Summit Midstream Partners (SMLP) 10-Q 5 Nov 21 2021 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-35666
Entity Registrant Name	Summit Midstream Partners, LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-5200503
Entity Address, Address Line One	910 Louisiana Street
Entity Address, Address Line Two	Suite 4200
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	832
Local Phone Number	413-4770
Title of 12(b) Security	Common Units
Trading Symbol	SMLP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		7,169,834
Entity Central Index Key	0001549922
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
ASSETS
Cash and cash equivalents	$ 5,505	$ 15,544
Restricted cash	756	0
Accounts receivable, net	68,473	61,932
Other current assets	11,388	4,623
Total current assets	86,122	82,099
Property, plant and equipment, net	1,748,174	1,817,546
Intangible assets, net	180,017	199,566
Investment in equity method investees	481,985	392,740
Other noncurrent assets	4,379	7,866
TOTAL ASSETS	2,500,677	2,499,817
LIABILITIES AND CAPITAL
Trade accounts payable	10,706	11,878
Accrued expenses	15,369	13,036
Deferred revenue	10,576	9,988
Ad valorem taxes payable	6,531	9,086
Accrued compensation and employee benefits	7,981	9,658
Accrued interest	8,592	8,007
Accrued environmental remediation	2,684	1,392
Other current liabilities	10,098	5,363
Total current liabilities	72,537	68,408
Long-term debt	1,318,078	1,347,326
Noncurrent deferred revenue	43,248	48,250
Noncurrent accrued environmental remediation	2,924	1,537
Other noncurrent liabilities	37,860	21,747
Total liabilities	1,474,647	1,487,268
Commitments and contingencies (Note 14)
Mezzanine Capital
Subsidiary Series A Preferred Units (89,866 and 85,308 units issued and outstanding at September 30, 2021 and December 31, 2020, respectively)	101,932	89,658
Partners' Capital
Series A Preferred Units (143,447 and 162,109 units issued and outstanding at September 30, 2021 and December 31, 2020, respectively)	165,823	174,425
Common limited partner capital (7,169,834 and 6,110,092 units issued and outstanding at September 30, 2021 and December 31, 2020, respectively)	758,275	748,466
Total partners' capital	924,098	922,891
TOTAL LIABILITIES AND CAPITAL	$ 2,500,677	$ 2,499,817

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2021	Dec. 31, 2020
Partners' Capital
Common limited partner capital (in shares), issued	7,169,834	6,110,092
Common limited partner capital (in shares), outstanding	7,169,834	6,110,092
Subsidiary Series A Preferred Units
Subsidiary Series A preferred unitholders, issued (in shares)	89,866,000	85,308,000
Preferred units, outstanding (in shares)	89,866,000	85,308,000
Series A Preferred Units
Subsidiary Series A preferred unitholders, issued (in shares)	143,447	162,109
Preferred units, outstanding (in shares)	143,447	162,109

