Summit Midstream Partners (SMLP) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Mar. 31, 2021
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		6,744,736
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Title of 12(b) Security	Common Units
Trading Symbol	SMLP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-35666
Entity Tax Identification Number	45-5200503
Entity Address, Address Line One	910 Louisiana Street
Entity Address, Address Line Two	Suite 4200
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	832
Local Phone Number	413-4770
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Document Transition Report	false
Entity Incorporation, State or Country Code	DE

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 2021	Dec. 31, 2020
Subsidiary Series A preferred unitholders, issued	162,109	162,109
Subsidiary Series A preferred unitholders, outstanding	162,109	162,109
Common limited partner capital (in shares), issued	6,206,021	6,110,092
Common limited partner capital (in shares), outstanding	6,206,021	6,110,092
Mezzanine Capital
Subsidiary Series A preferred unitholders, issued	86,802	85,308
Subsidiary Series A preferred unitholders, outstanding	86,802	85,308

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
ASSETS
Cash and cash equivalents	$ 16,233	$ 15,544
Restricted cash	8,067
Accounts receivable, net	54,301	61,932
Other current assets	12,167	4,623
Total current assets	90,768	82,099
Property, plant and equipment, net	1,788,222	1,817,546
Intangible assets, net	192,378	199,566
Investment in equity method investees	394,405	392,740
Other noncurrent assets	6,792	7,866
TOTAL ASSETS	2,472,565	2,499,817
LIABILITIES AND CAPITAL
Trade accounts payable	15,873	11,878
Accrued expenses	11,666	13,036
Deferred revenue	10,017	9,988
Ad valorem taxes payable	7,589	9,086
Accrued compensation and employee benefits	4,481	9,658
Accrued interest	8,512	8,007
Accrued environmental remediation	1,885	1,392
Other current liabilities	14,682	5,363
Total current liabilities	74,705	68,408
Long-term debt	1,304,918	1,347,326
Noncurrent deferred revenue	47,644	48,250
Noncurrent accrued environmental remediation	1,368	1,537
Other noncurrent liabilities	21,700	21,747
Total liabilities	1,450,335	1,487,268
Commitments and contingencies (Note 13)
Mezzanine Capital
Subsidiary Series A Preferred Units (86,802 and 85,308 units issued and outstanding at March 31, 2021 and December 31, 2020, respectively)	93,590	89,658
Partners' Capital
Series A Preferred Units (162,109 units issued and outstanding at March 31, 2021 and December 31, 2020)	178,712	174,425
Common limited partner capital (6,206,021 and 6,110,092 units issued and outstanding at March 31, 2021 and December 31, 2020, respectively)	749,928	748,466
Total partners' capital	928,640	922,891
TOTAL LIABILITIES AND CAPITAL	$ 2,472,565	$ 2,499,817

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenues	$ 99,318	$ 104,903
Costs and expenses:
Cost of natural gas and NGLs	$ 20,476	$ 8,225
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 16,593	$ 21,811
General and administrative	10,344	16,561
Depreciation and amortization	28,511	29,666
Transaction costs		11
(Gain) loss on asset sales, net	(136)	115
Long-lived asset impairments	1,492	3,821
Total costs and expenses	77,280	80,210
Other income (expense), net	55	(427)
Interest expense	(13,953)	(23,828)
Loss on ECP Warrants and other	(1,481)	0
Income before income taxes and equity method investment income	6,659	438
Income tax benefit	14	13
Income from equity method investees	2,315	3,311
Net income	8,988	3,762
Net income (loss) attributable to limited partners	5,056	4,698
Net loss attributable to noncontrolling interest		1,881
Net income attributable to Summit Midstream Partners, LP	5,056	4,698
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners	(4,287)	(7,125)
Series A Preferred Units | Subsidiary
Costs and expenses:
Net income (loss) attributable to limited partners	(3,932)	(945)
Common Units
Costs and expenses:
Net income (loss) attributable to limited partners	$ 769	$ (2,427)
Net income (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.13	$ (0.80)
Diluted (in dollars per share)	$ 0.12	$ (0.80)
Weighted-average limited partner units outstanding:
Basic (shares)	6,125	3,021
Diluted (shares)	6,260	3,021
Gathering Services and Related Fees
Revenues:
Total revenues	$ 70,348	$ 83,792
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	20,763	13,780
Other Revenues
Revenues:
Total revenues	$ 8,207	$ 7,331

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Series A Preferred UnitsNoncontrolling Interest	Common Noncontrolling InterestNoncontrolling Interest	Partners' Capital	Partners' CapitalSeries A Preferred Units
Beginning balance at Dec. 31, 2019	$ 785,236	$ 293,616	$ 186,070	$ 305,550
Net income (loss)	2,817	7,125	(1,881)	(2,427)
Net cash distributions to SMLP unitholders	(6,037)		(6,037)
Unit-based compensation	2,723		2,723
Effect of common unit issuances under SMLP LTIP			2,322	(2,322)
Tax withholdings and associated payments on vested SMLP LTIP awards	(984)		(984)
Ending balance at Mar. 31, 2020	783,755	$ 300,741	$ 182,213	300,801
Beginning balance at Dec. 31, 2020	922,891			748,466	$ 174,425
Net income (loss)	5,056			769	4,287
Unit-based compensation	1,967			1,967
Tax withholdings and associated payments on vested SMLP LTIP awards	(1,274)			(1,274)
Ending balance at Mar. 31, 2021	$ 928,640			$ 749,928	$ 178,712

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 8,988	$ 3,762
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	28,746	29,900
Noncash lease expense	289	473
Amortization of debt issuance costs	1,717	1,582
Unit-based and noncash compensation	1,967	2,723
Income from equity method investees	(2,315)	(3,311)
Distributions from equity method investees	6,268	7,494
(Gain) loss on asset sales, net	(136)	115
Loss on ECP Warrants and other	1,481	0
Long-lived asset impairment	1,492	3,821
Changes in operating assets and liabilities:
Accounts receivable	7,592	18,470
Trade accounts payable	4,544	3,973
Accrued expenses	(1,546)	(138)
Deferred revenue, net	(576)	5,161
Ad valorem taxes payable	(1,497)	(4,781)
Accrued interest	504	3,059
Accrued environmental remediation, net	324	(17)
Other, net	(6,412)	(2,085)
Net cash provided by operating activities	51,430	70,201
Cash flows from investing activities:
Capital expenditures	(2,610)	(18,583)
Proceeds from asset sale	8,000	0
Other, net	0	217
Net cash used in investing activities	(229)	(76,399)
Cash flows from financing activities:
Net cash distributions to noncontrolling interest SMLP unitholders	0	(6,037)
Borrowings under Revolving Credit Facility	0	55,000
Repayments on Revolving Credit Facility	(55,000)	(34,000)
Repayments on SMPH Term Loan before TL Restructuring	0	(750)
Proceeds from issuance of Subsidiary Series A preferred units, net of issuance costs	0	33,946
Debt issuance costs	(4,909)	(101)
Proceeds from asset sale	143	0
Other, net	(179)	(1,401)
Net cash provided by (used in) financing activities	(42,445)	46,657
Net change in cash, cash equivalents and restricted cash	8,756	40,459
Cash, cash equivalents and restricted cash, beginning of period	15,544	36,922
Cash, cash equivalents and restricted cash, end of period	24,300	77,381
Permian Transmission Credit Facility [Member]
Cash flows from financing activities:
Borrowings under Revolving Credit Facility	17,500	0
Double E
Cash flows from investing activities:
Investment in Double E equity method investee	$ (5,619)	$ (58,033)

