,566

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

The Partnership recognized amortization expense of its favorable gas gathering contracts in Other revenues as follows:

	Year ended December 31,
	2020			2019
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(938	)	$	(1,220	)

The Partnership recognized amortization expense of its contract and right of way intangibles in costs and expenses as follows:

	Year ended December 31,
	2020		2019
	(In thousands)
Amortization expense – contract intangibles	$	25,694	$	25,587
Amortization expense – rights-of-way		6,175		6,278

The Partnership’s estimated aggregate annual amortization expected to be recognized as of December 31, 2020 for each of the five succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2021	$	28,212
2022		25,145
2023		25,091
2024		14,920
2025		14,898

GOODWILL

12 Months Ended

Dec. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

GOODWILL

6. GOODWILL

The Partnership evaluates goodwill whenever events or circumstances indicate that it is more likely than not that the fair value of a reporting unit is less than its carrying value, including goodwill. If the reporting unit’s fair value exceeds its carrying value, including goodwill, the Partnership concludes that the goodwill of the reporting unit has not been impaired and no further work is performed. If it is determined that the reporting unit’s carrying value, including goodwill, exceeds its fair value, an impairment loss is recognized in the amount of the excess of the carrying value over the fair value. The Partnership’s impairment determinations, in the context of (i) its annual impairment evaluations and (ii) other-than-annual impairment evaluations involved significant assumptions and judgments. Differing assumptions regarding any of these inputs could have a significant effect on the valuations. As such, the fair value measurements utilized within these models are classified as non-recurring Level 3 measurements in the fair value hierarchy because they are not observable from objective sources.

As of September 30, 2019, the Partnership performed its annual goodwill impairment testing for the Mountaineer Midstream reporting unit, a reporting unit included in the Marcellus Shale reportable segment, using a combination of the income and market approaches. It was determined that the fair value of the Mountaineer Midstream reporting unit did not exceed its carrying value, including goodwill. As a result, a goodwill impairment charge of $16.2 million was recorded for the year ended December 31, 2019 that reduced the goodwill balance on the Partnership’s consolidated balance sheet to zero. The Partnership did not have a transaction in 2020 that resulted in the establishment of a goodwill balance.

EQUITY METHOD INVESTMENTS

12 Months Ended

Dec. 31, 2020

Equity Method Investments And Joint Ventures [Abstract]

EQUITY METHOD INVESTMENTS

7. EQUITY METHOD INVESTMENTS

Double E. In June 2019, the Partnership formed Double E in connection with (the “Double E Project”). Effective June 26, 2019, Summit Permian Transmission, a wholly owned, indirect and consolidated subsidiary of the Partnership, and an affiliate of Double E’s foundation shipper (the “JV Partner”), executed a definitive joint venture agreement (“Double E Agreement”) to fund the capital expenditures associated with the development of the Double E Project. In connection with the Double E Agreement and the related Double E Project, the Partnership contributed total assets of approximately $23.6 million in exchange for a 70% ownership interest in Double E and the JV Partner contributed $7.3 million of cash in exchange for a 30% ownership interest in Double E. Concurrent with these contributions, and in accordance with the Double E Agreement, Double E distributed $7.3 million to the Partnership. Subsequent to the formation of Double E, the Partnership made additional cash investments to Double E of $99.9 million, which includes $2.7 million in capitalized interest, and $18.3 million, which includes $1.1 million in capitalized interest and $0.7 million in capitalized legal costs, in 2020 and 2019, respectively.

Double E is deemed to be a variable interest entity as defined in GAAP. As of the date of the Double E Agreement, Summit Permian Transmission was not deemed to be the primary beneficiary of Double E due to the JV Partner’s voting rights on significant matters. The Partnership accounts for its ownership interest in Double E as an equity method investment because it has significant influence over Double E. The Partnership’s portion of Double E’s net assets, which was $132.9 million and $34.7 million at December 31, 2020 and 2019, respectively, is reported under the caption Investment in equity method investees on the consolidated balance sheet.

For the years ended December 31, 2020 and 2019, other than the investment activity noted above, Double E did not have any results of operations given that the Double E Project is currently under development.

Ohio Gathering. The Partnership has investments in OGC and OCC that it collectively refers to as Ohio Gathering. Ohio Gathering is accounted for as an equity method investment because it has joint control with non-affiliated owners, which gives the Partnership significant influence.

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. The Partnership made its initial investment in Ohio Gathering in 2014 and owned 38.2% and 38.5% of Ohio Gathering at December 31, 2020 and 2019, respectively.

In December 2019, the Partnership identified certain triggering events which indicated that its equity method investment in Ohio Gathering could be impaired. In accordance with ASC Topic 323, an equity method impairment analysis was performed and determined the equity method impairment charge to be recorded on its consolidated financial statements resulting from an

other-than-temporary impairment. As a result of the analysis, an impairment charge of $329.7 million was recorded in 2019 in Loss from equity method investments on the accompanying consolidated statements of operations.

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

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

A reconciliation of the difference between the carrying amount of the Partnership’s interest in Ohio Gathering and the Partnership’s underlying investment in Ohio Gathering, per Ohio Gathering’s books and records, is shown below.

	2020		2019
	(In thousands)
Investment in Ohio Gathering, December 31,	$	259,888	$	275,000
December cash distributions		2,748		2,700
Impairment loss⁽¹⁾		—		232,521
Basis difference		216,591		—
Investment in Ohio Gathering (Books and records), November 30,	$	479,227	$	510,221

⁽¹⁾ Amount is comprised of (i) a $329.7 million impairment of the Partnership’s equity method investment in Ohio Gathering; (ii) the write-off of the Partnership’s basis difference of $103.5 million in Ohio Gathering as a result of the impairment in the Partnership’s equity method investment in Ohio Gathering; and (iii) a $6.3 million impairment of long-lived assets in OCC.

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

	November 30, 2020				November 30, 2019
	OGC		OCC		OGC		OCC
	(In thousands)
Current assets	$	32,404	$	4,902	$	41,972	$	2,187
Noncurrent assets		1,240,090		290		1,281,171		28,323
Total assets	$	1,272,494	$	5,192	$	1,323,143	$	30,510

Current liabilities	$	8,424	$	2,982	$	21,798	$	4,016
Noncurrent liabilities		8,441		5,146		4,113		6,683
Total liabilities	$	16,865	$	8,128	$	25,911	$	10,699

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

	Twelve months ended November 30, 2020					Twelve months ended November 30, 2019
	OGC		OCC			OGC		OCC
	(In thousands)
Total revenues	$	114,524	$	12,931		$	142,138	$	8,601
Total operating expenses		103,020		38,502			108,234		38,815
Net income (loss)		11,496		(25,571	)		33,897		(30,214	)

DEFERRED REVENUE

12 Months Ended

Dec. 31, 2020

Liability Management Transactions [Abstract]

DEFERRED REVENUE

8. DEFERRED REVENUE

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

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

•

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

•

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

•

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

A rollforward of current deferred revenue follows.

	Total
	(In thousands)
Current deferred revenue, January 1, 2020	$	13,493
Additions		2,731
Less: revenue recognized		6,236
Current deferred revenue, December 31, 2020	$	9,988

A rollforward of noncurrent deferred revenue follows.

	Total
	(In thousands)
Noncurrent deferred revenue, January 1, 2020	$	38,709
Additions		19,384
Less: reclassification to current deferred revenue		9,843
Noncurrent deferred revenue, December 31, 2020	$	48,250

DEBT

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

DEBT

9. DEBT

Debt for the Partnership at December 31, 2020 and 2019 follows.

	December 31, 2020			December 31, 2019
	(In thousands)
Revolving Credit Facility: Summit Holdings' variable rate senior secured Revolving Credit Facility (2.90% at December 31, 2020 and 4.55% at December 31, 2019) due May 2022	$	857,000		$	677,000
ECP Loans: Summit Holdings' 8.00% senior secured term loan obtained in May 2020 and fully repaid in August 2020		—			—
2022 Senior Notes: Summit Holdings' 5.5% senior unsecured notes due August 2022		234,047			300,000
Less: unamortized debt issuance costs (1)		(859	)		(1,686	)
2025 Senior Notes: Summit Holdings' 5.75% senior unsecured notes due April 2025		259,463			500,000
Less: unamortized debt issuance costs (1)		(2,325	)		(5,015	)
SMPH Term Loan: SMP Holdings' variable rate senior secured term loan (7.80% at December 31, 2019) due May 2022 and extinguished in November 2020		—			161,500
Less: unamortized debt issuance costs (1)		—			(3,974	)
Total debt		1,347,326			1,627,825
Less: current portion		—			(5,546	)
Total long-term debt	$	1,347,326		$	1,622,279

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

The aggregate amount of Partnership’s debt maturing during each of the years after December 31, 2020 are as follows (in thousands):

2021	$	—
2022		1,091,047
2023		—
2024		—
2025		259,463
Thereafter		—
Total long-term debt	$	1,350,510

Revolving Credit Facility. The Partnership’s subsidiary, Summit Holdings, has a senior secured revolving credit facility (the “Revolving Credit Facility”) which allows for revolving loans, letters of credit and swingline loans. SMLP and the Guarantor Subsidiaries fully and unconditionally and jointly and severally guarantee, and pledge substantially all of their assets in support of the indebtedness outstanding under the Revolving Credit Facility. At December 31, 2020, the Revolving Credit Facility has a $1.1 billion borrowing capacity and matures in May 2022.

On December 18, 2020, Summit Holdings entered into the Fourth Amendment to the Third Amended and Restated Credit Agreement which amended the Revolving Credit Facility to: (i) reduce the commitments from $1.25 billion to $1.1 billion; (ii) eliminate the $250.0 million accordion feature; (iii) add a basket for the potential issuance of up to $400.0 million of junior lien indebtedness; (iv) revise restrictions on the Partnership’s ability to use operating cash flow to repurchase junior debt and equity securities; (v) increase the total leverage covenant from 5.50x to 5.75x at all times going forward; (vi) replace the 3.75x senior secured leverage covenant with a new 3.50x first lien leverage covenant; (vii) add a new pricing tier of L + 325 bps if the total leverage ratio is greater than 5.00x; and (viii) restrict the Partnership’s ability to resume distributions on preferred and common units, subject to achieving certain financial and liquidity thresholds.

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 2.25% or the adjusted Eurodollar rate (as defined in the credit agreement) plus an applicable margin ranging from 1.75% to 3.25%, with the commitment fee ranging from 0.30% to 0.50% in each case based on the Partnership’s relative leverage at the time of determination. At December 31, 2020, the applicable margin under LIBOR borrowings was 2.75%, the interest rate was 2.9% and the unused portion of the

Revolving Credit Facility totaled $238.9 million, subject to a commitment fee of 0.50%, after giving effect to the issuance thereunder of a $4.1 million outstanding but undrawn irrevocable standby letter of credit. Based on covenant limits, the available borrowing capacity under the Revolving Credit Facility as of December 31, 2020 was approximately $105 million.

At December 31, 2020, the Revolving Credit Facility is secured by the membership interests of Summit Holdings and the membership interests of the Guarantor Subsidiaries of Summit Holdings and by substantially all of the assets of Summit Holdings and its Guarantor Subsidiaries (subject to exclusions set forth in the credit agreement). The credit agreement contains affirmative and negative covenants customary for credit facilities of its size and nature that, among other things, limit or restrict the ability (i) to incur additional debt; (ii) to make investments; (iii) to engage in certain mergers, consolidations, acquisitions or sales of assets; (iv) to enter into swap agreements and power purchase agreements; (v) to enter into leases that would cumulatively obligate payments in excess of $50.0 million over any 12 -month period; and (vi) of Summit Holdings to make distributions, with certain exceptions, including the distribution of Available Cash (as defined in the SMLP Partnership Agreement) if no default or event of default then exists or would result therefrom and Summit Holdings is in pro forma compliance with its financial covenants. In addition, the Revolving Credit Facility requires Summit Holdings to maintain (i) a ratio of consolidated trailing 12 -month earnings before interest, income taxes, depreciation and amortization ("EBITDA") to net interest expense of not less than 2.5 to 1.0 as defined in the credit agreement, (ii) a ratio of total net indebtedness to consolidated trailing 12 -month EBITDA of not more than 5.75 to 1.00 and, (iii) a ratio of first lien net indebtedness to consolidated trailing 12 -month EBITDA of not more than 3.75 to 1.00. As of December 31, 2020, the Partnership was in compliance with the Revolving Credit Facility's financial covenants and there were no defaults or events of default during the year ended December 31, 2020.

As of December 31, 2020, the Partnership had $7.4 million of debt issuance costs attributable to its Revolving Credit Facility and related amendments, which are included in Other noncurrent assets on the consolidated balance sheet.