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Total revenues	$ 102,045	$ 90,153	$ 301,404	$ 287,063
Costs and expenses:
Type of Cost, Good or Service [Extensible List]			Natural Gas Liquids [Member]
Cost of natural gas and NGLs	21,072	8,632	$ 58,174	22,945
Operation and maintenance	20,781	22,168	54,881	65,131
General and administrative	8,477	10,561	48,414	39,908
Depreciation and amortization	30,992	29,505	87,866	88,801
Transaction costs	1,060	726	1,276	1,944
Gain on asset sales, net	(212)	(104)	(352)	(270)
Long-lived asset impairments	248	0	1,773	4,475
Total costs and expenses	82,418	71,488	252,032	222,934
Other income (expense), net	753	795	(1,532)	644
Loss on ECP Warrants	0	0	(13,634)	0
Interest expense	(15,530)	(19,018)	(44,985)	(64,836)
Gain on early extinguishment of debt	0	24,690	0	78,925
Income (loss) before income taxes and equity method investment income	4,850	25,132	(10,779)	78,862
Income tax benefit (expense)	79	(298)	341	104
Income from equity method investees	2,075	795	6,694	7,146
Net income (loss)	7,004	25,629	(3,744)	86,112
Add: deemed contribution from Preferred Exchange Offer	0	54,945	8,326	54,945
Net loss attributable to noncontrolling interest	0	0	0	3,274
Net income (loss) attributable to Summit Midstream Partners, LP	$ 2,751	$ 18,331	$ (16,018)	$ 79,746
Net income (loss) per limited partner unit:
Common unit - basic (in dollars per share)	$ (0.17)	$ 19.28	$ (2.99)	$ 36.12
Common unit - diluted (in dollars per share)	$ (0.17)	$ 18.67	$ (2.99)	$ 35.04
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners	$ (3,916)	$ (6,481)	$ (12,052)	$ (20,731)
Series A Preferred Units | Subsidiary
Costs and expenses:
Net income (loss) attributable to limited partners	(4,253)	(7,298)	(12,274)	(9,640)
Common Units
Costs and expenses:
Net income (loss) attributable to limited partners	$ (1,165)	$ 66,795	$ (19,744)	$ 113,960
Weighted-average limited partner units outstanding:
Common units - basic (in shares)	6,999	3,465	6,596	3,155
Common units - diluted (in shares)	6,999	3,577	6,596	3,252
Gathering services and related fees
Revenues:
Total revenues	$ 70,924	$ 71,964	$ 215,504	$ 229,667
Natural gas, NGLs and condensate sales
Revenues:
Total revenues	22,121	10,783	59,301	35,246
Other revenues
Revenues:
Total revenues	$ 9,000	$ 7,406	$ 26,599	$ 22,150

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Series A Preferred StockNoncontrolling Interest	Common Noncontrolling InterestNoncontrolling Interest	Partners' Capital	Partners' CapitalSeries A Preferred Stock
Beginning balance at Dec. 31, 2019	$ 785,236	$ 293,616	$ 186,070	$ 305,550	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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	0		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	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	55,324	4,750	(1,393)	49,592	2,375
Unit-based compensation	1,846		1,331	515
Tax withholdings and associated payments on vested SMLP LTIP awards	(62)		(34)	(28)
GP Buy-In Transaction assumption of noncontrolling interest in SMLP	0	(305,491)	(182,117)	182,117	305,491
Repurchase of common units under GP Buy-In Transaction	(44,078)			(44,078)
Other	(61)			(61)
Ending balance at Jun. 30, 2020	796,724	0	0	488,858	307,866
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	18,331			11,850	6,481
Unit-based compensation	1,622			1,622
Tax withholdings and associated payments on vested SMLP LTIP awards	(117)			(117)
Tax withholdings on Preferred Unit Exchange	(237)			(237)
Conversion of Preferred Units	0			64,996	(64,996)
Other	312			312
Ending balance at Sep. 30, 2020	816,635	0	0	567,284	249,351
Beginning balance at Dec. 31, 2020	922,891	0	0	748,466	174,425
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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	0	0	749,928	178,712
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(23,827)			(27,676)	3,849
Unit-based compensation	1,048			1,048
Tax withholdings and associated payments on vested SMLP LTIP awards	(98)			(98)
Tax withholdings on Preferred Unit Exchange	(465)			(465)
Conversion of Preferred Units	0			20,654	(20,654)
Ending balance at Jun. 30, 2021	905,298	0	0	743,391	161,907
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,751			(1,165)	3,916
Unit-based compensation	868			868
Tax withholdings and associated payments on vested SMLP LTIP awards	(361)			(361)
Tax withholdings on Preferred Unit Exchange	15,542			15,542
Ending balance at Sep. 30, 2021	$ 924,098	$ 0	$ 0	$ 758,275	$ 165,823