ORGANIZATION, BUSINESS OPERATIO

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION	3 Months Ended
	Mar. 31, 2021
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. 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 sponsor at that time, Energy Capital Partners II, LLC (“ECP”), to acquire Summit Investments, the parent company of the General Partner. The acquisition of Summit Investments resulted in the Partnership acquiring (a) 2.3 million SMLP common units (34.6 million SMLP common units prior to the Partnership’s 1-for-15 reverse unit split of its common units, effective November 9, 2020 (the “Reverse Unit Split”)) that were pledged as collateral under the SMPH Term Loan, (b) 0.7 million SMLP common units (10.7 million SMLP common units prior to the Reverse Unit Split) 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 (10.0 million SMLP common units prior to the Reverse Unit Split) (refer to Note 9 – Partners’ Capital and Mezzanine Capital for additional details). Pursuant to the Purchase Agreement, the Partnership assumed the 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 (16.6 million common units prior to the Reverse Unit Split) it acquired that were not pledged as collateral under the SMPH Term Loan. On November 17, 2020, the Partnership issued the 2.3 million SMLP common units (34.6 million common units prior to the Reverse Unit Split) that were pledged as collateral under the SMPH Term Loan as partial consideration for a consensual debt discharge and restructuring (the “TL Restructuring”) of its SMP Holdings’ $155.2 million term loan (“SMPH Term Loan”). SMP Holdings is a wholly-owned subsidiary of Summit Investments. 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. 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 condensed consolidated financial statements in accordance with GAAP as established by the FASB and pursuant to the rules and regulations of the SEC pertaining to interim financial information. The condensed consolidated financial statements contained in this report include all normal and recurring material adjustments that, in the opinion of management, are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented herein. 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 condensed consolidated financial statements contained in this report 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 COVID-19 pandemic 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 development and availability of treatments and vaccines and the extent to which these treatments and vaccines may remain effective as potential new strains of the coronavirus emerge. 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 ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP Except for the below, there have been no changes to the Partnership’s significant accounting policies since December 31, 2020. Cash, Cash Equivalents and Restricted Cash. We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. Cash that is held by a major bank and has restrictions on its availability to the Partnership is classified as restricted cash. The restricted cash balance of $8.1 million at March 31, 2021 is related to proceeds from the Permian Transmission Credit Facility, which can be used to finance Permian Transmission’s capital calls associated with its investment in Double E, for debt service or other general corporate purposes. See Note 7 - Debt for additional information. Interest Rate Swaps. Interest rate swap agreements are reported as either assets or liabilities on the consolidated balance sheet at fair value. Interest rate swap agreements are not designated as cash-flow hedges, and accordingly, the changes in the fair value are recorded in earnings. The Partnership does not use interest rate swap agreements for speculative purposes. New a . 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. 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

REVENUE	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
REVENUE	3. REVENUE Performance obligations. The following table presents estimated revenue expected to be recognized during the remainder of 2021 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated minimum volume commitments. 2021 2022 2023 2024 2025 Thereafter Gathering services and related fees $ 74,014 $ 84,215 $ 66,330 $ 49,872 $ 32,996 $ 22,078 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 15 – Segment Information. Three Months Ended March 31, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,572 $ — $ — $ 8,572 Williston Basin 12,633 12,227 4,506 29,366 DJ Basin 6,263 110 704 7,077 Permian Basin 2,199 6,518 116 8,833 Piceance Basin 24,784 1,853 1,177 27,814 Barnett Shale 9,696 55 1,061 10,812 Marcellus Shale 6,201 — — 6,201 Total reportable segments 70,348 20,763 7,564 98,675 All other segments — — 643 643 Total $ 70,348 $ 20,763 $ 8,207 $ 99,318 Three Months Ended March 31, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 6,962 $ — $ — $ 6,962 Williston Basin 23,797 4,324 3,142 31,263 DJ Basin 6,855 70 1,034 7,959 Permian Basin 2,311 4,512 187 7,010 Piceance Basin 27,189 1,003 1,065 29,257 Barnett Shale 10,443 3,871 1,260 15,574 Marcellus Shale 6,235 — — 6,235 Total reportable segments 83,792 13,780 6,688 104,260 All other segments — — 643 643 Total $ 83,792 $ 13,780 $ 7,331 $ 104,903 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: 2021 (In thousands) Contract assets, January 1, $ 2,026 Additions 2,840 Transfers out (973 ) Contract assets, March 31, $ 3,893 As of March 31, 2021, receivables with customers totaled $48.3 million and contract assets totaled $3.9 million and were included in the accounts receivable caption on the unaudited condensed consolidated balance sheets. 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 unaudited condensed consolidated balance sheets. 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 three months ended March 31, 2021 and 2020, the Partnership recognized $1.1 million and $2.4 million of gathering services and related fees, respectively, which were included in the contract liability balance as of the beginning of the period. See Note 6 – Deferred Revenue for additional details.

PROPERTY, PLANT, AND EQUIPMENT,

PROPERTY, PLANT, AND EQUIPMENT, NET	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT, NET	4. PROPERTY, PLANT AND EQUIPMENT, NET Details of the Partnership’s property, plant and equipment follows. March 31, 2021 December 31, 2020 (In thousands) Gathering and processing systems and related equipment $ 2,215,053 $ 2,213,501 Construction in progress 51,071 60,443 Land and line fill 10,440 10,440 Other 61,315 61,340 Total 2,337,879 2,345,724 Less: accumulated depreciation (549,657 ) (528,178 ) Property, plant and equipment, net $ 1,788,222 $ 1,817,546 Depreciation expense and capitalized interest for the Partnership follows. Three Months Ended March 31, 2021 2020 (In thousands) Depreciation expense $ 21,466 $ 21,698 Capitalized interest $ 1,060 $ 491

EQUITY METHOD INVESTMENTS

EQUITY METHOD INVESTMENTS	3 Months Ended
	Mar. 31, 2021
Equity Method Investments And Joint Ventures [Abstract]
EQUITY METHOD INVESTMENTS	5. EQUITY METHOD INVESTMENTS Double E. The Partnership is responsible for leading the development, permitting and construction of the Double E Project. During the three month periods ended March 31, 2021 and 2020, the Partnership made cash investments of $ 5.6 million and $58.0 million, respectively, in the Double E Project. Other than the investment activity noted above, Double E did not have any results of operations for the three months ended March 31, 2021, given that the Double E Project is currently under development. Ohio Gathering. As of March 31, 2021 and December 31, 2020, the Partnership’s ownership interest in Ohio Gathering was 38.0% and 38.2%, respectively. A reconciliation of the difference between the carrying amount of the Partnership’s interest in Ohio Gathering and the Partnership’s underlying investment per Ohio Gathering's books and records is provided in the table below as of March 31, 2021. 2021 (In thousands) Investment in Ohio Gathering, March 31, $ 256,430 March cash distributions 2,196 Basis difference 214,426 Investment in Ohio Gathering (Books and records), February 28, $ 473,052

DEFERRED REVENUE

DEFERRED REVENUE	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Contract With Customer Liability Disclosure [Text Block]	6. DEFERRED REVENUE A rollforward of current deferred revenue follows. Total (In thousands) Current deferred revenue, January 1, 2021 $ 9,988 Add: additions 1,273 Less: revenue recognized (1,244) Current deferred revenue, March 31, 2021 $ 10,017 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2021 $ 48,250 Add: additions 667 Less: reclassification to current deferred revenue (1,273) Noncurrent deferred revenue, March 31, 2021 $ 47,644