ECP Loans. On May 28, 2020, in connection with the closing of the GP Buy-In Transaction, Summit Holdings, entered into (i) a Term Loan Credit Agreement (the “ECP NewCo Term Loan Credit Agreement”), with SMP TopCo, LLC, a Delaware limited liability company and affiliate of ECP (“ECP NewCo”), as lender and administrative agent, and Mizuho Bank (USA) (“Mizuho”), as collateral agent, in a principal amount of $28.2 million (the “ECP NewCo Loan”), and (ii) a Term Loan Credit Agreement (the “ECP Holdings Term Loan Credit Agreement” and together with the ECP NewCo Term Loan Credit Agreement, the “ECP Term Loan Credit Agreements”), with ECP Holdings, as lender, and ECP NewCo, as administrative agent and Mizuho, as collateral agent, in a principal amount of $6.8 million (the “ECP Holdings Loan” and together with the ECP NewCo Loan, the “ECP Loans”). The ECP Loans were set to mature on March 31, 2021 and bore interest at a fixed rate of 8.00% per annum, with the interest payment due at maturity of the ECP Loans. With borrowings under the Partnership’s Revolving Credit Facility, the Partnership fully repaid all amounts outstanding under the ECP Loans ($35 million of principal and $0.6 million of accrued interest) on August 7, 2020.

2022 Senior Notes. In July 2014, the Co-Issuers co-issued the 2022 Senior Notes. The Partnership pays interest on the 2022 Senior Notes semi-annually in cash in arrears on February 15 and August 15 of each year. The 2022 Senior Notes are senior, unsecured obligations and rank equally in right of payment with all of our existing and future senior obligations. The 2022 Senior Notes are effectively subordinated in right of payment to all secured indebtedness, to the extent of the collateral securing such indebtedness. The Co-Issuers may redeem all or part of the 2022 Senior Notes at a redemption price of 100.000%, plus accrued and unpaid interest, if any. Debt issuance costs of $5.1 million are being amortized over the life of the 2022 Senior Notes. As of and during the year ended December 31, 2020, we were in compliance with the financial covenants governing its 2022 Senior Notes.

2025 Senior Notes. In February 2017, the Co-Issuers co-issued the 2025 Senior Notes. The Partnership pays interest on the 2025 Senior Notes semi-annually in cash in arrears on April 15 and October 15 of each year. The 2025 Senior Notes are senior, unsecured obligations and rank equally in right of payment with all of the Partnership’s existing and future senior obligations. The 2025 Senior Notes are effectively subordinated in right of payment to all of the Partnership’s secured indebtedness, to the extent of the collateral securing such indebtedness.

The Co-Issuers have the right to redeem all or part of the 2025 Senior Notes at a redemption price of 104.313%. On and after April 15, 2021, the Co-Issuers may redeem all or part of the 2025 Senior Notes at a redemption price of 102.875% (with the redemption price declining ratably each year to 100.000% on April 15, 2023), plus accrued and unpaid interest, if any, to, but not including, the redemption date. Debt issuance costs of $7.7 million are being amortized over the life of the 2025 Senior Notes.

As of and during the year ended December 31, 2020, that Partnership was in compliance with the financial covenants governing its 2025 Senior Notes.

SMPH Term Loan and TL Restructuring. Until November 17, 2020, a subsidiary of the Partnership, SMP Holdings, had a senior secured term loan facility with $155.2 million of principal outstanding and a maturity date of May 15, 2022. Borrowings under the SMPH Term Loan bore interest at LIBOR plus 6.00% or ABR plus 5.00%, as defined in the SMPH Term Loan, and were secured by the following collateral: (i) a perfected first-priority lien on, and pledge of (a) all of the capital stock issued by SMP Holdings, (b) 2.3 million SMLP units owned by SMP Holdings, (c) all of the equity interests owned by SMP Holdings in the General Partner, and (ii) substantially all other personal property of SMP Holdings.

On September 29, 2020, SMP Holdings, Summit Investments and, for limited purposes, the Partnership, entered into the TL Restructuring. At the closing of the TL Restructuring on November 17, 2020, the Term Loan Agent executed a Strict Foreclosure on behalf of the Term Loan Lenders on the 2,306,972 common units held by SMP Holdings and pledged as collateral under the SMPH Term Loan, which was then distributed to all SMPH Term Loan Lenders on a pro rata basis. In addition to the Strict Foreclosure, SMP Holdings paid to each of the SMPH Term Loan Lenders its pro rata share of $26.5 million in cash that the Partnership paid to SMP Holdings to fully satisfy its obligation with respect to the deferred purchased price obligation.

As of December 31, 2020, the SMPH Term Loan is fully satisfied and no longer exists.

LIABILITY MANAGEMENT TRANSACTIONS

12 Months Ended

Dec. 31, 2020

Liability Management Transactions

10. LIABILITY MANAGEMENT TRANSACTIONS

During the year ended December 31, 2020, the Partnership and its subsidiaries completed several liability management transactions, described below, that resulted in the early extinguishment of an aggregate $306.5 million face value of the Partnership’s indebtedness.

Open Market Repurchases. During the year ended December 31, 2020, the Partnership made a number of open market repurchases of the 2022 Senior Notes and 2025 Senior Notes that resulted in the extinguishment of $32.4 million of face value of the 2022 Senior Notes and $201.8 million of face value of the 2025 Senior Notes (the “Open Market Repurchases”). Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 Senior Notes and 2025 Senior Notes, plus accrued interest totaled $150.3 million and the Partnership recognized a $86.4 million gain on the early extinguishment of debt during the year ended December 31, 2020.

Debt Tender Offers. In September 2020, the Co-Issuers completed the Debt Tender Offers to purchase a portion of the 2022 Senior Notes and 2025 Senior Notes. Upon concluding the Debt Tender Offers, the Co-Issuers repurchased $33.5 million principal amount of the 2022 Senior Notes and $38.7 million principal amount of the 2025 Senior Notes. Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 and 2025 Senior Notes, plus accrued interest, totaled $48.7 million, and the Partnership recognized a $23.3 million gain on the early extinguishment of debt during the year ended December 31, 2020.

SMPH Term Loan Restructuring. On November 17, 2020, the Partnership completed the TL Restructuring and recognized a gain of $94.0 million equal to the difference between the face value of the cancelled SMPH Term Loan and the fair value of the total consideration transferred, including unamortized debt issuance costs, and certain direct transaction costs related to the restructuring. The transaction was accounted for under ASC Topic 470-60 “Troubled Debt Restructuring with Debtors” and had a total impact of $26.15 per share.

Summary of gain on extinguishment of debt. The Partnership recognized a $203.1 million gain on extinguishment of debt during the year ended December 31, 2020, the components of which are summarized in the table below.

	ECP Loan Repayment			Open Market Repurchases						Tender Offers						TL Restructuring			Total
				2022			2025			2022			2025
(in thousands)				Senior Notes			Senior Notes			Senior Notes			Senior Notes
Gain on Repurchases of Senior Notes and TL Restructuring	$	—		$	11,554		$	76,789		$	9,223		$	15,479		$	99,175		$	212,220
Debt issue costs		(361	)		(143	)		(1,541	)		(125	)		(351	)		(2,724	)		(5,245	)
Transaction costs		(249	)		(105	)		(105	)		(467	)		(467	)		(2,520	)		(3,913	)
Gain (loss) on debt extinguishment	$	(610	)	$	11,306		$	75,143		$	8,631		$	14,661		$	93,931		$	203,062

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

11. COMMITMENTS AND CONTINGENCIES

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

In 2015, the Partnership learned of the rupture of a four-inch produced water gathering pipeline on the Meadowlark Midstream system near Williston, North Dakota (“Meadowlark Rupture”). The Meadowlark Rupture, 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. The pollution liability policy was exhausted in 2015. Prior to the GP Buy-In Transaction, Summit Investments and SMP Holdings indemnified the Partnership for certain obligations and liabilities related to the incident. As a result of the GP Buy-In Transaction, the Partnership is no longer indemnified for these obligations.

A rollforward of the Partnership’s undiscounted accrued environmental remediation liabilities related to the Meadowlark Rupture follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2019	$	5,636
Payments made		(2,284	)
Additional accruals		1,299
Accrued environmental remediation, December 31, 2019	$	4,651
Payments made		(1,722	)
Accrued environmental remediation, December 31, 2020	$	2,929

As of December 31, 2020, the Partnership has 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 expected to be incurred subsequent to December 31, 2021. Each of these amounts represent the Partnership’s best estimate for costs expected to be incurred. Neither of these amounts have been discounted to its present value.

Beginning in 2015, the U.S. Department of Justice (“DOJ”) issued grand jury subpoenas to Summit Investments, the Partnership, our General Partner and Meadowlark Midstream requesting certain materials related to the Meadowlark Rupture. On June 19, 2015, Meadowlark Midstream and Summit Investments received a complaint from the North Dakota Industrial Commission seeking approximately $2.5 million in fines and other fees related to the incident. This matter is also under investigation by the U.S. Environmental Protection Agency, the North Dakota Office of the Attorney General, the North Dakota Department of Environmental Quality, and the North Dakota Game and Fish Department. The government’s investigation is still ongoing. During this time, the Partnership has entered ‎into tolling agreements with both the DOJ and the North Dakota attorney general, which ‎were most recently extended to May 7, 2021. There can be no assurance that these tolling agreements will be extended. Discussions with the DOJ and other agencies regarding a resolution of this matter are ongoing. Liability for this incident could arise under civil and misdemeanor and felony criminal statutes, including the Clean Water Act. In accordance with GAAP, the Partnership has accrued a $17.0 million loss contingency for this matter as of December 31, 2020. While the Partnership believes a loss for claims and/or actions arising from the Meadowlark Rupture, whether in a negotiated settlement or as a result of litigation, is probable, due to the complexity of resolving the numerous issues surrounding this matter, at this time we cannot reasonably predict whether any actual loss, if incurred, would be materially higher or lower than the accrued amount.

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.

FINANCIAL INSTRUMENTS

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

FINANCIAL INSTRUMENTS

12. FINANCIAL INSTRUMENTS

Concentrations of Credit Risk. Financial instruments that potentially subject the Partnership to concentrations of credit risk consist of cash and cash equivalents, restricted cash and accounts receivable. The Partnership maintains its cash and cash equivalents and restricted cash in bank deposit accounts that frequently exceed federally insured limits. The Partnership has not experienced any losses in such accounts and does not believe it is exposed to any significant risk.

Accounts receivable primarily comprise amounts due for the gathering, compression, treating and processing services the Partnership provides to its customers and also the sale of natural gas liquids resulting from its processing services. This industry concentration has the potential to impact its overall exposure to credit risk, either positively or negatively, in that the Partnerships customers may be similarly affected by changes in economic, industry or other conditions. The Partnership monitors the creditworthiness of its counterparties and can require letters of credit or other forms of credit assurance for receivables from counterparties that are judged to have substandard credit, unless the credit risk can otherwise be mitigated. The Partnerships top five customers or counterparties accounted for 51% of its total accounts receivable at December 31, 2020, compared to 46% as of December 31, 2019.

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

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

	December 31, 2020				December 31, 2019
	Carrying Value, Net		Estimated fair value (Level 2)		Carrying Value, Net		Estimated fair value (Level 2)
	(in thousands)
2022 Senior Notes	$	233,188	$	215,713	$	298,314	$	266,750
2025 Senior Notes		257,138		168,002		494,985		382,708

The carrying value on the balance sheet of the Revolving Credit Facility is its fair value due to its floating interest rate. The fair value for the Senior Notes is based on an average of nonbinding broker quotes as of December 31, 2020 and 2019. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the Senior Notes.

PARTNERS' CAPITAL AND MEZZANINE CAPITAL

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 AND MEZZANINE CAPITAL

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

13. PARTNERS' CAPITAL AND MEZZANINE CAPITAL

Noncontrolling Interest. In March 2019, and prior to the GP Buy-In Transaction, a subsidiary of Summit Investments cancelled its incentive distribution rights agreement with SMLP and converted its 2% economic general partner interest to a non-economic general partner interest in exchange for 0.6 million SMLP common units. This exchange is reflected in the Consolidated Statements of Partners’ Capital as a reduction to noncontrolling interest and an increase to Partners’ Capital.

Common Units. A rollforward of the number of common limited partner units follows for the period from December 31, 2018 to December 31, 2020.

	Common Units⁽²⁾
Units, December 31, 2018		3,021,258
2019 activity		—
Units, December 31, 2019		3,021,258
GP Buy-In Transaction⁽¹⁾		(132,687	)
Common units issued for SMLP LTIP, net		95,987
TL Restructuring (Note 9)		2,306,972
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes		817,845
Other		717
Units, December 31, 2020		6,110,092

⁽¹⁾ The purchase price for the SMLP common units reflected in the consolidated statement of partners’ capital for the year ended December 31, 2020 is comprised of the (i) the $35.0 million cash payment to ECP, (ii) the $2.3 million fair value for the issuance of 0.7 million warrants, and (iii) $6.8 million of advisory fees and other direct costs related to closing the GP Buy-In Transaction.