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL (Parenthetical) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Partners' Capital [Abstract]
Deemed contribution to common unit holders	$ 0	$ 8,300	$ 54,945	$ 8,326	$ 54,945

UNAUDITED CONDENSED CONSOLIDA_6

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income (loss)	$ (3,744)	$ 86,112
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	88,570	89,505
Noncash lease expense	793	1,925
Amortization of debt issuance costs	5,176	4,870
Unit-based and noncash compensation	3,883	6,191
Income from equity method investees	(6,694)	(7,146)
Distributions from equity method investees	20,004	19,859
Gain on asset sales, net	(352)	(270)
Gain on extinguishment of debt	0	(78,925)
Gain (loss) on ECP Warrants and other	13,635	(838)
Unrealized loss on interest rate swaps	(1,939)	0
Long-lived asset impairments	1,773	4,475
Changes in operating assets and liabilities:
Accounts receivable	(6,531)	20,922
Trade accounts payable	197	470
Accrued expenses	1,129	(1,078)
Deferred revenue, net	(4,413)	7,379
Ad valorem taxes payable	(2,555)	(1,546)
Accrued interest	585	2,680
Accrued environmental remediation, net	1,946	(1,368)
Other, net	16,268	(6,410)
Net cash provided by operating activities	127,731	146,807
Cash flows from investing activities:
Capital expenditures	(11,780)	(35,312)
Proceeds from asset sale	8,000	0
Investment in Double E equity method investee	(102,109)	(92,072)
Other, net	0	2,486
Net cash used in investing activities	(105,889)	(124,898)
Cash flows from financing activities:
Net cash distributions to noncontrolling interest SMLP unitholders	0	(6,037)
Borrowings under Credit Facilities		165,500
Repayments on Revolving Credit Facility	(132,000)	(34,000)
Repayments on SMPH Term Loan	0	(6,300)
Repurchase of Senior Notes	0	(82,844)
Tender Offers of Senior Notes	0	(48,712)
Proceeds from issuance of Subsidiary Series A Preferred Units, net of issuance costs	0	48,710
Borrowings under ECP loans	0	35,000
Repayment of ECP loans	0	(35,000)
Purchase of common units in GP Buy-In Transaction	0	(41,778)
Debt issuance costs	(5,179)	(835)
Proceeds from asset sale	357	288
Other, net	(1,303)	(2,527)
Net cash provided by (used in) financing activities	(31,125)	(8,535)
Net change in cash, cash equivalents and restricted cash	(9,283)	13,374
Cash, cash equivalents and restricted cash, beginning of period	15,544	36,922
Cash, cash equivalents and restricted cash, end of period	6,261	$ 50,296
Borrowings under Permian Transmission Credit Facility
Cash flows from financing activities:
Borrowings under Credit Facilities	$ 107,000