DEBT

DEBT	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
DEBT	7. DEBT Debt for the Partnership at March 31, 2021 and December 31, 2020, follows: March 31, 2021 December 31, 2020 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured Revolving Credit Facility due May 13, 2022 $ 802,000 $ 857,000 Permian Transmission Credit Facility : Permian Transmissions' variable rate senior secured Credit Facility due March 8, 2028 17,500 — Less: unamortized debt issuance costs (1) (5,105 ) — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 234,047 234,047 Less: unamortized debt issuance costs (1) (725 ) (859 ) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 15, 2025 259,463 259,463 Less: unamortized debt issuance costs (1) (2,262 ) (2,325 ) Total debt 1,304,918 1,347,326 Less: current portion — — Total long-term debt $ 1,304,918 $ 1,347,326 ( 1) Revolving Credit Facility. The Partnership’s wholly owned 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. The Revolving Credit Facility has a $1.1 billion borrowing capacity and matures on May 13, 2022. At March 31, 2021, the applicable margin under LIBOR borrowings was 2.75%, the interest rate was 2.86% and the unused portion of the Revolving Credit Facility totaled $275.9 million, subject to a commitment fee of 0.50%, after giving effect to the issuance of $22.1 million in outstanding but undrawn irrevocable standby letters of credit. Based on covenant limits, the Partnership’s available borrowing capacity under the Revolving Credit Facility as of March 31, 2021 was approximately $115.0 million. The Revolving Credit Facility includes three financial performance covenants which require 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 2.50 to 1.00, 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 3.50 to 1.00. As of and during the three months ended March 31, 2021, the Partnership was in compliance with the Revolving Credit Facility's financial covenants and there were no defaults or events of default. Permian Transmission Credit Facility. On March 8, 2021 (the “Closing Date”), the Partnership’s unrestricted subsidiary, Permian Transmission, entered into a Credit Agreement which allows for $175.0 million of senior secured credit facilities (the “Permian Transmission Credit Facilities”), including a $160.0 million Term Loan Facility (the “Term Loan Facility”) and a $15.0 million Working Capital Facility (the “Working Capital Facility”). The Permian Transmission Credit Facilities can be used to finance Permian Transmission’s capital calls associated with its investment in Double E, debt service and other general corporate purposes. Unexpended proceeds from draws on the Permian Transmission Credit Facilities are classified as restricted cash on the accompanying condensed consolidated balance sheets. The Permian Transmission Credit Facilities mature on the earlier of (i) the sixth anniversary of the term conversion date and (ii) seven years after the initial funding date, which occurred on the March 8, 2021. Loans under the Permian Transmission Credit Facilities are subject to varying rates of interest based on whether the loan is an Adjusted LIBOR borrowing (as defined in the credit agreement) or Alternate Base Rate (“ABR”) borrowing (as defined in the credit agreement). Adjusted LIBOR borrowings bear interest at (i) from the Closing Date to the fifth anniversary of the Closing Date, Adjusted LIBOR (as defined in the credit agreement) plus 2.375% and (ii) thereafter, Adjusted LIBOR plus 2.625%. ABR borrowings bear interest at (i) from the Closing Date to the fifth anniversary of the Closing Date, ABR (as defined in the credit agreement) plus 1.375% and (ii) thereafter, ABR plus 1.625%. The term conversion date will occur upon satisfaction of customary conditions, including bringing the Double E project into service pursuant to its transportation agreements. The Permian Transmission Credit Facilities include customary representations and warranties, affirmative covenants, negative covenants, and events of default with customary cure periods, knowledge qualifiers and materiality qualifiers. Events of default include non-payment of principal and interest, noncompliance with affirmative and negative covenants, inaccuracy of representations and warranties, not achieving term conversion by a specified date, termination of material contracts, revocation of material permits and other customary events of default. Permian Transmission is required to take all actions, within its control, to comply with any such covenants that apply to Double E. Secured interests in the equity and assets of Permian Transmission, including its 70% direct membership interest in Double E, have been pledged as collateral under the Credit Facilities. Upon term conversion, the Permian Transmission Credit Facilities will amortize based on a 10-year sculpted amortization schedule. Permian Transmission will also be required to maintain a 6-month debt service reserve, which can be supported by letters of credit issued under the Working Capital Facility. In addition, the Credit Facilities allow for restricted payments so long as there are no defaults or events of default, Permian Transmission maintains a 1.20x debt service coverage ratio and complies with the debt service reserve requirements and there is no breach of a material contract that would have a material adverse effect on distributions to Permian Transmission. As of March 31, 2021, the applicable margin under Adjusted LIBOR borrowings was 2.375%, the interest rate was 2.5% and the unused portion of the Permian Transmission Credit Facilities totaled $157.5 million, subject to a commitment fee of 0.70% as of March 31, 2021. Based on covenant limits, the Partnership’s available borrowing capacity under the Permian Transmission Credit Facilities, as of March 31, 2021, was approximately $155.5 million. As of and during the period from the Closing Date to March 31, 2021, the Partnership was in compliance with the Permian Transmission Credit Facilities financial covenants. There were no defaults or events of default during the period from the Closing Date to March 31, 2021. 2022 Senior Notes. 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. Summit Holdings and Finance Corp., the co-issuers of the 2022 Senior Notes (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 three month period ended March 31, 2021, that Partnership was in compliance with the financial covenants governing its 2022 Senior Notes. 2025 Senior Notes. 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. As of March 31, 2021, 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 three month period ended March 31, 2021, that Partnership was in compliance with the financial covenants governing its 2025 Senior Notes.

FINANCIAL INSTRUMENTS

FINANCIAL INSTRUMENTS	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
FINANCIAL INSTRUMENTS	8. FINANCIAL INSTRUMENTS Fair Value. A summary of the estimated fair value of our financial instruments follows. March 31, 2021 December 31, 2020 Carrying Value, Net Estimated fair value (Level 2) Carrying Value, Net Estimated fair value (Level 2) (in thousands) 2022 Senior Notes $ 233,322 $ 228,391 $ 233,188 $ 215,713 2025 Senior Notes 257,201 214,814 257,138 168,002 The balance sheet carrying values for the Revolving Credit Facility and the Permian Transmission Credit Facility Interest Rate Swaps. In connection with the 2021 establishment of the Permian Transmission Credit Facility, the Partnership entered into $161.5 million of notional amount interest rate swaps to manage its exposure to variability in expected cash flows attributable to interest rate risk. Interest rate swaps convert a portion of the Partnership’s variable rate debt to fixed rate debt. The Partnership chooses counterparties for its derivative instruments that it believes are creditworthy at the time the transactions are entered into, and the Partnership actively monitors the creditworthiness where applicable. However, there can be no assurance that a counterparty will be able to meet its obligations to the Partnership. The Partnership presents its derivative positions on a gross basis and does not net the asset and liability positions. As of March 31, 2021, the Partnership’s swap agreements had a fair value of less than $0.1 million and are recorded within Other assets on the condensed consolidated balance sheets.