⁽²⁾ As adjusted for reverse unit split.

Series A Preferred Units. In November 2017, the Partnership 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. The Partnership used the net proceeds of $293.2 million (after deducting underwriting discounts and offering expenses) to repay outstanding borrowings under the Revolving Credit Facility.

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

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

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

In connection with the GP Buy-In Transaction, the Partnership suspended its distributions to be paid to holders of its Series A Preferred Units, commencing with respect to the quarter ending March 31, 2020.

A rollforward of the number of Series A Preferred Units follows for the period from December 31, 2018 to December 31, 2020.

	Series A Preferred Units
Series A Preferred Units, December 31, 2018		300,000
2019 activity		—
Series A Preferred Units, December 31, 2019		300,000
Series A Preferred Unit Exchange Offer		(62,816	)
Series A Preferred Unit Tender		(75,075	)
Series A Preferred Units, December 31, 2020		162,109

Series A Preferred Unit Exchange Offer. In July 2020, the Partnership completed an offer to exchange its Series A Preferred Units for newly issued common units, whereby it issued 837,547 SMLP common units in exchange for 62,816 Series A Preferred Units.

Series A Preferred Tender Offer. In December 2020, the Partnership completed a cash tender offer for its Series A Preferred Units whereby it accepted 75,075 Series A Preferred Units for a purchase price of $333.00 per Series A Preferred Unit and an aggregate purchase price of $25.0 million.

Subsidiary Series A Preferred Units. The Partnership has Subsidiary Series A Preferred Units that ranks senior to each other class or series of limited partner interests or other equity securities in Permian Holdco that may be established in the future that expressly ranks junior to the Subsidiary Series A Preferred Units as to the payment of distributions and amounts payable upon a liquidation event (the “Junior Securities”). The Subsidiary Series A Preferred Units rank equal in all respects with each class or

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

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

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

In 2020, the Partnership issued 55,251 Subsidiary Series A Preferred Units at a price of $1,000 per unit for net proceeds of $48.7 million (after deducting underwriting discounts and offering expenses). All proceeds were used to fund capital expenses associated with the Double E Project.
In 2019, the Partnership issued 30,000 Subsidiary Series A Preferred Units representing limited partner interests in Permian Holdco at a price of $1,000 per unit. The net proceeds of $27.4 million (after deducting underwriting discounts and offering expenses) were used to fund capital expenses associated with the Double E Project.

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

These Subsidiary Series A Preferred Units are considered redeemable securities under GAAP due to the existence of certain redemption provisions that are outside of the Partnership’s control. Therefore, the securities are classified as temporary equity in the mezzanine section of the consolidated balance sheets.

The Partnership records its Subsidiary Series A Preferred Units at fair value upon issuance, net of issuance costs, and subsequently records an effective interest method accretion amount each reporting period to accrete the carrying value to a most probable redemption value that is based on a predetermined internal rate of return measure. The Partnership also elected to make payment-in-kind (“PIK”) distributions to holders of the Subsidiary Series A Preferred Units during the year ended December 31, 2020 and these PIK distributions increase the liquidation preference on each Subsidiary Series A Preferred Unit. Ultimately, Net Income (Loss) Attributable to common limited partners includes adjustments for PIK distributions and redemption accretion.

If the Subsidiary Series A Preferred Units were redeemed on December 31, 2020, the redemption amount would be $106.6 million, when considering the applicable multiple of invested capital metric and make-whole amount provisions contained in the Subsidiary Series A Preferred Unit agreement. The following table shows the change in the Partnership’s Subsidiary Series A Preferred Unit balance during the year ended December 31, 2020:

	December 31, 2020
	(in thousands)
Balance at December 31, 2019	$	27,450
New issuances		50,000
PIK distributions		5,251
Issuance costs		(1,290	)
Redemption accretion		8,247
Balance at December 31, 2020⁽¹⁾	$	89,658

⁽¹⁾ Amount is net of $3.9 million of issuance costs at December 31, 2020.

Warrants. On May 28, 2020 and in connection with the GP Buy-In Transaction, the Partnership issued (i) a warrant to purchase up to 0.5 million SMLP common units to ECP NewCo (the “ECP NewCo Warrant”) and (ii) a warrant to purchase up to 0.1 million SMLP common units to ECP Holdings (the “ECP Holdings Warrant” and together with the ECP NewCo Warrant, the “ECP Warrants”). The exercise price under the ECP Warrants is $15.35 per SMLP common unit and the Partnership may issue a maximum of 0.7 million SMLP common units under the ECP Warrants.

Upon exercise of the ECP Warrants, each of ECP NewCo and ECP Holdings may receive, at its election: (i) a number of SMLP common units equal to the number of SMLP common units for which the ECP Warrants are being exercised, if exercising the ECP Warrants by cash payment of the exercise price; (ii) a number of SMLP common units equal to the product of the number of common units being exercised multiplied by (a) the difference between the average of the daily volume-weighted average price (“VWAP”) of the SMLP common units on the New York Stock Exchange (the “NYSE”) on each of the three trading days prior to the delivery of the notice of exercise (the “VWAP Average”) and the exercise price (the “VWAP Difference”), divided by (b) the VWAP Average; and/or (iii) an amount in cash, to the extent that the Partnership’s leverage ratio would be at least 0.5x less than the maximum applicable ratio set forth in the Revolving Credit Facility, equal to the product of (a) the number of SMLP common units exercised and (b) the VWAP Difference, subject to certain adjustments under the ECP Warrants.

The ECP Warrants are subject to standard anti-dilution adjustments for stock dividends, stock splits (including reverse splits) and recapitalizations and are exercisable at any time on or before May 28, 2023. Upon exercise of the ECP Warrants, the proceeds to the holders of the ECP Warrants, whether in the form of cash or common units, will be capped at $30.00 per SMLP common unit above the exercise price.

At issuance the ECP Warrants were valued at $2.3 million using a Black-Scholes model and accounted for as a liability instrument. At December 31, 2020, the ECP Warrants were valued at $1.9 million.

Cash Distribution Policy. In connection with the GP Buy-In Transaction, the Partnership suspended its cash distributions to holders of its common units, commencing with respect to the quarter ending March 31, 2020. Upon the resumption of distributions, the Partnership Agreement requires that it distribute all available cash, subject to reserves established by its General Partner, within 45 days after the end of each quarter to unitholders of record on the applicable record date. The amount of distributions paid under this policy is subject to fluctuations based on the amount of cash the Partnership generates from its business and the decision to make any distribution is determined by the General Partner, taking into consideration the terms of the Partnership Agreement.

Cash Distributions Paid and Declared. Prior to the GP Buy-In Transaction, SMLP paid the following per-unit cash distributions to its unitholders during the years ended December 31:

	Year ended December 31,
	2020		2019
Per-unit distributions to unitholders	$	0.125	$	1.4375

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

EARNINGS PER UNIT

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

EARNINGS PER UNIT

14. EARNINGS PER UNIT

The following table details the components of EPU.

	Year ended December 31,
	2020		2019
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net income (loss) among limited partner interests:
Net income (loss) attributable to limited partners	$	192,352	$	(184,451	)
Less:
Net income attributable to Series A Preferred Units		26,529		28,500
Net income attributable to Subsidiary Series A Preferred Units		13,498		58
Add:
Deemed capital contribution from Series A Preferred Unit Exchange Offer		54,945		—
Deemed capital contribution from Series A Preferred Tender Offer		55,724
Net income (loss) attributable to common limited partners	$	262,994	$	(213,009	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic⁽¹⁾		3,592		3,021
Effect of nonvested phantom units		102		—
Weighted-average common units outstanding – diluted		3,694		3,021

Net Income (Loss) per limited partner unit:
Common unit – basic	$	73.22	$	(70.50	)
Common unit – diluted	$	71.19	$	(70.50	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		240		12

⁽¹⁾

^{As a result of the GP Buy-In Transaction, our historical results are those of Summit Investments. The number of common units of 3.0 million as of December 31, 2019 represents those of Summit Investments and has been used for the earnings per unit calculation presented herein.}

SUPPLEMENTAL CASH FLOW INFORMATION

12 Months Ended

Dec. 31, 2020

Supplemental Cash Flow Elements [Abstract]

SUPPLEMENTAL CASH FLOW INFORMATION

15. SUPPLEMENTAL CASH FLOW INFORMATION

	Year ended December 31,
	2020		2019
	(In thousands)
Supplemental cash flow information:
Cash interest paid	$	79,450	$	92,536
Less capitalized interest		3,878		6,974
Interest paid (net of capitalized interest)	$	75,572	$	85,562

Cash paid for taxes	$	190	$	150

Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	$	6,154	$	19,846
Warrant issuance for GP Buy-In Transaction		2,300		—
Asset contribution to an equity method investment		—		23,643
Right-of-use assets relating to ASC Topic 842		3,685		5,448
Fair value of SMLP equity for TL Restructuring		30,521		—
Accretion of Subsidiary Series A Preferred Units		8,247		—

UNIT-BASED AND NONCASH COMPENSATION

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

UNIT-BASED AND NONCASH COMPENSATION

16. UNIT-BASED AND NONCASH COMPENSATION

SMLP Long-Term Incentive Plan. The Partnership’s Long-Term Incentive Plan (“SMLP LTIP”) provides for equity awards to eligible officers, employees, consultants and directors of the Partnership, thereby linking the recipients' compensation directly to SMLP’s performance. The SMLP LTIP provides for the granting, from time to time, of unit-based awards, including common

units, restricted units, phantom units, unit options, unit appreciation rights, distribution equivalent rights, profits interest units and other unit-based awards. Grants are made at the discretion of the Board of Directors or Compensation Committee. A total of 1.0 million common units was reserved for issuance pursuant to and in accordance with the SMLP LTIP. As of December 31, 2020, approximately 0.4 million common units remained available for future issuance.

The following table presents phantom unit activity for the periods presented:

	Units			Weighted-average grant date fair value
Nonvested phantom units, December 31, 2018		57,608		$	256.65
Phantom units granted		127,540			97.20
Phantom units vested		(40,174	)		251.70
Phantom units forfeited		(4,574	)		193.05
Nonvested phantom units, December 31, 2019		140,400			115.35
Phantom units granted		345,997			9.20
Phantom units vested		(193,349	)		54.07
Phantom units forfeited		(1,357	)		119.24
Nonvested phantom units, December 31, 2020		291,691		$	26.57

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

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

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

	Year ended December 31,
	2020		2019
	(In thousands)
Intrinsic value of vested LTIP awards	$	2,602	$	5,940

As of December 31, 2020, the unrecognized unit-based compensation related to the SMLP LTIP was $3.4 million. Incremental unit-based compensation will be recorded over the remaining weighted-average vesting period of approximately 1.4 years.

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

	Year ended December 31,
	2020		2019
	(In thousands)
SMLP LTIP unit-based compensation	$	8,111	$	8,171

LEASES

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

LEASES

17. LEASES

Leases. The Partnership leases certain office space and equipment under operating leases. The Partnership leases office space for terms of between 3 and 10 years. Office space leases limit exposure to risks related to ownership, such as fluctuations in real estate prices. The Partnership leases equipment primarily to support its operations in response to the needs of its gathering systems for terms of between 3 and 4 years. The Partnership also leases vehicles under finance leases to support its operations in response to the needs of its gathering systems for a term of 3 years.

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

In accordance with the provisions in the Revolving Credit Facility, the Partnership’s aggregate finance lease obligations cannot exceed $50.0 million in any period of twelve consecutive calendar months during the life of such leases.

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

The rate implicit in the lease contracts are not readily determinable. In determining the discount rate used in for lease liabilities, the Partnership analyzed certain factors in its incremental borrowing rate, including collateral assumptions and the term used. The incremental borrowing rate on the Revolving Credit Facility was 2.90% at December 31, 2020, which reflects the fixed rate at which the Partnership could borrow a similar amount, for a similar term and with similar collateral as in the lease contracts at the commencement date.

In connection with the adoption of Topic 842, the Partnership elected the package of practical expedients which permits them not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company also elected the practical expedient to not separate the nonlease components from the associated lease components for all classes of underlying assets, as well as the short-term lease recognition exemption.