ORGANIZATION, BUSINESS OPERATIO

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION	9 Months Ended
	Sep. 30, 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 primarily 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 (5.7 million SMLP common units prior to the Reverse Unit Split). 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 10 – 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 (see "2015 Blacktail Release" in Note 14 - Commitments and Contingencies for additional information). 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 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. These unaudited condensed consolidated financial statements and notes thereto should be read in conjunction with the consolidated financial statements and related notes that are included in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2020. 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 continues to closely monitor 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. Going Concern Assessment. The accompanying unaudited condensed consolidated financial statements are prepared in accordance with GAAP applicable to a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. At the reporting date of the Partnership’s unaudited interim financial statements for the quarterly period ended June 30, 2021, the Partnership concluded that substantial doubt about the Partnership’s ability to continue as a going concern existed because of a lack of sufficient available liquidity to repay Summit Holdings’ obligations under its Revolving Credit Facility. On November 2, 2021, the Co-Issuers (as defined below) issued $700.0 million of 8.500% Senior Secured Second Lien Notes (“2026 Secured Notes”) and Summit Holdings concurrently entered into a new $400.0 million asset-based revolving credit facility (“ABL Facility”). See Note - 17 Subsequent Events for additional information. A portion of the proceeds from the issuance of the 2026 Secured Notes, together with cash on hand and borrowings under the ABL Facility, was used to repay, in full, the obligations under the Revolving Credit Facility and will be used to redeem all of the 2022 Senior Notes and pay the accrued and unpaid interest. The Partnership concluded that these actions resolved the substantial doubt that existed at the reporting date of the Partnership’s unaudited interim financial statements for the quarterly period ended June 30, 2021.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP	9 Months Ended
	Sep. 30, 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 below, there have been no changes to the Partnership’s significant accounting policies since December 31, 2020. Cash, Cash Equivalents and Restricted Cash. The Partnership considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. 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 $0.8 million at September 30, 2021 is related to proceeds from the Permian Transmission Credit Facility, which is available 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 ccounting standards recently implemented . 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. 2020-6 Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815 – 40) (“ASU 2020-6”). ASU 2020-6 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 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 2020-6 to determine its impact on the Partnership’s consolidated financial statements and disclosures. ASU No. 2020-4 Reference Rate Reform (“ASU 2020-4”). ASU 2020-4 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 2020-4 are effective as of March 12, 2020 through December 31, 2022. The Partnership is currently evaluating the provisions of ASU 2020-4 to determine its impact on the Partnership’s consolidated financial statements and disclosures.

REVENUE

REVENUE	9 Months Ended
	Sep. 30, 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 $ 21,192 $ 80,064 $ 62,179 $ 51,645 $ 35,200 $ 21,071 Revenue by Category. In the following tables, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 16 – Segment Information. Three Months Ended September 30, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 9,170 $ — $ — $ 9,170 Williston Basin 12,894 12,692 4,620 30,206 DJ Basin 6,180 153 644 6,977 Permian Basin 1,879 7,925 117 9,921 Piceance Basin 24,104 1,166 1,114 26,384 Barnett Shale 10,162 185 1,577 11,924 Marcellus Shale 6,535 — — 6,535 Total reportable segments 70,924 22,121 8,072 101,117 Corporate and Other — — 928 928 Total $ 70,924 $ 22,121 $ 9,000 $ 102,045 Nine Months Ended September 30, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 29,090 $ — $ — $ 29,090 Williston Basin 38,043 33,120 13,369 84,532 DJ Basin 18,334 568 3,204 22,106 Permian Basin 6,340 21,318 354 28,012 Piceance Basin 74,415 4,044 3,523 81,982 Barnett Shale 29,934 251 3,649 33,834 Marcellus Shale 19,348 — — 19,348 Total reportable segments 215,504 59,301 24,099 298,904 Corporate and Other — — 2,500 2,500 Total $ 215,504 $ 59,301 $ 26,599 $ 301,404 Three Months Ended September 30, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,385 $ — $ — $ 8,385 Williston Basin 10,941 4,958 3,136 19,035 DJ Basin 6,051 17 826 6,894 Permian Basin 2,595 4,803 168 7,566 Piceance Basin 26,576 528 1,233 28,337 Barnett Shale 10,545 477 1,399 12,421 Marcellus Shale 6,871 — — 6,871 Total reportable segments 71,964 10,783 6,762 89,509 Corporate and Other — — 644 644 Total $ 71,964 $ 10,783 $ 7,406 $ 90,153 Nine Months Ended September 30, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 26,885 $ — $ — $ 26,885 Williston Basin 47,145 12,413 9,054 68,612 DJ Basin 18,134 158 2,853 21,145 Permian Basin 7,617 13,537 481 21,635 Piceance Basin 79,987 1,932 3,394 85,313 Barnett Shale 30,865 7,206 4,437 42,508 Marcellus Shale 19,034 — — 19,034 Total reportable segments 229,667 35,246 20,219 285,132 Corporate and Other — — 1,931 1,931 Total $ 229,667 $ 35,246 $ 22,150 $ 287,063 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: Total (In thousands) Contract assets, December 31, 2020 $ 2,026 Additions 7,130 Transfers out (973) Contract assets, September 30, 2021 $ 8,183 As of September 30, 2021, receivables with customers totaled $56.1 million and contract assets totaled $8.2 million and are 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 are 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 September 30, 2021 and 2020, the Partnership recognized $2.3 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. For the nine months ended September 30, 2021 and 2020, the Partnership recognized $5.6 million and $7.1 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	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT	4. PROPERTY, PLANT AND EQUIPMENT Details of the Partnership’s property, plant and equipment follows. September 30, 2021 December 31, 2020 (In thousands) Gathering and processing systems and related equipment $ 2,220,218 $ 2,213,501 Construction in progress 49,781 60,443 Land and line fill 10,440 10,440 Other 59,287 61,340 Total 2,339,726 2,345,724 Less: accumulated depreciation (591,552) (528,178) Property, plant and equipment, net $ 1,748,174 $ 1,817,546 Depreciation expense and capitalized interest for the Partnership follows. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Depreciation expense $ 23,867 $ 21,537 $ 66,651 $ 64,899 Capitalized interest 85 1,449 395 2,268