PARTNERS' CAPITAL AND MEZZANINE

PARTNERS' CAPITAL AND MEZZANINE CAPITAL	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
PARTNERS' CAPITAL AND MEZZANINE CAPITAL	9. PARTNERS' CAPITAL AND MEZZANINE CAPITAL Common Units. A rollforward of the number of issued and outstanding common limited partner units follows for the period from December 31, 2020 to March 31, 2021. Common Units Units, December 31, 2020 6,110,092 Common units issued for SMLP LTIP, net 95,929 Units, March 31, 2021 6,206,021 Series A Preferred Units. In 2017, the Partnership issued 300,000 Series A Preferred Units at a price to the public of $1,000 per unit. As of March 31, 2021, the Partnership had 162,109 Series A Preferred Units outstanding On March 10, 2021, the Partnership commenced an offer to exchange its Series A Preferred Units for up to 2,160,000 (the “Maximum Exchange Amount”) newly issued common units (the “2021 Exchange Offer”), with each participating holder receiving 27 common units for each Series A Preferred Unit properly tendered (and not validly withdrawn) (the “Exchange Consideration”). On March 23, 2021, the Partnership announced an increase of the Exchange Consideration to 30 common units for each Series A Preferred Unit properly tendered (and not validly withdrawn), and a corresponding increase in the Maximum Exchange Amount to 2,400,000 newly issued common units. The 2021 Exchange Offer expired on April 13, 2021. As a result of the 2021 Exchange Offer, the Partnership exchanged 18,662 Series A Preferred Units at a ratio of 30 common units per Series A Preferred Unit for a total of 538,715 SMLP common units, net of units withheld for withholding taxes. Upon completion of the 2021 Exchange Offer on April 15, 2021, the Partnership has 143,447 Series A Preferred Units outstanding. Subsidiary Series A Preferred Units. 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. If the Partnership elects to make payment-in-kind (“PIK”) distributions to holders of its Subsidiary Series A Preferred Units, these PIK distributions increase the liquidation preference on each Subsidiary Series A Preferred Unit. Net Income (Loss) attributable to common limited partners includes adjustments for PIK distributions and redemption accretion. During the three months ended March 31, 2021, the Partnership elected to make PIK distributions and issued 1,494 Subsidiary Series A Preferred Units. As of March 31, 2021, the Partnership has 86,802 Subsidiary Series A Preferred Units issued and outstanding. If the Subsidiary Series A Preferred Units were redeemed on March 31, 2021, the redemption amount would be $108.5 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 our Subsidiary Series A Preferred Unit balance from January 1, 2021 to March 31, 2021: 2021 (in thousands) Balance at January 1, $ 89,658 PIK distributions 1,494 Redemption accretion 2,438 Balance at March 31, $ 93,590 Warrants. On May 28, 2020, and in connection with the GP Buy-In Transaction, the Partnership issued (i) a warrant to purchase up to 537,307 SMLP common units (8,059,609 SMLP common units prior to the Reverse Unit Split) to ECP NewCo (the “ECP NewCo Warrant”) and (ii) a warrant to purchase up to 129,360 SMLP common units (1,940,391 SMLP common units prior to the Reverse Unit Split) 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 $15.345 per SMLP common unit ($1.025 prior to the Reverse Unit Split) and the Partnership may issue a maximum of 666,667 SMLP common units (10,000,000 SMLP common units prior to the Reverse Unit Split) 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 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 payment of such cash would not result in any violation of any financial covenant under the Revolving Credit Facility, and 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 ($2.00 prior to the Reverse Unit Split) per SMLP common unit above the exercise price. At March 31, 2021, the ECP Warrants were valued at $3.4 million using the Black-Scholes model and accounted for as a liability instrument. 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. The Partnership’s last distribution was paid on February 14, 2020, to unitholders of record at the close of business on February 7, 2020.

EARNINGS PER UNIT

EARNINGS PER UNIT	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
EARNINGS PER UNIT	10. EARNINGS PER UNIT The following table details the components of EPU. Three Months Ended March 31, 2021 2020 (In thousands, except per-unit amounts) Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) $ 8,988 $ 3,762 Net (income) loss attributable to Subsidiary Series A Preferred Units (3,932 ) (945 ) Net loss attributable to noncontrolling interest — 1,881 Net income (loss) attributable to Summit Midstream Partners, LP 5,056 4,698 Less: Net income attributable to Series A Preferred Units (4,287 ) (7,125 ) Net income (loss) attributable to common limited partners $ 769 $ (2,427 ) Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 6,125 3,021 Effect of nonvested phantom units 135 — Weighted-average common units outstanding – diluted 6,260 3,021 Net Income (Loss) per limited partner unit: Common unit – basic $ 0.13 $ (0.80 ) Common unit – diluted $ 0.12 $ (0.80 ) Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 44 126

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
SUPPLEMENTAL CASH FLOW INFORMATION	11. SUPPLEMENTAL CASH FLOW INFORMATION Three Months Ended March 31, 2021 2020 (In thousands) Supplemental cash flow information: Cash interest paid $ 12,885 $ 19,660 Less: capitalized interest 1,060 491 Interest paid (net of capitalized interest) $ 11,825 $ 19,169 Cash paid for taxes $ — $ — Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 5,613 $ 13,765 Accretion of Subsidiary Series A Preferred Units 2,438 —

UNIT-BASED AND NONCASH COMPENSA

UNIT-BASED AND NONCASH COMPENSATION	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
UNIT-BASED AND NONCASH COMPENSATION	12. 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. Items to note: • During the quarterly period ended March 31, 2021, the Partnership granted 148,822 phantom units and associated distribution equivalent rights to employees in connection with the Partnership’s annual incentive compensation award cycle. These awards had a grant date fair value of $20.42 per common unit and vest ratably over a three-year • During the quarterly period ended March 31, 2021, the Partnership issued 40,002 common units to the Partnership’s six independent directors in connection with their annual compensation plan. These awards had a grant date fair value of $28.99 and vested immediately. • As of March 31, 2021, approximately 0.3 million common units remained available for future issuance under the SMLP LTIP.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	13. 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. A rollforward of the Partnership’s undiscounted accrued environmental remediation follows and is primarily related to the Meadowlark Rupture. Total (In thousands) Accrued environmental remediation, December 31, 2020 $ 2,929 Payments made (86 ) Additional accruals 410 Accrued environmental remediation, March 31, 2021 $ 3,253 As of March 31, 2021, 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 March 31, 2022. 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 July 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. 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 the Partnership 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.

RESTRUCTURING

RESTRUCTURING	3 Months Ended
	Mar. 31, 2021
Restructuring And Related Activities [Abstract]
RESTRUCTURING	14. 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, and during the quarterly period ended March 31, 2021, the Partnership expensed approximately $0.7 million of costs associated with these 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. At March 31, 2021, the Partnership has accrued and unpaid liabilities of $1.0 million associated with the 2020 Restructuring Activities. 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, and during the quarterly period ended March 31, 2020, the Partnership expensed approximately $2.8 million of costs associated with these 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. At March 31, 2021, the Partnership has accrued and unpaid liabilities of less than $0.1 million associated with the 2019 Restructuring Activities