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

	December 31, 2020		December 31, 2019
	(In thousands)

ROU assets
Operating	$	3,736	$	3,580
Finance		1,748		3,159
	$	5,484	$	6,739
Lease liabilities, current
Operating	$	2,298	$	1,221
Finance		618		1,246
	$	2,916	$	2,467
Lease liabilities, noncurrent
Operating	$	3,182	$	2,513
Finance		154		676
	$	3,336	$	3,189

Lease cost and Other information follow:

	Year ended December 31,
	2020		2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	1,274	$	1,559
Interest on lease liabilities (included in interest expense)		52		102
Operating lease cost (included in general and administrative expense)		2,644		3,345
	$	3,970	$	5,006

	Year ended December 31,
	2020			2019
	(In thousands)
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	1,472		$	3,396
Operating cash outflows from finance leases		52			102
Financing cash outflows from finance leases		1,150			1,873
ROU assets obtained in exchange for new operating lease liabilities		3,552			1,218
ROU assets obtained in exchange for new finance lease liabilities		133			1,350
Weighted-average remaining lease term (years) - operating leases		4.9			5.8
Weighted-average remaining lease term (years) - finance leases		1.4			2.0
Weighted-average discount rate - operating leases		5	%		5	%
Weighted-average discount rate - finance leases		4	%		4	%

The Partnership recognizes total lease expense incurred or allocated to us in general and administrative expenses. Lease expense related to operating leases, including lease expense incurred on the Partnership’s behalf and allocated to us, was as follows:

	Year ended December 31,
	2020		2019
	(In thousands)
Lease expense	$	3,436	$	4,038

Future minimum lease payments due under noncancelable leases at December 31, 2020, were as follows:

	December 31, 2020
	(In thousands)
	Operating		Finance
2021	$	1,750	$	655
2022		1,308		126
2023		854		42
2024		573		—
2025		464		—
2026		156		—
Thereafter		579		—
Total future minimum lease payments	$	5,684	$	823

DISPOSITIONS

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

DISPOSITIONS

18. DISPOSITIONS

In 2019, the Partnership completed two divestitures described in further detail below.

Red Rock Gathering Asset Disposition. In December 2019, the Partnership completed the sale of certain assets contained in its Piceance Basin reportable segment for a cash purchase price of $12.0 million. Prior to the sale, the Partnership recorded an impairment charge of $14.2 million based on the expected consideration and the carrying value for the disposed assets. The financial contribution of these assets in 2019 (a component of the Piceance Basin reportable segment) are included in the Partnership’s consolidated financial statements and footnotes for the period from January 1, 2019 through December 1, 2019.

Tioga Midstream Disposition. In March 2019, the Partnership closed on the sale of certain assets contained in the Williston Basin reportable segment for a cash purchase price of $90.0 million. Upon closing the sale in March 2019, the Partnership recorded a gain on sale of $0.9 million based on the difference between the consideration received and the carrying value for disposed assets. The gain is included in the Gain on asset sales, net caption on the consolidated statement of operations. The financial contribution of these assets in 2019 (a component of the Williston Basin reportable segment) are included in the Partnership’s consolidated financial statements and footnotes for the period from January 1, 2019 through March 22, 2019.

RESTRUCTURING

12 Months Ended

Dec. 31, 2020

Restructuring And Related Activities [Abstract]

RESTRUCTURING

19. RESTRUCTURING

2020 Restructuring Activities. In 2020, management approved and initiated a plan to restructure its operations (“2020 Restructuring Plan”), resulting in certain management, facility and organizational changes. Under the 2020 Restructuring Plan, the Partnership expensed approximately $5.6 million in 2020 of costs associated with its restructuring activities. These activities consisted primarily of employee-related severance costs, and are included within the General and administrative caption on the consolidated statement of operations.

2019 Restructuring Activities. In 2019, management approved and initiated a plan to restructure its operations (“2019 Restructuring Plan”), resulting in certain management, facility and organizational changes. Under the 2019 Restructuring Plan, the Partnership expensed approximately $3.5 million and $4.9 million in 2020 and 2019, respectively, of costs associated with its restructuring activities. These activities consisted primarily of employee-related costs and consulting costs in support of the project. These costs are included within the General and administrative caption on the consolidated statement of operations.

Details for the 2020 Restructuring Plan and the 2019 Restructuring Plan follow.

	Severance Charges				Other Restructuring Charges				Total Severance and Other
	2020		2019		2020		2019		2020		2019
	(In thousands)
2020 Restructuring Plan	$	5,591	$	—	$	56	$	—	$	5,647	$	—
2019 Restructuring Plan		2,159		3,767		1,293		1,187		3,452		4,954
	$	7,750	$	3,767	$	1,349	$	1,187	$	9,099	$	4,954

	Accrued December 31, 2018		Charges Incurred		Cash Payments			Accrued December 31, 2019		Charges Incurred		Cash Payments			Accrued December 31, 2020
	(In thousands)
Employee-related costs	$	—	$	3,767	$	(951	)	$	2,816	$	7,750	$	(7,018	)	$	3,548
Other		—		1,187		(1,187	)		—		1,349		(1,349	)		—
Total restructuring costs	$	—	$	4,954	$	(2,138	)	$	2,816	$	9,099	$	(8,367	)	$	3,548

SEGMENT INFORMATION

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

SEGMENT INFORMATION

20. SEGMENT INFORMATION

As of December 31, 2020, the Partnership’s reportable segments are:

•

the Utica Shale, which is served by Summit Utica;

•

Ohio Gathering, which includes the Partnership’s ownership interest in OGC and OCC;

•

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

•

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

•

the Permian Basin, which is served by Summit Permian;

•

the Piceance Basin, which is served by Grand River;

•

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

•

the Marcellus Shale, which is served by Mountaineer Midstream.

Until March 22, 2019, the Partnership owned Tioga Midstream, a crude oil, produced water and associated natural gas gathering system operating in the Williston Basin. Until December 1, 2019, the Partnership owned certain assets in the Red Rock Gathering system operating in the Piceance Basin. Refer to Note 16 to the consolidated financial statements for details on the sale of Tioga Midstream and on the sale of certain assets in the Red Rock Gathering system.

Each of the Partnership’s reportable segments provides midstream services in a specific geographic area. Reportable segments reflect the way in which the Partnership internally report’s the financial information used to make decisions and allocate resources in connection with its operations.

The Ohio Gathering reportable segment includes the Partnership’s investment in Ohio Gathering. Income or loss from equity method investees, as reflected on the statements of operations, relates to Ohio Gathering and is recognized and disclosed on a one-month lag see Note 7.

For the year ended December 31, 2020, other than the investment activity described in Note 7, Double E did not have any results of operations given that the Double E Project is currently under development. The Double E Project is expected to be operational in the fourth quarter of 2021.

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

Assets by reportable segment follow.

	December 31,
	2020		2019
	(in thousands)
Assets⁽¹⁾:
Utica Shale	$	209,425	$	206,368
Ohio Gathering		259,888		275,000
Williston Basin		425,873		452,152
DJ Basin		199,920		205,308
Permian Basin		165,765		185,708
Piceance Basin		579,800		631,140
Barnett Shale		336,629		350,638
Marcellus Shale		176,441		184,631
Total reportable segment assets		2,353,741		2,490,945
Corporate and Other		146,076		83,153
Total assets	$	2,499,817	$	2,574,098

⁽¹⁾ At December 31, 2020, Corporate and Other included $132.9 million relating to the Partnership’s investment in Double E (included in the Investment in equity method investees caption of the consolidated balance sheet). At December 31, 2019, Corporate and Other included $34.7 million relating to the Partnership’s investment in Double E (included in the Investment in equity method investees caption of the consolidated balance sheet).

Revenues by reportable segment follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Revenues:
Utica Shale	$	36,509	$	33,991
Williston Basin		92,695		105,651
DJ Basin		28,070		26,050
Permian Basin		29,533		20,303
Piceance Basin		113,890		133,638
Barnett Shale		54,459		71,802
Marcellus Shale		25,741		24,471
Total reportable segments revenue		380,897		415,906
Corporate and Other		2,576		30,552
Eliminations		—		(2,930	)
Total revenues	$	383,473	$	443,528

Counterparties accounting for a significant portion of total revenues were as follows:

	Year ended December 31,
	2020			2019
Percentage of total revenues⁽¹⁾:
Counterparty A - Piceance Basin		13	%		11	%
Counterparty B - Williston Basin	*				10	%
Counterparty C - Utica Shale		5	%	*
Counterparty C - Permian Basin		5	%	*
Counterparty C - Barnett Shale		1	%	*

* Less than 10%

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

	Year ended December 31,
	2020		2019
	(In thousands)
Depreciation and amortization:
Utica Shale	$	7,696	$	7,659
Williston Basin		25,911		19,829
DJ Basin		6,146		3,732
Permian Basin		5,455		4,868
Piceance Basin		45,203		47,018
Barnett Shale⁽¹⁾		16,112		16,575
Marcellus Shale		9,195		9,141
Total reportable segment depreciation and amortization		115,718		108,822
Corporate and Other		3,352		2,752
Total depreciation and amortization	$	119,070	$	111,574

⁽¹⁾ Includes the amortization expense associated with the Partnership’s favorable and unfavorable gas gathering contracts as reported in Other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Cash paid for capital expenditures:
Utica Shale	$	6,957	$	3,902
Williston Basin		8,767		30,861
DJ Basin		12,829		80,487
Permian Basin		7,014		44,955
Piceance Basin		1,370		1,946
Barnett Shale⁽¹⁾		1,878		184
Marcellus Shale		700		693
Total reportable segment capital expenditures		39,515		163,028
Corporate and Other		3,613		19,263
Total cash paid for capital expenditures	$	43,128	$	182,291

⁽¹⁾ For the year ended December 31, 2019, the amount includes sales tax reimbursements of $1.1 million.

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

The Partnership assesses the performance of its reportable segments based on segment adjusted EBITDA. The Partnership defines segment adjusted EBITDA as total revenues less total costs and expenses; plus (i) other income excluding interest income, (ii) 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) impairments (vii) other noncash expenses or losses, less other noncash income or gains and (ix) restructuring expenses. Proportional adjusted EBITDA for the Partnership’s equity method investees is defined as the product of (i) total revenues less total expenses, excluding impairments and other noncash income or expense items, and amortization for deferred contract costs; and (ii) ownership interest in Ohio Gathering during the respective period.

For the purpose of evaluating segment performance, the Partnership excludes the effect of Corporate and Other revenues and expenses, such as certain general and administrative expenses (including compensation-related expenses and professional services fees), certain natural gas and crude oil marketing services, transaction costs, interest expense and income tax expense or benefit from segment adjusted EBITDA.

Segment adjusted EBITDA by reportable segment follows.

	Year ended December 31,
	2020		2019
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	32,783	$	29,292
Ohio Gathering		31,056		39,126
Williston Basin		52,060		69,437
DJ Basin		19,449		18,668
Permian Basin		4,426		(879	)
Piceance Basin		88,820		98,765
Barnett Shale		32,093		43,043
Marcellus Shale		22,015		20,051
Total of reportable segments' measures of profit	$	282,702	$	317,503

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

	Year ended December 31,
	2020			2019
	(In thousands)
Reconciliation of income (loss) before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit:
Income (loss) before income taxes and income (loss) from equity method investees	$	177,661		$	(54,644	)
Add:
Corporate and Other expense		59,585			44,808
Interest expense		78,894			91,966
Gain on early extinguishment of debt		(203,062	)		—
Depreciation and amortization⁽¹⁾		119,070			111,574
Proportional adjusted EBITDA for equity method investees		31,056			39,126
Adjustments related to MVC shortfall payments		—			3,476
Adjustments related to capital reimbursement activity		(1,395	)		(2,156	)
Unit-based and noncash compensation		8,111			8,171
Gain on asset sales, net		(307	)		(1,536	)
Long-lived asset impairment		13,089			60,507
Goodwill impairment		—			16,211
Total of reportable segments' measures of profit	$	282,702		$	317,503

⁽¹⁾ Includes the amortization expense associated with the Partnership’s favorable gas gathering contracts as reported in other revenues.

For the years ended December 31, 2020 and 2019, adjustments related to MVC shortfall payments recognize the earnings from MVC shortfall payments ratably over the term of the associated MVC.

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

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Cash, Cash Equivalents and Restricted Cash

SUBSEQUENT EVENTS

12 Months Ended

Dec. 31, 2020

Subsequent Events [Abstract]

SUBSEQUENT EVENTS

21. SUBSEQUENT EVENTS

In January 2021, Double E received its Notice to Proceed with construction, as well as approval of its implementation plan, from FERC. With the receipt of the 7(c) certificate and the NTP, construction on the Double E pipeline commenced in February 2021, and the pipeline is expected to be in-service by the end of 2021.