EQUITY METHOD INVESTMENTS

EQUITY METHOD INVESTMENTS	9 Months Ended
	Sep. 30, 2021
Equity Method Investments and Joint Ventures [Abstract]
EQUITY METHOD INVESTMENTS	5. EQUITY METHOD INVESTMENTS The Partnership has equity method investments in Double E and Ohio Gathering, the balances of which are included in the Investment in equity method investees caption on the unaudited condensed consolidated balance sheets. Details of the Partnership’s equity method investments follows. September 30, 2021 December 31, 2020 (In thousands) Double E $ 233,612 $ 132,852 Ohio Gathering 248,373 259,888 Total $ 481,985 $ 392,740 Double E. The Partnership is responsible for leading the development, permitting and construction of the Double E Project. During the nine month periods ended September 30, 2021 and 2020, the Partnership made cash investments of $102.1 million and $92.1 million, respectively, in the Double E Project which included $2.5 million and $1.4 million of capitalized interest respectively. Other than the investment activity noted above, Double E did not have any results of operations for the nine months ended September 30, 2021, given that the Double E Project is currently under development. Ohio Gathering. As of September 30, 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 September 30, 2021: 2021 (In thousands) Investment in Ohio Gathering, September 30, $ 248,373 September cash distributions 2,163 Basis difference 210,093 Investment in Ohio Gathering (Books and records), August 31, $ 460,629

DEFERRED REVENUE

DEFERRED REVENUE	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
DEFERRED REVENUE	6. DEFERRED REVENUE Certain of the Partnership’s gathering and/or processing agreements provide for monthly or annual MVCs. The amount of the shortfall payment is based on the difference between the actual throughput volume shipped and/or processed for the applicable period and the MVC for the applicable period, multiplied by the applicable gathering or processing fee. Many of the Partnership’s gas gathering agreements contain provisions that can reduce or delay the cash flows that it expects to receive from MVCs to the extent that a customer's actual throughput volumes are above or below its MVC for the applicable contracted measurement period. A rollforward of current deferred revenue follows. Total (In thousands) Current deferred revenue, January 1, 2021 $ 9,988 Add: additions 5,606 Less: revenue recognized (5,018) Current deferred revenue, September 30, 2021 $ 10,576 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2021 $ 48,250 Add: additions 632 Less: reclassification to current deferred revenue (5,634) Noncurrent deferred revenue, September 30, 2021 $ 43,248