SEGMENT INFORMATION

SEGMENT INFORMATION	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
SEGMENT INFORMATION	15. SEGMENT INFORMATION As of March 31, 2021, the Partnership’s reportable segments are: • the Utica Shale, which is served by Summit Utica; • Ohio Gathering, which includes our ownership interest in OGC and OCC; • the Williston Basin, which is served by Polar and Divide, 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. 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 the Partnership’s 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. For the three months ended March 31, 2021, other than the investment activity described in Note 5, 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 segment 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. March 31, 2021 December 31, 2020 (In thousands) Assets (1) Utica Shale $ 206,140 $ 209,425 Ohio Gathering 256,430 259,888 Williston Basin 413,390 425,873 DJ Basin 196,788 199,920 Permian Basin 168,759 165,765 Piceance Basin 565,002 579,800 Barnett Shale 332,326 336,629 Marcellus Shale 175,656 176,441 Total reportable segment assets 2,314,491 2,353,741 Corporate and Other 158,074 146,076 Total assets $ 2,472,565 $ 2,499,817 (1) At March 31, 2021, Corporate and Other included $138.0 million relating to our investment in Double E (included in the Investment in equity method investees caption of the unaudited condensed consolidated balance sheet). At December 31, 2020, Corporate and Other included $132.9 million relating to our investment in Double E. Segment adjusted EBITDA by reportable segment follows. Three Months Ended March 31, 2021 2020 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 7,719 $ 5,928 Ohio Gathering 6,872 7,939 Williston Basin 10,805 16,192 DJ Basin 5,347 5,911 Permian Basin 709 1,581 Piceance Basin 21,034 23,557 Barnett Shale 8,016 8,760 Marcellus Shale 5,602 5,320 Total of reportable segments' measures of profit $ 66,104 $ 75,188 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 follows. Three Months Ended March 31, 2021 2020 (In thousands) Reconciliation of income before income taxes and income from equity method investees to total of reportable segments' measures of profit: Income before income taxes and income from equity method investees $ 6,659 $ 438 Add: Corporate and Other expense 7,796 12,077 Interest expense 13,953 23,828 Depreciation and amortization (1) 28,746 29,900 Proportional adjusted EBITDA for equity method investees 6,872 7,939 Adjustments related to MVC shortfall payments — (5,442 ) Adjustments related to capital reimbursement activity (1,245 ) (211 ) Unit-based and noncash compensation 1,967 2,723 (Gain) loss on asset sales, net (136 ) 115 Long-lived asset impairment 1,492 3,821 Total of reportable segments' measures of profit $ 66,104 $ 75,188 (1)

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	16. SUBSEQUENT EVENTS Exchange Offer. On April 15, 2021, the Partnership completed the 2021 Exchange Offer and accepted for exchange 18,662 Series A Preferred Units for the issuance of 538,715 SMLP common units, net of units withheld for withholding taxes.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Presentation and Consolidation. The Partnership prepares its condensed consolidated financial statements in accordance with GAAP as established by the FASB and pursuant to the rules and regulations of the SEC pertaining to interim financial information. The condensed consolidated financial statements contained in this report include all normal and recurring material adjustments that, in the opinion of management, are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented herein. 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 condensed consolidated financial statements contained in this report 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.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash. We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. Cash that is held by a major bank and has restrictions on its availability to the Partnership is classified as restricted cash. The restricted cash balance of $8.1 million at March 31, 2021 is related to proceeds from the Permian Transmission Credit Facility, which can be used to finance Permian Transmission’s capital calls associated with its investment in Double E, for debt service or other general corporate purposes. See Note 7 - Debt for additional information.
Interest Rate Swaps	Interest Rate Swaps. Interest rate swap agreements are reported as either assets or liabilities on the consolidated balance sheet at fair value. Interest rate swap agreements are not designated as cash-flow hedges, and accordingly, the changes in the fair value are recorded in earnings. The Partnership does not use interest rate swap agreements for speculative purposes.
New Accounting Standards Recently Implemented	New a . 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. 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 (Tables)

REVENUE (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments	Performance obligations. The following table presents estimated revenue expected to be recognized during the remainder of 2021 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated minimum volume commitments. 2021 2022 2023 2024 2025 Thereafter Gathering services and related fees $ 74,014 $ 84,215 $ 66,330 $ 49,872 $ 32,996 $ 22,078
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 15 – Segment Information. Three Months Ended March 31, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,572 $ — $ — $ 8,572 Williston Basin 12,633 12,227 4,506 29,366 DJ Basin 6,263 110 704 7,077 Permian Basin 2,199 6,518 116 8,833 Piceance Basin 24,784 1,853 1,177 27,814 Barnett Shale 9,696 55 1,061 10,812 Marcellus Shale 6,201 — — 6,201 Total reportable segments 70,348 20,763 7,564 98,675 All other segments — — 643 643 Total $ 70,348 $ 20,763 $ 8,207 $ 99,318 Three Months Ended March 31, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 6,962 $ — $ — $ 6,962 Williston Basin 23,797 4,324 3,142 31,263 DJ Basin 6,855 70 1,034 7,959 Permian Basin 2,311 4,512 187 7,010 Piceance Basin 27,189 1,003 1,065 29,257 Barnett Shale 10,443 3,871 1,260 15,574 Marcellus Shale 6,235 — — 6,235 Total reportable segments 83,792 13,780 6,688 104,260 All other segments — — 643 643 Total $ 83,792 $ 13,780 $ 7,331 $ 104,903
Schedule of Information about Contract Assets from Contracts with Customers	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: 2021 (In thousands) Contract assets, January 1, $ 2,026 Additions 2,840 Transfers out (973 ) Contract assets, March 31, $ 3,893

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Schedule of property, plant, and equipment, net	Details of the Partnership’s property, plant and equipment follows. March 31, 2021 December 31, 2020 (In thousands) Gathering and processing systems and related equipment $ 2,215,053 $ 2,213,501 Construction in progress 51,071 60,443 Land and line fill 10,440 10,440 Other 61,315 61,340 Total 2,337,879 2,345,724 Less: accumulated depreciation (549,657 ) (528,178 ) Property, plant and equipment, net $ 1,788,222 $ 1,817,546
Schedule Of Depreciation Expense And Capitalized Interest Costs Table Text Block	Depreciation expense and capitalized interest for the Partnership follows. Three Months Ended March 31, 2021 2020 (In thousands) Depreciation expense $ 21,466 $ 21,698 Capitalized interest $ 1,060 $ 491

EQUITY METHOD INVESTMENTS (Tabl

EQUITY METHOD INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 2021
Equity Method Investments And Joint Ventures [Abstract]
Equity Method Investments	As of March 31, 2021 and December 31, 2020, the Partnership’s ownership interest in Ohio Gathering was 38.0% and 38.2%, respectively. A reconciliation of the difference between the carrying amount of the Partnership’s interest in Ohio Gathering and the Partnership’s underlying investment per Ohio Gathering's books and records is provided in the table below as of March 31, 2021. 2021 (In thousands) Investment in Ohio Gathering, March 31, $ 256,430 March cash distributions 2,196 Basis difference 214,426 Investment in Ohio Gathering (Books and records), February 28, $ 473,052

DEFERRED REVENUE (Tables)

DEFERRED REVENUE (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Rollforward of deferred revenue	A rollforward of current deferred revenue follows. Total (In thousands) Current deferred revenue, January 1, 2021 $ 9,988 Add: additions 1,273 Less: revenue recognized (1,244) Current deferred revenue, March 31, 2021 $ 10,017 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2021 $ 48,250 Add: additions 667 Less: reclassification to current deferred revenue (1,273) Noncurrent deferred revenue, March 31, 2021 $ 47,644

DEBT (Tables)

DEBT (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of debt and capital leases	Debt for the Partnership at March 31, 2021 and December 31, 2020, follows: March 31, 2021 December 31, 2020 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured Revolving Credit Facility due May 13, 2022 $ 802,000 $ 857,000 Permian Transmission Credit Facility : Permian Transmissions' variable rate senior secured Credit Facility due March 8, 2028 17,500 — Less: unamortized debt issuance costs (1) (5,105 ) — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 234,047 234,047 Less: unamortized debt issuance costs (1) (725 ) (859 ) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 15, 2025 259,463 259,463 Less: unamortized debt issuance costs (1) (2,262 ) (2,325 ) Total debt 1,304,918 1,347,326 Less: current portion — — Total long-term debt $ 1,304,918 $ 1,347,326 ( 1)

FINANCIAL INSTRUMENTS (Tables)

FINANCIAL INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Summary of the estimated fair value of debt instruments	A summary of the estimated fair value of our financial instruments follows.