In February 2021, Summit Permian Transmission, LLC, received $175.0 million of commitments to finance the development of the Double E Project. The lenders have committed to provide senior secured credit facilities consisting of a $160.0 million delayed draw term loan facility and a $15.0 million working capital facility (the “Credit Facilities”). The Credit Facilities

are non-recourse to SMLP and mature seven years after the date of initial borrowing. SMLP expects to close and fund on the Credit Facilities shortly and will post a $15.0 million letter of credit under its corporate revolving credit facility to support back-end equity contributions, if needed, upon first funding.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Cash, Cash Equivalents and Restricted Cash. The Partnership considers all highly liquid investments with an original maturity of three months or less to be cash equivalents.

Accounts Receivable

Property, Plant and Equipment

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

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

Asset Retirement Obligations

Amortizing Intangibles

Equity Method Investments

Impairment of Long-Lived Assets

Environmental Matters

Commitments and Contingencies

Noncontrolling Interest and Mezzanine Capital

Revenue Recognition

Revenue Recognition. The Partnership provides gathering and/or processing services principally under contracts that contain one or more of the following arrangements described below:

•

For the contracts described above, the Partnership reflects its revenues in the financial statement captions described below.

Financial statement caption:		Revenue description:
Revenues:
Gathering services and related fees		• Revenue earned from fee-based gathering, compression, treating and processing services;
Natural gas, NGLs and condensate sales		• Revenue from the sale of physical natural gas purchased from customers percent-of-proceeds arrangements (Costs are presented within cost of natural gas and NGLs);
		• Revenue from sale of condensate and NGLs retained from gathering services (Costs are presented within operation and maintenance expense); and
Other revenues		• Customer reimbursements to the Partnership for costs incurred by the Partnership on customer’s behalf (Recorded on a gross basis).

Unit-Based Compensation

Income Taxes

New Accounting Standards Implemented in this Annual Report

New accounting standards implemented in this Annual Report.

New accounting standards not yet implemented in this Annual Report.

Basis of Presentation

disclosure of commitments and contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Useful lives of Property, Plant and Equipment

Estimates of useful lives follow.

Useful lives

(In years)

Gathering and processing systems and related equipment

12-30

Other

4-15

REVENUE (Tables)

12 Months Ended

Dec. 31, 2020

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

	2021		2022		2023		2024		2025		Thereafter

Gathering services and related fees	$	100,182	$	84,215	$	66,330	$	49,872	$	32,996	$	22,706

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

Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 20.

	Year ended December 31, 2020
	Gathering services and related fees		Natural gas, NGLs and condensate sales		Other revenues		Total
	(in thousands)
Reportable Segments:
Utica Shale	$	36,509	$	—	$	—	$	36,509
Williston Basin		59,239		20,018		13,438		92,695
DJ Basin		23,868		245		3,957		28,070
Permian Basin		10,091		18,857		585		29,533
Piceance Basin		106,657		2,612		4,621		113,890
Barnett Shale		40,687		7,587		6,185		54,459
Marcellus Shale		25,741		—		—		25,741
Total reportable segments		302,792		49,319		28,786		380,897
All other segments		—		—		2,576		2,576
Total	$	302,792	$	49,319	$	31,362	$	383,473

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

Schedule of Information about Contract Assets from Contracts with Customers

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

	December 31, 2020			December 31, 2019
	(In thousands)
Contract assets, January 1, 2020	$	3,902		$	8,755
Additions		18,834			18,077
Transfers out		(20,710	)		(22,930	)
Contract assets, December 31, 2020	$	2,026		$	3,902

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on the Partnership’s property, plant and equipment follow.

	December 31, 2020			December 31, 2019
	(In thousands)
Gathering and processing systems and related equipment	$	2,213,501		$	2,182,950
Construction in progress		60,443			78,716
Land and line fill		10,440			10,137
Other		61,340			54,595
Total		2,345,724			2,326,398
Less accumulated depreciation		(528,178	)		(443,909	)
Property, plant and equipment, net	$	1,817,546		$	1,882,489

Schedule of depreciation expense and capitalized interest costs

Depreciation expense and capitalized interest for the Partnership follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Depreciation expense	$	86,263	$	78,489
Capitalized interest		3,878	$	6,974

AMORTIZING INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible assets and liabilities subject to amortization

Details regarding the Partnership’s intangible assets, all of which are subject to amortization, follow.

	December 31, 2020
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(16,064	)	$	8,131
Contract intangibles		278,448		(195,243	)		83,205
Rights-of-way		157,271		(49,041	)		108,230
Total intangible assets	$	459,914	$	(260,348	)	$	199,566

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

Recognized amortization expense in other revenues and cost and expenses

The Partnership recognized amortization expense of its favorable gas gathering contracts in Other revenues as follows:

	Year ended December 31,
	2020			2019
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(938	)	$	(1,220	)

The Partnership recognized amortization expense of its contract and right of way intangibles in costs and expenses as follows:

	Year ended December 31,
	2020		2019
	(In thousands)
Amortization expense – contract intangibles	$	25,694	$	25,587
Amortization expense – rights-of-way		6,175		6,278

Estimated aggregate annual amortization expected to be recognized

The Partnership’s estimated aggregate annual amortization expected to be recognized as of December 31, 2020 for each of the five succeeding fiscal years follows.

	Intangible assets
	(In thousands)
2021	$	28,212
2022		25,145
2023		25,091
2024		14,920
2025		14,898

EQUITY METHOD INVESTMENTS (Tables)

12 Months Ended

Dec. 31, 2020

Equity Method Investments And Joint Ventures [Abstract]

Equity Method Investments

	2020		2019
	(In thousands)
Investment in Ohio Gathering, December 31,	$	259,888	$	275,000
December cash distributions		2,748		2,700
Impairment loss⁽¹⁾		—		232,521
Basis difference		216,591		—
Investment in Ohio Gathering (Books and records), November 30,	$	479,227	$	510,221

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

	November 30, 2020				November 30, 2019
	OGC		OCC		OGC		OCC
	(In thousands)
Current assets	$	32,404	$	4,902	$	41,972	$	2,187
Noncurrent assets		1,240,090		290		1,281,171		28,323
Total assets	$	1,272,494	$	5,192	$	1,323,143	$	30,510

Current liabilities	$	8,424	$	2,982	$	21,798	$	4,016
Noncurrent liabilities		8,441		5,146		4,113		6,683
Total liabilities	$	16,865	$	8,128	$	25,911	$	10,699

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

	Twelve months ended November 30, 2020					Twelve months ended November 30, 2019
	OGC		OCC			OGC		OCC
	(In thousands)
Total revenues	$	114,524	$	12,931		$	142,138	$	8,601
Total operating expenses		103,020		38,502			108,234		38,815
Net income (loss)		11,496		(25,571	)		33,897		(30,214	)

DEFERRED REVENUE (Tables)

12 Months Ended

Dec. 31, 2020

Rollforward of deferred revenue

A rollforward of current deferred revenue follows.

	Total
	(In thousands)
Current deferred revenue, January 1, 2020	$	13,493
Additions		2,731
Less: revenue recognized		6,236
Current deferred revenue, December 31, 2020	$	9,988

A rollforward of noncurrent deferred revenue follows.

	Total
	(In thousands)
Noncurrent deferred revenue, January 1, 2020	$	38,709
Additions		19,384
Less: reclassification to current deferred revenue		9,843
Noncurrent deferred revenue, December 31, 2020	$	48,250

DEBT (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Schedule of debt and capital leases

Debt for the Partnership at December 31, 2020 and 2019 follows.

	December 31, 2020			December 31, 2019
	(In thousands)
Revolving Credit Facility: Summit Holdings' variable rate senior secured Revolving Credit Facility (2.90% at December 31, 2020 and 4.55% at December 31, 2019) due May 2022	$	857,000		$	677,000
ECP Loans: Summit Holdings' 8.00% senior secured term loan obtained in May 2020 and fully repaid in August 2020		—			—
2022 Senior Notes: Summit Holdings' 5.5% senior unsecured notes due August 2022		234,047			300,000
Less: unamortized debt issuance costs (1)		(859	)		(1,686	)
2025 Senior Notes: Summit Holdings' 5.75% senior unsecured notes due April 2025		259,463			500,000
Less: unamortized debt issuance costs (1)		(2,325	)		(5,015	)
SMPH Term Loan: SMP Holdings' variable rate senior secured term loan (7.80% at December 31, 2019) due May 2022 and extinguished in November 2020		—			161,500
Less: unamortized debt issuance costs (1)		—			(3,974	)
Total debt		1,347,326			1,627,825
Less: current portion		—			(5,546	)
Total long-term debt	$	1,347,326		$	1,622,279

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

Schedule of maturities of long-term debt

The aggregate amount of Partnership’s debt maturing during each of the years after December 31, 2020 are as follows (in thousands):

2021	$	—
2022		1,091,047
2023		—
2024		—
2025		259,463
Thereafter		—
Total long-term debt	$	1,350,510

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Liability Management Transactions [Abstract]

LIABILITY MANAGEMENT TRANSACTIONS (Tables)

12 Months Ended

Dec. 31, 2020

Schedule of extinguishment of debt

The Partnership recognized a $203.1 million gain on extinguishment of debt during the year ended December 31, 2020, the components of which are summarized in the table below.

	ECP Loan Repayment			Open Market Repurchases						Tender Offers						TL Restructuring			Total
				2022			2025			2022			2025
(in thousands)				Senior Notes			Senior Notes			Senior Notes			Senior Notes
Gain on Repurchases of Senior Notes and TL Restructuring	$	—		$	11,554		$	76,789		$	9,223		$	15,479		$	99,175		$	212,220
Debt issue costs		(361	)		(143	)		(1,541	)		(125	)		(351	)		(2,724	)		(5,245	)
Transaction costs		(249	)		(105	)		(105	)		(467	)		(467	)		(2,520	)		(3,913	)
Gain (loss) on debt extinguishment	$	(610	)	$	11,306		$	75,143		$	8,631		$	14,661		$	93,931		$	203,062

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of accrued environmental remediation

A rollforward of the Partnership’s undiscounted accrued environmental remediation liabilities related to the Meadowlark Rupture follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2019	$	5,636
Payments made		(2,284	)
Additional accruals		1,299
Accrued environmental remediation, December 31, 2019	$	4,651
Payments made		(1,722	)
Accrued environmental remediation, December 31, 2020	$	2,929

FINANCIAL INSTRUMENTS (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Summary of the estimated fair value of debt instruments

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

	December 31, 2020				December 31, 2019
	Carrying Value, Net		Estimated fair value (Level 2)		Carrying Value, Net		Estimated fair value (Level 2)
	(in thousands)
2022 Senior Notes	$	233,188	$	215,713	$	298,314	$	266,750
2025 Senior Notes		257,138		168,002		494,985		382,708

PARTNERS' CAPITAL AND MEZZANINE CAPITAL (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of partner units activity

A rollforward of the number of common limited partner units follows for the period from December 31, 2018 to December 31, 2020.

	Common Units⁽²⁾
Units, December 31, 2018		3,021,258
2019 activity		—
Units, December 31, 2019		3,021,258
GP Buy-In Transaction⁽¹⁾		(132,687	)
Common units issued for SMLP LTIP, net		95,987
TL Restructuring (Note 9)		2,306,972
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes		817,845
Other		717
Units, December 31, 2020		6,110,092

⁽²⁾ As adjusted for reverse unit split.

A rollforward of the number of Series A Preferred Units follows for the period from December 31, 2018 to December 31, 2020.

	Series A Preferred Units
Series A Preferred Units, December 31, 2018		300,000
2019 activity		—
Series A Preferred Units, December 31, 2019		300,000
Series A Preferred Unit Exchange Offer		(62,816	)
Series A Preferred Unit Tender		(75,075	)
Series A Preferred Units, December 31, 2020		162,109

Change in subsidiary

The following table shows the change in the Partnership’s Subsidiary Series A Preferred Unit balance during the year ended December 31, 2020:

	December 31, 2020
	(in thousands)
Balance at December 31, 2019	$	27,450
New issuances		50,000
PIK distributions		5,251
Issuance costs		(1,290	)
Redemption accretion		8,247
Balance at December 31, 2020⁽¹⁾	$	89,658

⁽¹⁾ Amount is net of $3.9 million of issuance costs at December 31, 2020.

Details of cash distributions

Cash Distributions Paid and Declared. Prior to the GP Buy-In Transaction, SMLP paid the following per-unit cash distributions to its unitholders during the years ended December 31:

	Year ended December 31,
	2020		2019
Per-unit distributions to unitholders	$	0.125	$	1.4375

EARNINGS PER UNIT (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of earnings per limited partner unit

The following table details the components of EPU.