DEBT

DEBT	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
DEBT	7. DEBT Debt for the Partnership at September 30, 2021 and December 31, 2020, follows: September 30, 2021 December 31, 2020 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured revolving credit facility due May 13, 2022 (1) $ 725,000 $ 857,000 Permian Transmission Credit Facility : Permian Transmission's variable rate senior secured credit facility due March 8, 2028 107,000 — Less: unamortized debt issuance costs (4,936) — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 (2) 234,047 234,047 Less: unamortized debt issuance costs (497) (859) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 15, 2025 259,463 259,463 Less: unamortized debt issuance costs (1,999) (2,325) Total long-term debt $ 1,318,078 $ 1,347,326 (1) The Revolving Credit Facility was repaid in full on November 2, 2021 upon the issuance of the 2026 Secured Notes, and is therefore classified as non-current on the balance sheet. See Note 17 - Subsequent Events for additional information. (2) The indenture governing the 2022 Senior Notes was satisfied and discharged as of November 2, 2021 upon the issuance of the 2026 Secured Notes. The Co-Issuers delivered a notice of conditional redemption irrevocably calling for the redemption of all of the outstanding 2022 Senior Notes on November 12, 2021 and the Co-Issuers have irrevocably deposited with the trustee of the 2022 Senior Notes sufficient funds to redeem the 2022 Senior Notes in full on November 12, 2021. Therefore, the amounts are classified as non-current on the balance sheet. See Note 17 - Subsequent Events for additional information. Revolving Credit Facility. As of September 30, 2021, the Partnership’s wholly owned subsidiary, Summit Holdings, had a Revolving Credit Facility which allowed for revolving loans, letters of credit and swingline loans. As of September 30, 2021, the Revolving Credit Facility had $1.1 billion of commitments from lenders and was scheduled to mature on May 13, 2022. At September 30, 2021, the applicable margin for LIBOR borrowings was 3.25%, the interest rate was 3.34% and the unused portion of the Revolving Credit Facility totaled $351.1 million, subject to a commitment fee of 0.50%, after giving effect to the issuance of $23.9 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 September 30, 2021 was approximately $170.5 million. At September 30, 2021, the Revolving Credit Facility included three financial performance covenants which required 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 nine months ended September 30, 2021, the Partnership was in compliance with the Revolving Credit Facility's financial covenants, including the financial performance covenants, and there were no defaults or events of default. On November 2, 2021, a portion of the proceeds from the issuance of the 2026 Secured Notes, together with cash on hand and borrowings under the ABL Facility, was used to repay, in full, the obligations under the Revolving Credit Facility. See Note 17 - Subsequent Events for additional information. Permian Transmission Credit Facility. On March 8, 2021 (the “Permian 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 and a $15.0 million 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 unaudited condensed consolidated balance sheets. As of September 30, 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 $66.0 million, subject to a commitment fee of 0.7% after giving effect to the issuance of $2.0 million in outstanding but undrawn irrevocable standby letters of credit. As of and during the period from the Permian Closing Date to September 30, 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 Permian Closing Date to September 30, 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, unsecured 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. As of and during the nine month period ended September 30, 2021, the Partnership was in compliance with the financial covenants governing the 2022 Senior Notes. The Co-Issuers delivered a notice of conditional redemption irrevocably calling for the redemption on November 12, 2021 (the “Redemption Date”) of all of the outstanding 2022 Senior Notes at a redemption price equal to 100.0% of the principal amount of the 2022 Senior Notes to be redeemed, plus accrued and unpaid interest, if any, on the 2022 Senior Notes to be redeemed on the Redemption Date. In connection with the issuance of the 2026 Secured Notes, on November 2, 2021, the Co-Issuers irrevocably deposited with the trustee under the indenture governing the 2022 Senior Notes sufficient cash to redeem all of the 2022 Senior Notes, including the payment of all accrued and unpaid interest and all other amounts owing under the indenture governing the 2022 Senior Notes, and the indenture governing the 2022 Senior Notes was satisfied and discharged . See Note 17 - Subsequent Events for additional information. 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 unsecured 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 September 30, 2021, the Co-Issuers have the right to 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 nine month period ended September 30, 2021, the Partnership was in compliance with the financial covenants governing its 2025 Senior Notes. 8. LIABILITY MANAGEMENT TRANSACTIONS During the three and nine months ended September 30, 2020, the Partnership completed several liability management transactions, described below, that resulted in the early extinguishment of $210.8 million of the Partnership’s 2022 and 2025 Senior Notes during the nine months ended September 30, 2020. Open Market Repurchase. During the nine months ended September 30, 2020, the Partnership made several open market repurchases of the 2022 and 2025 Senior Notes that resulted in the extinguishment of $32.4 million of face value of the 2022 Senior Notes and $106.2 million of face value of the 2025 Senior Notes (the “Open Market Repurchases”). Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 and 2025 Senior Notes, plus accrued interest totaled $82.9 million and the Partnership recognized a $56.2 million gain on the extinguishment of debt during the nine months ended September 30, 2020. Debt Tender Offers . In September 2020, the Co-Issuers completed cash tender offers (the “Tender Offers”) to purchase a portion of the 2022 and 2025 Senior Notes. Upon concluding the Tender Offers, the Co-Issuers repurchased $33.5 million principal amount of the 2022 Senior Notes and $38.7 million principal amount of the 2025 Senior Notes. Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 and 2025 Senior Notes, plus accrued interest, totaled $48.7 million and the Partnership recognized a $23.3 million gain on the extinguishment of debt during the nine months ended September 30, 2020. Gain on Extinguishment of Debt. The Partnership recognized a $78.9 million gain on extinguishment of debt during the nine months ended September 30, 2020, as the result of open market repurchases of its Senior Notes. ECP Loan Repayment Open Market Repurchases Tender Offers Total During the Nine Months Ended September 30, 2020 2022 2025 Senior Notes Senior Notes Gain on repurchases of Senior Notes $ — $ 11,554 $ 46,003 $ 9,223 $ 15,479 $ 82,259 Debt issue costs (361) (143) (965) (125) (351) (1,945) Transaction cost (249) (105) (105) (465) (465) (1,389) Gain (loss) on extinguishment $ (610) $ 11,306 $ 44,933 $ 8,633 $ 14,663 $ 78,925