PARTNERS' CAPITAL AND MEZZANI_2

PARTNERS' CAPITAL AND MEZZANINE CAPITAL (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of partner units activity	Common Units. A rollforward of the number of issued and outstanding common limited partner units follows for the period from December 31, 2020 to March 31, 2021. Common Units Units, December 31, 2020 6,110,092 Common units issued for SMLP LTIP, net 95,929 Units, March 31, 2021 6,206,021
Change in subsidiary	The following table shows the change in our Subsidiary Series A Preferred Unit balance from January 1, 2021 to March 31, 2021: 2021 (in thousands) Balance at January 1, $ 89,658 PIK distributions 1,494 Redemption accretion 2,438 Balance at March 31, $ 93,590

EARNINGS PER UNIT (Tables)

EARNINGS PER UNIT (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of earnings per limited partner unit	The following table details the components of EPU. Three Months Ended March 31, 2021 2020 (In thousands, except per-unit amounts) Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) $ 8,988 $ 3,762 Net (income) loss attributable to Subsidiary Series A Preferred Units (3,932 ) (945 ) Net loss attributable to noncontrolling interest — 1,881 Net income (loss) attributable to Summit Midstream Partners, LP 5,056 4,698 Less: Net income attributable to Series A Preferred Units (4,287 ) (7,125 ) Net income (loss) attributable to common limited partners $ 769 $ (2,427 ) Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 6,125 3,021 Effect of nonvested phantom units 135 — Weighted-average common units outstanding – diluted 6,260 3,021 Net Income (Loss) per limited partner unit: Common unit – basic $ 0.13 $ (0.80 ) Common unit – diluted $ 0.12 $ (0.80 ) Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 44 126

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Schedule of supplemental cash flow information	Three Months Ended March 31, 2021 2020 (In thousands) Supplemental cash flow information: Cash interest paid $ 12,885 $ 19,660 Less: capitalized interest 1,060 491 Interest paid (net of capitalized interest) $ 11,825 $ 19,169 Cash paid for taxes $ — $ — Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 5,613 $ 13,765 Accretion of Subsidiary Series A Preferred Units 2,438 —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Accrued Environmental Remediation	A rollforward of the Partnership’s undiscounted accrued environmental remediation follows and is primarily related to the Meadowlark Rupture. Total (In thousands) Accrued environmental remediation, December 31, 2020 $ 2,929 Payments made (86 ) Additional accruals 410 Accrued environmental remediation, March 31, 2021 $ 3,253

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of assets by reportable segment	Assets by reportable segment follow. March 31, 2021 December 31, 2020 (In thousands) Assets (1) Utica Shale $ 206,140 $ 209,425 Ohio Gathering 256,430 259,888 Williston Basin 413,390 425,873 DJ Basin 196,788 199,920 Permian Basin 168,759 165,765 Piceance Basin 565,002 579,800 Barnett Shale 332,326 336,629 Marcellus Shale 175,656 176,441 Total reportable segment assets 2,314,491 2,353,741 Corporate and Other 158,074 146,076 Total assets $ 2,472,565 $ 2,499,817 (1) At March 31, 2021, Corporate and Other included $138.0 million relating to our investment in Double E (included in the Investment in equity method investees caption of the unaudited condensed consolidated balance sheet). At December 31, 2020, Corporate and Other included $132.9 million relating to our investment in Double E.
Schedule of segment reporting information	Segment adjusted EBITDA by reportable segment follows. Three Months Ended March 31, 2021 2020 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 7,719 $ 5,928 Ohio Gathering 6,872 7,939 Williston Basin 10,805 16,192 DJ Basin 5,347 5,911 Permian Basin 709 1,581 Piceance Basin 21,034 23,557 Barnett Shale 8,016 8,760 Marcellus Shale 5,602 5,320 Total of reportable segments' measures of profit $ 66,104 $ 75,188
Reconciliation of net income to adjusted EBITDA	Segment adjusted EBITDA by reportable segment follows. 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 follows. Three Months Ended March 31, 2021 2020 (In thousands) Reconciliation of income before income taxes and income from equity method investees to total of reportable segments' measures of profit: Income before income taxes and income from equity method investees $ 6,659 $ 438 Add: Corporate and Other expense 7,796 12,077 Interest expense 13,953 23,828 Depreciation and amortization (1) 28,746 29,900 Proportional adjusted EBITDA for equity method investees 6,872 7,939 Adjustments related to MVC shortfall payments — (5,442 ) Adjustments related to capital reimbursement activity (1,245 ) (211 ) Unit-based and noncash compensation 1,967 2,723 (Gain) loss on asset sales, net (136 ) 115 Long-lived asset impairment 1,492 3,821 Total of reportable segments' measures of profit $ 66,104 $ 75,188 (1)

ORGANIZATION, BUSINESS OPERAT_2

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 28, 2020	Mar. 31, 2021	Dec. 31, 2020	Nov. 17, 2020
Organization And Business Operations [Line Items]
Purchase agreement date		May 28, 2020
Common limited partner capital (shares)		6,206,021	6,110,092
Common Units
Organization And Business Operations [Line Items]
Number of common units purchased.	537,307
Common Units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (shares)		400,000
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
Common Units Not Pledged As Collateral		700,000		34,600,000
Common units issued prior to reverse unit split		10,700,000
Common units retire		1,100,000
Summit Investments
Organization And Business Operations [Line Items]
Cash paid to Acquire investment		$ 35
Summit Investments | Common Units
Organization And Business Operations [Line Items]
Common units issued prior to reverse unit split		10,000,000
Number of common units purchased.		700,000
SMP Holdings
Organization And Business Operations [Line Items]
Debt discharge and restructuring		$ 155.2

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP - Cash, Cash Equivalents and Restricted Cash - Narrative (Details) $ in Thousands	Mar. 31, 2021USD ($)
Accounting Policies [Abstract]
Restricted cash	$ 8,067

REVENUE - Schedule of Estimated

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) - Gathering Services and Related Fees $ in Thousands	Mar. 31, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-04-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	9 months
Revenue, remaining performance obligation	$ 74,014
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	$ 22,078