	Year ended December 31,
	2020		2019
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net income (loss) among limited partner interests:
Net income (loss) attributable to limited partners	$	192,352	$	(184,451	)
Less:
Net income attributable to Series A Preferred Units		26,529		28,500
Net income attributable to Subsidiary Series A Preferred Units		13,498		58
Add:
Deemed capital contribution from Series A Preferred Unit Exchange Offer		54,945		—
Deemed capital contribution from Series A Preferred Tender Offer		55,724
Net income (loss) attributable to common limited partners	$	262,994	$	(213,009	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic⁽¹⁾		3,592		3,021
Effect of nonvested phantom units		102		—
Weighted-average common units outstanding – diluted		3,694		3,021

Net Income (Loss) per limited partner unit:
Common unit – basic	$	73.22	$	(70.50	)
Common unit – diluted	$	71.19	$	(70.50	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		240		12

⁽¹⁾

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)

12 Months Ended

Dec. 31, 2020

Supplemental Cash Flow Elements [Abstract]

Schedule of supplemental cash flow information

	Year ended December 31,
	2020		2019
	(In thousands)
Supplemental cash flow information:
Cash interest paid	$	79,450	$	92,536
Less capitalized interest		3,878		6,974
Interest paid (net of capitalized interest)	$	75,572	$	85,562

Cash paid for taxes	$	190	$	150

Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	$	6,154	$	19,846
Warrant issuance for GP Buy-In Transaction		2,300		—
Asset contribution to an equity method investment		—		23,643
Right-of-use assets relating to ASC Topic 842		3,685		5,448
Fair value of SMLP equity for TL Restructuring		30,521		—
Accretion of Subsidiary Series A Preferred Units		8,247		—

UNIT-BASED AND NONCASH COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of activity

The following table presents phantom unit activity for the periods presented:

	Units			Weighted-average grant date fair value
Nonvested phantom units, December 31, 2018		57,608		$	256.65
Phantom units granted		127,540			97.20
Phantom units vested		(40,174	)		251.70
Phantom units forfeited		(4,574	)		193.05
Nonvested phantom units, December 31, 2019		140,400			115.35
Phantom units granted		345,997			9.20
Phantom units vested		(193,349	)		54.07
Phantom units forfeited		(1,357	)		119.24
Nonvested phantom units, December 31, 2020		291,691		$	26.57

Schedule of intrinsic values

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

	Year ended December 31,
	2020		2019
	(In thousands)
Intrinsic value of vested LTIP awards	$	2,602	$	5,940

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

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

	Year ended December 31,
	2020		2019
	(In thousands)
SMLP LTIP unit-based compensation	$	8,111	$	8,171

LEASES (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Schedule of right-of-use assets and lease liabilities

	December 31, 2020		December 31, 2019
	(In thousands)

ROU assets
Operating	$	3,736	$	3,580
Finance		1,748		3,159
	$	5,484	$	6,739
Lease liabilities, current
Operating	$	2,298	$	1,221
Finance		618		1,246
	$	2,916	$	2,467
Lease liabilities, noncurrent
Operating	$	3,182	$	2,513
Finance		154		676
	$	3,336	$	3,189

Schedule of lease cost and other information

Lease cost and Other information follow:

	Year ended December 31,
	2020		2019
	(In thousands)
Lease cost
Finance lease cost:
Amortization of ROU assets (included in depreciation and amortization)	$	1,274	$	1,559
Interest on lease liabilities (included in interest expense)		52		102
Operating lease cost (included in general and administrative expense)		2,644		3,345
	$	3,970	$	5,006

	Year ended December 31,
	2020			2019
	(In thousands)
Other information
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from operating leases	$	1,472		$	3,396
Operating cash outflows from finance leases		52			102
Financing cash outflows from finance leases		1,150			1,873
ROU assets obtained in exchange for new operating lease liabilities		3,552			1,218
ROU assets obtained in exchange for new finance lease liabilities		133			1,350
Weighted-average remaining lease term (years) - operating leases		4.9			5.8
Weighted-average remaining lease term (years) - finance leases		1.4			2.0
Weighted-average discount rate - operating leases		5	%		5	%
Weighted-average discount rate - finance leases		4	%		4	%

Schedule of total rent expense related to operating leases

	Year ended December 31,
	2020		2019
	(In thousands)
Lease expense	$	3,436	$	4,038

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

Future minimum lease payments due under noncancelable leases at December 31, 2020, were as follows:

	December 31, 2020
	(In thousands)
	Operating		Finance
2021	$	1,750	$	655
2022		1,308		126
2023		854		42
2024		573		—
2025		464		—
2026		156		—
Thereafter		579		—
Total future minimum lease payments	$	5,684	$	823

RESTRUCTURING (Tables)

12 Months Ended

Dec. 31, 2020

Restructuring And Related Activities [Abstract]

Restructuring and Related Costs

Details for the 2020 Restructuring Plan and the 2019 Restructuring Plan follow.

	Severance Charges				Other Restructuring Charges				Total Severance and Other
	2020		2019		2020		2019		2020		2019
	(In thousands)
2020 Restructuring Plan	$	5,591	$	—	$	56	$	—	$	5,647	$	—
2019 Restructuring Plan		2,159		3,767		1,293		1,187		3,452		4,954
	$	7,750	$	3,767	$	1,349	$	1,187	$	9,099	$	4,954

	Accrued December 31, 2018		Charges Incurred		Cash Payments			Accrued December 31, 2019		Charges Incurred		Cash Payments			Accrued December 31, 2020
	(In thousands)
Employee-related costs	$	—	$	3,767	$	(951	)	$	2,816	$	7,750	$	(7,018	)	$	3,548
Other		—		1,187		(1,187	)		—		1,349		(1,349	)		—
Total restructuring costs	$	—	$	4,954	$	(2,138	)	$	2,816	$	9,099	$	(8,367	)	$	3,548

SEGMENT INFORMATION (Tables)

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

Schedule of assets by reportable segment

Assets by reportable segment follow.

	December 31,
	2020		2019
	(in thousands)
Assets⁽¹⁾:
Utica Shale	$	209,425	$	206,368
Ohio Gathering		259,888		275,000
Williston Basin		425,873		452,152
DJ Basin		199,920		205,308
Permian Basin		165,765		185,708
Piceance Basin		579,800		631,140
Barnett Shale		336,629		350,638
Marcellus Shale		176,441		184,631
Total reportable segment assets		2,353,741		2,490,945
Corporate and Other		146,076		83,153
Total assets	$	2,499,817	$	2,574,098

Schedule of segment reporting information

Revenues by reportable segment follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Revenues:
Utica Shale	$	36,509	$	33,991
Williston Basin		92,695		105,651
DJ Basin		28,070		26,050
Permian Basin		29,533		20,303
Piceance Basin		113,890		133,638
Barnett Shale		54,459		71,802
Marcellus Shale		25,741		24,471
Total reportable segments revenue		380,897		415,906
Corporate and Other		2,576		30,552
Eliminations		—		(2,930	)
Total revenues	$	383,473	$	443,528

	Year ended December 31,
	2020		2019
	(In thousands)
Depreciation and amortization:
Utica Shale	$	7,696	$	7,659
Williston Basin		25,911		19,829
DJ Basin		6,146		3,732
Permian Basin		5,455		4,868
Piceance Basin		45,203		47,018
Barnett Shale⁽¹⁾		16,112		16,575
Marcellus Shale		9,195		9,141
Total reportable segment depreciation and amortization		115,718		108,822
Corporate and Other		3,352		2,752
Total depreciation and amortization	$	119,070	$	111,574

⁽¹⁾ Includes the amortization expense associated with the Partnership’s favorable and unfavorable gas gathering contracts as reported in Other revenues.

Cash paid for capital expenditures by reportable segment follow.

	Year ended December 31,
	2020		2019
	(In thousands)
Cash paid for capital expenditures:
Utica Shale	$	6,957	$	3,902
Williston Basin		8,767		30,861
DJ Basin		12,829		80,487
Permian Basin		7,014		44,955
Piceance Basin		1,370		1,946
Barnett Shale⁽¹⁾		1,878		184
Marcellus Shale		700		693
Total reportable segment capital expenditures		39,515		163,028
Corporate and Other		3,613		19,263
Total cash paid for capital expenditures	$	43,128	$	182,291

⁽¹⁾ For the year ended December 31, 2019, the amount includes sales tax reimbursements of $1.1 million.

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

Counterparties accounting for a significant portion of total revenues were as follows:

	Year ended December 31,
	2020			2019
Percentage of total revenues⁽¹⁾:
Counterparty A - Piceance Basin		13	%		11	%
Counterparty B - Williston Basin	*				10	%
Counterparty C - Utica Shale		5	%	*
Counterparty C - Permian Basin		5	%	*
Counterparty C - Barnett Shale		1	%	*

* Less than 10%

Reconciliation of net income to adjusted EBITDA

Segment adjusted EBITDA by reportable segment follows.

	Year ended December 31,
	2020		2019
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	32,783	$	29,292
Ohio Gathering		31,056		39,126
Williston Basin		52,060		69,437
DJ Basin		19,449		18,668
Permian Basin		4,426		(879	)
Piceance Basin		88,820		98,765
Barnett Shale		32,093		43,043
Marcellus Shale		22,015		20,051
Total of reportable segments' measures of profit	$	282,702	$	317,503

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

	Year ended December 31,
	2020			2019
	(In thousands)
Reconciliation of income (loss) before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit:
Income (loss) before income taxes and income (loss) from equity method investees	$	177,661		$	(54,644	)
Add:
Corporate and Other expense		59,585			44,808
Interest expense		78,894			91,966
Gain on early extinguishment of debt		(203,062	)		—
Depreciation and amortization⁽¹⁾		119,070			111,574
Proportional adjusted EBITDA for equity method investees		31,056			39,126
Adjustments related to MVC shortfall payments		—			3,476
Adjustments related to capital reimbursement activity		(1,395	)		(2,156	)
Unit-based and noncash compensation		8,111			8,171
Gain on asset sales, net		(307	)		(1,536	)
Long-lived asset impairment		13,089			60,507
Goodwill impairment		—			16,211
Total of reportable segments' measures of profit	$	282,702		$	317,503

⁽¹⁾ Includes the amortization expense associated with the Partnership’s favorable gas gathering contracts as reported in other revenues.

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) $ in Millions		12 Months Ended
	Nov. 09, 2020 shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 shares
Organization And Business Operations [Line Items]
Purchase agreement date		May 28, 2020
Common limited partner capital (shares)		6,110,092	3,021,258
Summit Midstream GP, LLC \| Reverse Unit Split
Organization And Business Operations [Line Items]
Common limited partner capital (shares)	56,624,887	3,774,992
Reverse unit split ratio	0.06
Reverse unit split description	On November 9, 2020, after the close of trading on the NYSE, the Partnership effected a 1-for-15 reverse unit split (the “Reverse Unit Split”) of its common units. The common units began trading on a split-adjusted basis on November 10, 2020
Common units \| Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (shares)		0.4
Summit Midstream Partners Holdings L L C
Organization And Business Operations [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan		2,300,000
SMLP common units not pledged as collateral under the SMPH Term Loan		700,000
Common units retire		1,100,000
Summit Investments
Organization And Business Operations [Line Items]
Cash paid to Acquire investment \| $		$ 35.0
Summit Investments \| Common units
Organization And Business Operations [Line Items]
Number of common units purchased.		700,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Gathering and processing systems and related equipment \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	12 years
Gathering and processing systems and related equipment \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	30 years
Other \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	4 years
Other \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	15 years

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies [Line Items]
Asset retirement obligation	$ 0	$ 0
Favorable gas gathering contracts \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	10 years
Favorable gas gathering contracts \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	20 years
Other Gas Gathering Contract \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	3 years
Other Gas Gathering Contract \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	25 years
Rights-of-way \| Minimum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	20 years
Rights-of-way \| Maximum
Summary of Significant Accounting Policies [Line Items]
Useful lives (In years)	30 years

REVENUE - Narrative1 (Details)	Dec. 31, 2020
Maximum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	25 years

REVENUE - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
REVENUE - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue From Contract With Customer [Line Items]
Revenue, performance obligation, description of payment terms	Services are typically billed on a monthly basis and the Partnership does not offer extended payment terms. The Partnership does not have contracts with financing components.
Receivables with customers	$ 57,500	$ 90,400
Contract assets included in accounts receivable	2,026	3,902	$ 8,755
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 4,000	$ 10,100

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) - Gathering Services and Related Fees $ in Thousands	Dec. 31, 2020 USD ($)
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	$ 100,182
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 84,215
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 66,330
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 49,872
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 32,996
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period
Revenue, remaining performance obligation	$ 22,706