REVENUE - Schedule of Disaggreg

REVENUE - Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenues	$ 99,318	$ 104,903
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	643	643
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	98,675	104,260
Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	8,572	6,962
Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	29,366	31,263
Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	7,077	7,959
Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	8,833	7,010
Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	27,814	29,257
Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	10,812	15,574
Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,201	6,235
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues	70,348	83,792
Gathering Services and Related Fees | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
Gathering Services and Related Fees | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	70,348	83,792
Gathering Services and Related Fees | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	8,572	6,962
Gathering Services and Related Fees | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	12,633	23,797
Gathering Services and Related Fees | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	6,263	6,855
Gathering Services and Related Fees | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	2,199	2,311
Gathering Services and Related Fees | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	24,784	27,189
Gathering Services and Related Fees | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	9,696	10,443
Gathering Services and Related Fees | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,201	6,235
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues	20,763	13,780
Natural Gas, NGLs and Condensate Sales | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
Natural Gas, NGLs and Condensate Sales | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	20,763	13,780
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	12,227	4,324
Natural Gas, NGLs and Condensate Sales | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	110	70
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	6,518	4,512
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	1,853	1,003
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	55	3,871
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	8,207	7,331
Other Revenues | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	643	643
Other Revenues | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	7,564	6,688
Other Revenues | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	0
Other Revenues | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,506	3,142
Other Revenues | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	704	1,034
Other Revenues | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	116	187
Other Revenues | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	1,177	1,065
Other Revenues | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	1,061	1,260
Other Revenues | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	$ 0	$ 0

REVENUE - Schedule of Informati

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Contract With Customer Asset And Liability [Abstract]
Contract assets, beginning of period	$ 2,026
Additions	2,840
Transfers out	(973)
Contract assets, end of period	$ 3,893

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenue From Contract With Customer [Line Items]
Receivables with customers	$ 48,300		$ 57,500
Contract assets included in accounts receivable	3,893		$ 2,026
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 1,100	$ 2,400

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,337,879	$ 2,345,724
Less: accumulated depreciation	(549,657)	(528,178)
Property, plant and equipment, net	1,788,222	1,817,546
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,215,053	2,213,501
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	51,071	60,443
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,440	10,440
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 61,315	$ 61,340

PROPERTY, PLANT, AND EQUIPMEN_4

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 21,466	$ 21,698
Capitalized interest	$ 1,060	$ 491

EQUITY METHOD INVESTMENTS - Nar

EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Additional cash investments	$ 5.6	$ 58
OGC | Principal Owner
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest	38.00%		38.20%

EQUITY METHOD INVESTMENTS - Rol

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, March 31,	$ 394,405	$ 394,405
March cash distributions		6,268	$ 7,494
Investment in Ohio Gathering (Books and records), February 28,		392,740
OGC | Summit Midstream Partners, LLC
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, March 31,	256,430	$ 256,430
March cash distributions	2,196
Basis difference	214,426
Investment in Ohio Gathering (Books and records), February 28,	$ 473,052

DEFERRED REVENUE - Rollforward

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 9,988
Current deferred revenue, Add: Additions	1,273
Current deferred revenue, Less revenue recognized	(1,244)
Current deferred revenue, ending balance	10,017
Noncurrent deferred revenue, beginning balance	48,250
Noncurrent deferred revenue, Additions	667
Noncurrent deferred revenue, Less reclassification to current deferred revenue	(1,273)
Noncurrent deferred revenue, ending balance	$ 47,644

DEBT - Components of Long-Term

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Long-term debt		$ 1,304,918	$ 1,347,326
Summit Midstream Partners Holdings L L C
Line of Credit Facility [Line Items]
Total debt		1,304,918	1,347,326
Less: current portion		0	0
Long-term debt		1,304,918	1,347,326
Summit Midstream Partners Holdings L L C | Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility		802,000	857,000
Summit Midstream Partners Holdings L L C | Permian Transmission Credit Facility [Member]
Line of Credit Facility [Line Items]
Secured notes		17,500	0
Less unamortized debt issuance costs	[1]	(5,105)	0
Summit Midstream Partners Holdings L L C | Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	[1]	(725)	(859)
Unsecured notes		234,047	234,047
Summit Midstream Partners Holdings L L C | Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	[1]	(2,262)	(2,325)
Unsecured notes		$ 259,463	$ 259,463
[1]	Issuance costs are being amortized over the life of the notes.

DEBT - Components of Long-Ter_2

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - Summit Midstream Partners Holdings L L C	Mar. 31, 2021	Dec. 31, 2020
Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Stated interest rate	5.75%	5.75%

DEBT - Revolving Credit Facilit

DEBT - Revolving Credit Facility (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
Line of Credit Facility [Line Items]
Borrowing capacity	$ 155,500
LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.625%
Revolving credit facility
Line of Credit Facility [Line Items]
Revolving credit facility maturity date	2022-05
Commitment fee on unused portion of the facility	0.50%
Interest rate at period end	2.86%
Unused portion under the facility	$ 275,900,000
Secured notes	22,100,000
Borrowing capacity	115,000,000
Revolving credit facility | Maximum
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,100,000,000
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	3.50
Revolving credit facility | Minimum [Member]
Line of Credit Facility [Line Items]
Ratio of consolidated trailing 12-month EBITDA to net interest expense	2.50
Revolving credit facility | LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.75%

DEBT - Permian Transmission Cre

DEBT - Permian Transmission Credit Facility (Narrative) (Details) - USD ($)	Mar. 08, 2021	Mar. 31, 2021
Line of Credit Facility [Line Items]
Proceeds from secured lines of credit	$ 175,000,000
Borrowing capacity		$ 155,500
Debt Default Long term Debt Amount		$ 0
LIBOR
Line of Credit Facility [Line Items]
Applicable margin		2.625%
Stated interest rate		2.50%
Debt instrument interest rate		0.70%
LIBOR | From and Including the Closing Date to and Excluding the Fifth Anniversary of the Closing Date
Line of Credit Facility [Line Items]
Applicable margin		2.375%
Unused portion of the Permian Transmission Credit facility		$ 157,500
Alternate base rate
Line of Credit Facility [Line Items]
Applicable margin		1.625%
Alternate base rate | From and Including the Closing Date to and Excluding the Fifth Anniversary of the Closing Date
Line of Credit Facility [Line Items]
Applicable margin		1.375%
Term Loan Credit Facility
Line of Credit Facility [Line Items]
Proceeds from secured lines of credit	160,000,000
Working Capital Credit Facility
Line of Credit Facility [Line Items]
Proceeds from secured lines of credit	$ 15,000,000

DEBT - Senior Notes (Narrative)

DEBT - Senior Notes (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
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%

FINANCIAL INSTRUMENTS - Fair va

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
2022 Senior Notes | Carrying Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 233,322	$ 233,188
2022 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	228,391	215,713
2025 Senior Notes | Carrying Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	257,201	257,138
2025 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 214,814	$ 168,002

FINANCIAL INSTRUMENTS - Narrati

FINANCIAL INSTRUMENTS - Narrative (Details) $ in Millions	Mar. 31, 2021USD ($)
Concentration Risk [Line Items]
Fair value, other assets	$ 0.1
Interest Rate Swap
Concentration Risk [Line Items]
Derivative liability, notional amount	$ 161.5

PARTNERS' CAPITAL AND MEZZANI_3

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Schedule of Units (Details) - Common Units	3 Months Ended
	Mar. 31, 2021shares
Rollforwards of the number of partner units
Units, beginning balance (in shares)	6,110,092
Common units issued for SMLP LTIP, net	95,929
Units, ending balance (in shares)	6,206,021