REVENUE - Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 383,473	$ 443,528
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	2,576	27,622
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	380,897	415,906
Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	36,509	33,991
Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	92,695	105,651
Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	28,070	26,050
Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	29,533	20,303
Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	113,890	133,638
Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	54,459	71,802
Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	25,741	24,471
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues	302,792	326,747
Gathering Services and Related Fees \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	(2,045)
Gathering Services and Related Fees \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	302,792	328,792
Gathering Services and Related Fees \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	36,509	31,926
Gathering Services and Related Fees \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	59,239	77,626
Gathering Services and Related Fees \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	23,868	21,940
Gathering Services and Related Fees \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	10,091	3,610
Gathering Services and Related Fees \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	106,657	121,357
Gathering Services and Related Fees \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	40,687	47,862
Gathering Services and Related Fees \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	25,741	24,471
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues	49,319	86,994
Natural Gas, NGLs and Condensate Sales \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	28,660
Natural Gas, NGLs and Condensate Sales \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	49,319	58,334
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	20,018	16,461
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	245	389
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	18,857	16,383
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	2,612	7,954
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,587	17,147
Natural Gas, NGLs and Condensate Sales \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
Other Revenues
Disaggregation Of Revenue [Line Items]
Total revenues	31,362	29,787
Other Revenues \| All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	2,576	1,007
Other Revenues \| Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	28,786	28,780
Other Revenues \| Reportable Segments \| Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	2,065
Other Revenues \| Reportable Segments \| Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	13,438	11,564
Other Revenues \| Reportable Segments \| DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	3,957	3,721
Other Revenues \| Reportable Segments \| Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	585	310
Other Revenues \| Reportable Segments \| Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,621	4,327
Other Revenues \| Reportable Segments \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,185	6,793
Other Revenues \| Reportable Segments \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	$ 0	$ 0

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Contract With Customer Asset And Liability [Abstract]
Contract assets, beginning of period	$ 3,902	$ 8,755
Additions	18,834	18,077
Transfers out	(20,710)	(22,930)
Contract assets, end of period	$ 2,026	$ 3,902

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,345,724	$ 2,326,398
Less accumulated depreciation	(528,178)	(443,909)
Property, plant and equipment, net	1,817,546	1,882,489
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,213,501	2,182,950
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	60,443	78,716
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,440	10,137
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 61,340	$ 54,595

PROPERTY, PLANT, AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Impairment of property, plant and equipment	$ 13.1	$ 59.4
Asset impairment charges	5.1	14.2
DJ Basin
Property, Plant and Equipment [Line Items]
Asset impairment charges	$ 3.6	34.7
Barnett Shale \| Fixed Assets
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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 86,263	$ 78,489
Capitalized interest	$ 3,878	$ 6,974

AMORTIZING INTANGIBLE ASSETS - Intangible Assets and Liabilities Subject to Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 459,914	$ 459,818
Accumulated amortization	(260,348)	(227,540)
Net	199,566	232,278
Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24,195	24,195
Accumulated amortization	(16,064)	(15,125)
Net	8,131	9,070
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	278,448	278,448
Accumulated amortization	(195,243)	(169,549)
Net	83,205	108,899
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	157,271	157,175
Accumulated amortization	(49,041)	(42,866)
Net	$ 108,230	$ 114,309

AMORTIZING INTANGIBLE ASSETS - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Other Revenue \| Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (938)	$ (1,220)
Costs And Expenses \| Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	25,694	25,587
Costs And Expenses \| Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 6,175	$ 6,278

AMORTIZING INTANGIBLE ASSETS - Estimated Aggregate Annual Amortization Expected to be Recognized (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Intangible assets
2021	$ 28,212
2022	25,145
2023	25,091
2024	14,920
2025	$ 14,898

GOODWILL - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
GOODWILL - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill impairment	$ 0	$ 16,211
Mountaineer Midstream
Goodwill [Line Items]
Goodwill impairment		$ 16,200
Goodwill	$ 0

EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($)
$ in Thousands

11 Months Ended

12 Months Ended

Nov. 30, 2019

^[1]

Dec. 31, 2020

Dec. 31, 2019

Schedule Of Equity Method Investments [Line Items]

Asset contribution to an equity method investment

$ 23,643

Cash distribution to partnership

$ 0

7,313

Capitalized interest paid

3,878

6,974

Schedule Of Equity Method Investments [Line Items]

(11,271)

337,851

Double E

Additional cash investments

99,900

18,300

Capitalized interest paid

2,700

1,100

Capitalized legal costs

700

Net Assets

132,900

34,700

Result of operations

$ 0

Double E | Principal Owner

Schedule Of Equity Method Investments [Line Items]

Percentage of ownership interest

70.00%

Asset contribution to an equity method investment

$ 23,600

Cash distribution to partnership

$ 7,300

Double E | JV Partner

Schedule Of Equity Method Investments [Line Items]

Percentage of ownership interest

30.00%

Cash contribution

$ 7,300

OGC | Summit Midstream Partners, LLC

Schedule Of Equity Method Investments [Line Items]

WeightedAverageDiscountRatePercent1

$ 232,521

$ 329,700

329,700

9.00%

OGC | Summit Midstream Partners, LLC | Long Lived Assets

Schedule Of Equity Method Investments [Line Items]

Schedule Of Equity Method Investments [Line Items]

$ 6,300

OGC | Principal Owner

Percentage of ownership interest

38.20%

38.50%

[1]

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

11 Months Ended

12 Months Ended

Nov. 30, 2020

Nov. 30, 2019

Dec. 31, 2020

Dec. 31, 2019

Equity Method Investment [Roll Forward]

Investment in Ohio Gathering, December 31,

$ 309,728

December cash distributions

28,185

$ 37,300

Investment in Ohio Gathering, November 30,

(11,271)

337,851

392,740

309,728

Investment in equity method investees

309,728

OGC | Summit Midstream Partners, LLC

Equity Method Investment [Roll Forward]

Investment in Ohio Gathering, December 31,

259,888

$ 275,000

259,888

275,000

December cash distributions

2,748

2,700

Investment in Ohio Gathering, November 30,

232,521

^[1]

329,700

Basis difference

216,591

479,227

510,221

259,888

Investment in equity method investees

$ 479,227

$ 510,221

$ 259,888

$ 275,000

[1]

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

11 Months Ended

12 Months Ended

Nov. 30, 2019

^[1]

Dec. 31, 2020

Dec. 31, 2019

Schedule Of Equity Method Investments [Line Items]

OGC | Summit Midstream Partners, LLC

$ (11,271)

$ 337,851

Schedule Of Equity Method Investments [Line Items]

Write-off basis difference

$ 232,521

329,700

$ 329,700

103,500

OCC | Summit Midstream Partners, LLC

Schedule Of Equity Method Investments [Line Items]

$ 6,300

[1]

EQUITY METHOD INVESTMENTS - Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Nov. 30, 2020	Dec. 31, 2019	Nov. 30, 2019
Schedule Of Equity Method Investments [Line Items]
Current assets	$ 82,099		$ 139,861
TOTAL ASSETS	2,499,817		2,574,098
Current liabilities	68,408		89,547
Total liabilities	$ 1,487,268		$ 1,761,412
OGC \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule Of Equity Method Investments [Line Items]
Current assets		$ 32,404		$ 41,972
Noncurrent assets		1,240,090		1,281,171
TOTAL ASSETS		1,272,494		1,323,143
Current liabilities		8,424		21,798
Noncurrent liabilities		8,441		4,113
Total liabilities		16,865		25,911
OCC \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule Of Equity Method Investments [Line Items]
Current assets		4,902		2,187
Noncurrent assets		290		28,323
TOTAL ASSETS		5,192		30,510
Current liabilities		2,982		4,016
Noncurrent liabilities		5,146		6,683
Total liabilities		$ 8,128		$ 10,699

EQUITY METHOD INVESTMENTS - Statements of Operations Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Nov. 30, 2020	Dec. 31, 2019	Nov. 30, 2019
Schedule Of Equity Method Investments [Line Items]
Net income (loss)	$ 189,078		$ (393,726)
OGC \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule Of Equity Method Investments [Line Items]
Result of operations		$ 114,524		$ 142,138
Total operating expenses		103,020		108,234
Net income (loss)		11,496		33,897
OCC \| Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule Of Equity Method Investments [Line Items]
Result of operations		12,931		8,601
Total operating expenses		38,502		38,815
Net income (loss)		$ (25,571)		$ (30,214)

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

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 13,493
Current deferred revenue, Additions	2,731
Current deferred revenue, Less revenue recognized	6,236
Current deferred revenue, ending balance	9,988
Noncurrent deferred revenue, beginning balance	38,709
Noncurrent deferred revenue, Additions	19,384
Noncurrent deferred revenue, Less reclassification to current deferred revenue	9,843
Noncurrent deferred revenue, ending balance	$ 48,250

DEBT - Components of Long-Term Debt (Details) - USD ($)
$ in Thousands

Dec. 31, 2020

Dec. 31, 2019

Summit Midstream Partners Holdings L L C

Total debt

$ 1,350,510

Less: current portion

$ (5,546)

Long-term debt

1,347,326

1,622,279

Summit Midstream Partners Holdings L L C | Senior Secured Revolving Credit Facility Due May 2022

Total debt

1,347,326

1,627,825

Less: current portion

(5,546)

Long-term debt

1,347,326

1,622,279

Revolving credit facility

857,000

677,000

Summit Midstream Partners Holdings L L C | Senior Secured Term Loan Fully Paid August 2020

Revolving credit facility

Summit Midstream Partners Holdings L L C | 5.5% Senior Notes

Less unamortized debt issuance costs

Unsecured notes

259,463

500,000

^[1]

(2,325)

(5,015)

Summit Midstream Partners Holdings L L C | Senior Notes Due August 2022

Less unamortized debt issuance costs

Unsecured notes

234,047

300,000

^[1]

(859)

(1,686)

Summit Midstream Partners Holdings L L C | Senior Secured Term Loan Due May 2022

Revolving credit facility

161,500

Less unamortized debt issuance costs

^[1]

$ 0

$ (3,974)

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

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - Summit Midstream Partners Holdings L L C	Dec. 31, 2020	Dec. 31, 2019
Senior Secured Term Loan Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate		7.80%
Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	2.90%	4.55%
5.5% Senior Notes
Line of Credit Facility [Line Items]
Stated interest rate	5.75%	5.75%
Senior Secured Term Loan Fully Paid August 2020
Line of Credit Facility [Line Items]
Stated interest rate	8.00%	8.00%

DEBT - Maturities (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Debt
2021	$ 0
2022	1,091,047
2023	0
2024	0
2025	259,463
Thereafter	0
Total long-term debt	$ 1,350,510

DEBT - Revolving Credit Facility (Narrative) (Details) - Revolving credit facility		12 Months Ended
	Dec. 18, 2020 USD ($)	Dec. 31, 2020 USD ($)	May 25, 2017
Line of Credit Facility [Line Items]
Borrowing capacity		$ 1,100,000,000
Revolving credit facility maturity date		2022-05
Borrowing Capacity		$ 105,000,000
Accordion feature	$ 250,000,000.0
Senior secured leverage ratio	3.75
First lien net leverage ratio	3.50
Commitment fee on unused portion of the facility		0.50%
Interest rate at period end		2.90%
Unused portion under the facility		$ 238,900,000
Line of credit facility, outstanding amount		4,100,000
Cumulative payment obligations, maximum		50,000,000.0
Debt issuance costs		$ 7,400,000
LIBOR
Line of Credit Facility [Line Items]
Pricing tier ( L+ 325 bps)	3.25%	2.75%
Maximum
Line of Credit Facility [Line Items]
Borrowing Capacity	$ 1,250,000,000
Leverage ratio	5.75
Commitment fee on unused portion of the facility		0.50%
Ratio of total net indebtedness to consolidated trailing 12-month EBITDA		5.75
Ratio of first lien net indebtedness to consolidated trailing 12-month EBITDA		3.75
Maximum \| LIBOR
Line of Credit Facility [Line Items]
Pricing tier ( L+ 325 bps)		3.25%
Maximum \| ABR
Line of Credit Facility [Line Items]
Pricing tier ( L+ 325 bps)		2.25%
Minimum
Line of Credit Facility [Line Items]
Borrowing Capacity	$ 1,100
Leverage ratio			5.50
Leverage ratio	5.00
Commitment fee on unused portion of the facility		0.30%
Ratio of consolidated trailing 12-month EBITDA to net interest expense		2.5
Minimum \| LIBOR
Line of Credit Facility [Line Items]
Pricing tier ( L+ 325 bps)		1.75%
Minimum \| ABR
Line of Credit Facility [Line Items]
Pricing tier ( L+ 325 bps)		0.75%
Junior Lien \| Maximum
Line of Credit Facility [Line Items]
Accordion feature	$ 400,000,000.0

DEBT - ECP Loans (Narrative) (Details) $ in Millions	May 28, 2020 USD ($)
Debt Instrument [Line Items]
Line of credit facility description	(i) a Term Loan Credit Agreement (the “ECP NewCo Term Loan Credit Agreement”), with SMP TopCo, LLC, a Delaware limited liability company and affiliate of ECP (“ECP NewCo”), as lender and administrative agent, and Mizuho Bank (USA) (“Mizuho”), as collateral agent, in a principal amount of $28.2 million (the “ECP NewCo Loan”), and (ii) a Term Loan Credit Agreement (the “ECP Holdings Term Loan Credit Agreement” and together with the ECP NewCo Term Loan Credit Agreement, the “ECP Term Loan Credit Agreements”), with ECP Holdings, as lender, and ECP NewCo, as administrative agent and Mizuho, as collateral agent, in a principal amount of $6.8 million (the “ECP Holdings Loan” and together with the ECP NewCo Loan, the “ECP Loans”). The ECP Loans were set to mature on March 31, 2021 and bore interest at a fixed rate of 8.00% per annum, with the interest payment due at maturity of the ECP Loans. With borrowings under the Partnership’s Revolving Credit Facility, the Partnership fully repaid all amounts outstanding under the ECP Loans ($35 million of principal and $0.6 million of accrued interest) on August 7, 2020.
ECP NewCo Term Loan Credit Agreement [Member]
Debt Instrument [Line Items]
Debt instrument principal amount	$ 28.2
ECP Term Loan Credit Agreements [Member]
Debt Instrument [Line Items]
Debt instrument principal amount	$ 6.8
Maturity date	Mar. 31, 2021
Stated interest rate	8.00%
Repayments of loans	$ 35.0
Accrued interest on loan	$ 0.6

DEBT - Senior Notes (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
DEBT - Senior Notes (Narrative) (Details) - USD ($)	Jul. 31, 2014	Dec. 31, 2020
2022 Senior Note
Debt Instrument [Line Items]
Debt issuance costs	$ 5,100,000
2025 Senior Notes
Debt Instrument [Line Items]
Deferred issuance costs		$ 7,700
Summit Holdings and Finance Corporation \| 2022 Senior Note
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount	100.00%
Summit Holdings and Finance Corporation \| 2025 Senior Notes \| Redemption period one
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount		104.313%
Summit Holdings and Finance Corporation \| 2025 Senior Notes \| Redemption period two
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount		102.875%
Summit Holdings and Finance Corporation \| 2025 Senior Notes \| Redemption period three
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount		100.00%

DEBT - Liability Management Transactions (Narrative) (Details) - Liability Management Transactions - SMPH Term Loan Restructuring $ in Millions	Nov. 17, 2020 USD ($) shares
Debt Instrument [Line Items]
Term Loan result in consensual debt discharge of full amount owed under Term Loan exchange	$ 155.2
Capital stock issued	$ 2.3
Common stock held \| shares	2,306,972
Cash payment on the deferred purchase price obligation	$ 26.5
LIBOR
Debt Instrument [Line Items]
Pricing tier ( L+ 325 bps)	6.00%
ABR
Debt Instrument [Line Items]
Pricing tier ( L+ 325 bps)	5.00%

LIABILITY MANAGEMENT TRANSACTIONS (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 17, 2020	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Debt Instrument [Line Items]
Early extinguishment of debt		$ 306,500
Gain on early extinguishment of debt		203,062	$ 0
Open Market Repurchases \| Liability Management Transactions
Debt Instrument [Line Items]
Cash consideration paid		150,300
Gain on early extinguishment of debt		86,400
Open Market Repurchases \| Liability Management Transactions \| Senior Notes Due 2022
Debt Instrument [Line Items]
Senior Notes repurchased		32,400
Open Market Repurchases \| Liability Management Transactions \| 5.5% Senior Notes
Debt Instrument [Line Items]
Senior Notes repurchased		201,800
Tender Offers \| Liability Management Transactions
Debt Instrument [Line Items]
Cash consideration paid				$ 48,700
Gain on early extinguishment of debt		$ 23,300
Tender Offers \| Liability Management Transactions \| Senior Notes Due 2022
Debt Instrument [Line Items]
Senior Notes repurchased				33,500
Tender Offers \| Liability Management Transactions \| 5.5% Senior Notes
Debt Instrument [Line Items]
Senior Notes repurchased				$ 38,700
SMPH Term Loan Restructuring \| Liability Management Transactions
Debt Instrument [Line Items]
Gain on early extinguishment of debt	$ 94,000
Extinguishment of debt, gain (loss), per share, net of tax	$ 26.15

LIABILITY MANAGEMENT TRANSACTIONS - Gain on Extinguishment of Debt (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Gain on early extinguishment of debt	$ 203,062	$ 0
Liability Management Transactions \| Open Market Repurchases And Tender Offer Repurchase
Debt Instrument [Line Items]
Gain on early extinguishment of debt	$ 203,100

LIABILITY MANAGEMENT TRANSACTIONS - Schedule of Extinguishment of Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	$ 212,220
Debt issue costs	(5,245)
Transaction costs	(3,913)
Gain (loss) on debt extinguishment	203,062	$ 0
ECP Loan Repayment
Extinguishment Of Debt [Line Items]
Debt issue costs	(361)
Transaction costs	(249)
Gain (loss) on debt extinguishment	(610)
T L Restructuring
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	99,175
Debt issue costs	(2,724)
Transaction costs	(2,520)
Gain (loss) on debt extinguishment	93,931
Senior Notes Due 2022 \| Open Market Repurchases
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	11,554
Debt issue costs	(143)
Transaction costs	(105)
Gain (loss) on debt extinguishment	11,306
Senior Notes Due 2022 \| Tender Offers
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	9,223
Debt issue costs	(125)
Transaction costs	(467)
Gain (loss) on debt extinguishment	8,631
Senior Notes Due 2025 \| Open Market Repurchases
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	76,789
Debt issue costs	(1,541)
Transaction costs	(105)
Gain (loss) on debt extinguishment	75,143
Senior Notes Due 2025 \| Tender Offers
Extinguishment Of Debt [Line Items]
Gain on Repurchases of Senior Notes and TL Restructuring	15,479
Debt issue costs	(351)
Transaction costs	(467)
Gain (loss) on debt extinguishment	$ 14,661

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - Meadowlark Midstream Gathering System	12 Months Ended
	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Legal fines and other fees	$ 2,500,000
Accrued loss contingency	17,000,000.0
Maximum \| Principal Owner
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy	25,000,000.0
Coverage from property and business interruption insurance policy	$ 200,000,000.0

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 4,651	$ 5,636
Payments made	(1,722)	(2,284)
Additional accruals		1,299
Accrued environmental remediation, ending balance	$ 2,929	$ 4,651

FINANCIAL INSTRUMENTS - Concentration Risk - Narrative (Details) - Customer	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
CONCENTRATIONS OF RISK
Number of top customers	5
Five Largest Customers \| Accounts receivable \| Customer Concentration Risk
CONCENTRATIONS OF RISK
Concentration risk, percentage	51.00%	46.00%

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Carrying Value, Net \| Senior Notes Due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 233,188	$ 298,314
Carrying Value, Net \| 2025 Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	257,138	494,985
Fair Value \| Senior Notes Due 2022 \| Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	215,713	266,750
Fair Value \| 2025 Senior Notes \| Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 168,002	$ 382,708

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended					12 Months Ended
	Jan. 29, 2020	Jan. 21, 2020	Dec. 31, 2020	Jul. 31, 2020	May 28, 2020	Mar. 31, 2019	Nov. 30, 2017	Dec. 31, 2020	Dec. 31, 2019
Partners Capital [Line Items]
Preferred units issued			162,109					162,109	300,000
Repayment of outstanding revolving credit facility								$ 69,300	$ 158,000
Maximum period following end of quarter to distribute all available cash								45 days
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.125							$ 0.125	$ 1.4375
Cash paid to unit holders	$ 11,700
Cash distribution date	Feb. 14, 2020
Cash distribution date of record	Feb. 07, 2020
Revolving credit facility
Partners Capital [Line Items]
Repayment of outstanding revolving credit facility							$ 293,200
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued			55,251				300,000	55,251
Interest in partnership per unit							$ 1,000
Distribution rate							9.50%	7.00%
Liquidation preference per unit			$ 1,000				$ 1,000	$ 1,000
Distribution percentage of liquidation preference rate description								three-month LIBOR plus a spread of 7.43%
Series A preferred per unit, price			$ 1,000					$ 1,000
Proceeds from issuance of common limited partners units								$ 48,700
Redemption amount			$ 106,600					106,600
Series A Preferred Units \| Permian Holdco
Partners Capital [Line Items]
Preferred units issued									30,000
Series A preferred per unit, price									$ 1,000
Series A Preferred Units \| Double E Pipeline L L C \| Permian Holdco
Partners Capital [Line Items]
Proceeds from issuance of common limited partners units									$ 27,400
Series A Preferred Units \| Paid-in-kind
Partners Capital [Line Items]
Distribution percentage of subsidiary unit		7.00%
Distribution percentage of liquidation preference rate of undrawn commitment units		1.00%
Series A Preferred Units \| LIBOR
Partners Capital [Line Items]
Distribution percentage of liquidation preference rate							7.43%
General Partner \| Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner interest						2.00%
Series A Preferred Units \| Preferred Stock Exchange Offer
Partners Capital [Line Items]
Preferred units issued				62,816
Common units \| Energy Capital Partners
Partners Capital [Line Items]
Number of common units purchased.					500,000
Exercise price of Warrants					$ 15.35
Valuation of warrants			$ 1,900		$ 2,300			$ 1,900
Warrant or right, reason for issuance, description					Upon exercise of the ECP Warrants, each of ECP NewCo and ECP Holdings may receive, at its election: (i) a number of SMLP common units equal to the number of SMLP common units for which the ECP Warrants are being exercised, if exercising the ECP Warrants by cash payment of the exercise price; (ii) a number of SMLP common units equal to the product of the number of common units being exercised multiplied by (a) the difference between the average of the daily volume-weighted average price (“VWAP”) of the SMLP common units on the New York Stock Exchange (the “NYSE”) on each of the three trading days prior to the delivery of the notice of exercise (the “VWAP Average”) and the exercise price (the “VWAP Difference”), divided by (b) the VWAP Average; and/or (iii) an amount in cash, to the extent that the Partnership’s leverage ratio would be at least 0.5x less than the maximum applicable ratio set forth in the Revolving Credit Facility, equal to the product of (a) the number of SMLP common units exercised and (b) the VWAP Difference, subject to certain adjustments under the ECP Warrants.
Warrants exercisable date					May 28, 2023
Common units \| Energy Capital Partners \| ECP Holdings Warrant
Partners Capital [Line Items]
Number of common units purchased.					100,000
Common units \| Maximum \| Energy Capital Partners
Partners Capital [Line Items]
Exercise price of Warrants					$ 30.00
Common units, issued					0.7
Common units \| Preferred Stock Exchange Offer
Partners Capital [Line Items]
General partner units converted				837,547
Common units \| Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner units converted						600,000
Series A Preferred Units \| Tender offer
Partners Capital [Line Items]
Number of shares purchased			75,075
Number of shares purchased, value			$ 25,000
Purchase price per share			$ 333.00

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Schedule of Units (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Common Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	3,021,258	3,021,258
2019 activity		0
GP Buy-In Transaction(1)	(132,687)
Common units issued for SMLP LTIP, net	95,987
TL Restructuring (Note 9)	2,306,972
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes	817,845
Other	717
Units, ending balance (in shares)	6,110,092	3,021,258
Series A Preferred Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	300,000	300,000
2019 activity		0
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes	(62,816)
Units, ending balance (in shares)	162,109	300,000
Series A Preferred Unit Tender	(75,075)

PARTNERS' CAPITAL AND MEZZANINE CAPITAL- Change in Subsidiary (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) shares
Partners Capital [Line Items]
Issuance costs	$ (3,900,000)
Series A Preferred Units
Partners Capital [Line Items]
Beginning Balance	$ 27,450,000
New issuances \| shares	50,000
PIK distributions \| shares	5,251
Issuance costs	$ (1,290,000)
Redemption accretion	8,247,000
Ending Balance	$ 89,658,000

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Parenthetical (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Equity [Abstract]
Issuance costs	$ 3.9

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares		12 Months Ended
	Jan. 29, 2020	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.125	$ 0.125	$ 1.4375

EARNINGS PER UNIT (Details) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

Deemed capital contribution from Series A Preferred Unit Exchange Offer

$ 192,352

$ (184,451)

$ 110,669

$ 0

Phantom Units

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

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

240

Limited Partner Interest Before Subordinated Units Converted To Common Units

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

$ 192,352

$ (184,451)

Series A Preferred Units

Deemed capital contribution from Series A Preferred Unit Exchange Offer

26,529

28,500

54,945

Deemed capital contribution from Series A Preferred Tender Offer

55,724

Series A Preferred Units | Subsidiaries

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]

13,498

Common units