PARTNERS' CAPITAL AND MEZZANI_4

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	May 28, 2020	Mar. 31, 2021	Mar. 31, 2020	Apr. 15, 2021	Mar. 23, 2021	Mar. 10, 2021	Dec. 31, 2020	Dec. 31, 2017
Partners Capital [Line Items]
Preferred units issued		162,109					162,109
Common limited partner capital (in shares), outstanding		6,206,021					6,110,092
Common Units Issued					2,400,000	2,160,000
Number of Common Units						$ 27
Exchange Offer Expired Date		Apr. 13, 2021
Subsidiary Series A preferred unitholders, outstanding		162,109					162,109
Number of Common Units Exchanged		$ 30
Common Units Net of Units Withheld for Withholding Taxes		538,715
Maximum period following end of quarter to distribute all available cash		45 days
Common Units
Partners Capital [Line Items]
Number of common units purchased.	537,307
Exercise price of Warrants	$ 15.345		$ 1.025
Valuation of warrants		$ 3.4
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 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 payment of such cash would not result in any violation of any financial covenant under the Revolving Credit Facility, and 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.
Common Units | ECP Holdings Warrant
Partners Capital [Line Items]
Number of common units purchased.	129,360		1,940,391
Common Units | Energy Capital Partners
Partners Capital [Line Items]
Warrants exercisable date	May 28, 2023
Maximum | Common Units
Partners Capital [Line Items]
Common Units Issued	666,667		10,000,000
Exercise price of Warrants	$ 30		$ 2
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued		18,662						300,000
Interest in partnership per unit								$ 1,000
Common limited partner capital (in shares), outstanding		162,109
Redemption amount		$ 108.5
Series A Preferred Units | PIK [Member]
Partners Capital [Line Items]
Preferred units issued		1,494
Subsidiary Series A preferred unitholders, outstanding		86,802
Series A Preferred Units | Subsequent Event
Partners Capital [Line Items]
Subsidiary Series A preferred unitholders, outstanding				143,447

PARTNERS' CAPITAL AND MEZZANI_5

PARTNERS' CAPITAL AND MEZZANINE CAPITAL- Change in Subsidiary (Details) - Series A Preferred Units $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)shares
Partners Capital [Line Items]
Balance	$ 89,658
PIK distributions | shares	1,494
Redemption accretion	$ 2,438
Balance	$ 93,590

EARNINGS PER UNIT (Details)

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss)	$ 8,988	$ 3,762
Net income (loss) attributable to limited partners	$ 5,056	4,698
Net loss attributable to noncontrolling interest		$ 1,881
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	44	126
Series A Preferred Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ (4,287)	$ (7,125)
Series A Preferred Units | Subsidiaries
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	(3,932)	(945)
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ 769	$ (2,427)
Weighted-average common units outstanding – basic	6,125,000	3,021,000
Effect of nonvested phantom units	135
Weighted-average common units outstanding – diluted	6,260,000	3,021,000
Common unit – basic	$ 0.13	$ (0.80)
Common unit – diluted	$ 0.12	$ (0.80)

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION - Schedule of supplemental cash flow information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental cash flow information:
Cash interest paid	$ 12,885	$ 19,660
Less: capitalized interest	1,060	491
Interest paid (net of capitalized interest)	11,825	19,169
Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	5,613	$ 13,765
Series A Preferred Units
Noncash investing and financing activities:
Accretion of Subsidiary Series A Preferred Units	$ 2,438

UNIT-BASED AND NONCASH COMPEN_2

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) - SMLP LTIP	3 Months Ended
	Mar. 31, 2021Director$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units remaining available	300,000
Phantom Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted units (in shares)	148,822
Grant date fair value (in dollars per share) | $ / shares	$ 20.42
Vesting period	3 years
Issued units (in shares)	40,002
Number of Directors | Director	6
Grant date fair value (in dollars per share) | $ / shares	$ 28.99

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - Meadowlark Midstream Gathering System	3 Months Ended
	Mar. 31, 2021USD ($)
Loss Contingencies [Line Items]
Legal fines and other fees	$ 2,500,000
Accrued loss contingency	17,000,000
Maximum | Principal Owner
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy	25,000,000
Coverage from property and business interruption insurance policy	$ 200,000,000

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 2,929
Payments made	(86)
Additional accruals	410
Accrued environmental remediation, ending balance	$ 3,253

RESTRUCTURING - Additional info

RESTRUCTURING - Additional information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Accrued expenses	$ 11,666,000	$ 13,036,000
Accrued and unpaid liabilities	11,666,000	$ 13,036,000
2020 Restructuring Activities
Restructuring Cost And Reserve [Line Items]
Restructuring costs	700,000
2020 Restructuring Activities | Maximum
Restructuring Cost And Reserve [Line Items]
Accrued expenses	1,000,000
Accrued and unpaid liabilities	1,000,000
2019 Restructuring Activities
Restructuring Cost And Reserve [Line Items]
Restructuring costs	2,800,000
2019 Restructuring Activities | Maximum
Restructuring Cost And Reserve [Line Items]
Accrued expenses	100,000
Accrued and unpaid liabilities	$ 100,000

SEGMENT INFORMATION - Assets, R

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 2,472,565	$ 2,499,817
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,314,491	2,353,741
Reportable Segments | Utica Shale
Segment Reporting Information [Line Items]
Assets	206,140	209,425
Reportable Segments | Ohio Gathering
Segment Reporting Information [Line Items]
Assets	256,430	259,888
Reportable Segments | Williston Basin
Segment Reporting Information [Line Items]
Assets	413,390	425,873
Reportable Segments | DJ Basin
Segment Reporting Information [Line Items]
Assets	196,788	199,920
Reportable Segments | Permian Basin
Segment Reporting Information [Line Items]
Assets	168,759	165,765
Reportable Segments | Piceance Basin
Segment Reporting Information [Line Items]
Assets	565,002	579,800
Reportable Segments | Barnett Shale
Segment Reporting Information [Line Items]
Assets	332,326	336,629
Reportable Segments | Marcellus Shale
Segment Reporting Information [Line Items]
Assets	175,656	176,441
Corporate and Other
Segment Reporting Information [Line Items]
Assets	$ 158,074	$ 146,076

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Equity method investment	$ 394,405	$ 392,740
Corporate and Other | Double E
Segment Reporting Information [Line Items]
Capital expenditures	$ 138,000
Equity method investment		$ 132,900

SEGMENT INFORMATION - Adjusted

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 66,104	$ 75,188
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	7,719	5,928
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,872	7,939
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,805	16,192
DJ Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	5,347	5,911
Permian Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	709	1,581
Piceance Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	21,034	23,557
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	8,016	8,760
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 5,602	$ 5,320

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Net Income (Loss) to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting [Abstract]
Income before income taxes and equity method investment income	$ 6,659	$ 438
Add:
Corporate and Other expense	7,796	12,077
Interest expense	13,953	23,828
Depreciation and amortization	28,746	29,900
Proportional adjusted EBITDA for equity method investees	6,872	7,939
Adjustments related to MVC shortfall payments		(5,442)
Adjustments related to capital reimbursement activity	(1,245)	(211)
Unit-based and noncash compensation	1,967	2,723
(Gain) loss on asset sales, net	(136)	115
Long-lived asset impairment	1,492	3,821
Total of reportable segments' measures of profit	$ 66,104	$ 75,188

SUBSEQUENT EVENTS - Narrative (

SUBSEQUENT EVENTS - Narrative (Details) - shares	Apr. 15, 2021	Mar. 23, 2021	Mar. 10, 2021
Subsequent Event [Line Items]
Common units issued in exchange		2,400,000	2,160,000
Conversion of preferred stock to common stock [Member] | Subsequent Event
Subsequent Event [Line Items]
Common units issued in exchange	538,715
Series A Preferred Units | Conversion of preferred stock to common stock [Member] | Subsequent Event
Subsequent Event [Line Items]
Series A Preferred Units accepted for exchange	18,662