LIABILITY MANAGEMENT TRANSACTIO

LIABILITY MANAGEMENT TRANSACTIONS	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
LIABILITY MANAGEMENT TRANSACTIONS	7. DEBT Debt for the Partnership at September 30, 2021 and December 31, 2020, follows: September 30, 2021 December 31, 2020 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured revolving credit facility due May 13, 2022 (1) $ 725,000 $ 857,000 Permian Transmission Credit Facility : Permian Transmission's variable rate senior secured credit facility due March 8, 2028 107,000 — Less: unamortized debt issuance costs (4,936) — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 (2) 234,047 234,047 Less: unamortized debt issuance costs (497) (859) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 15, 2025 259,463 259,463 Less: unamortized debt issuance costs (1,999) (2,325) Total long-term debt $ 1,318,078 $ 1,347,326 (1) The Revolving Credit Facility was repaid in full on November 2, 2021 upon the issuance of the 2026 Secured Notes, and is therefore classified as non-current on the balance sheet. See Note 17 - Subsequent Events for additional information. (2) The indenture governing the 2022 Senior Notes was satisfied and discharged as of November 2, 2021 upon the issuance of the 2026 Secured Notes. The Co-Issuers delivered a notice of conditional redemption irrevocably calling for the redemption of all of the outstanding 2022 Senior Notes on November 12, 2021 and the Co-Issuers have irrevocably deposited with the trustee of the 2022 Senior Notes sufficient funds to redeem the 2022 Senior Notes in full on November 12, 2021. Therefore, the amounts are classified as non-current on the balance sheet. See Note 17 - Subsequent Events for additional information. Revolving Credit Facility. As of September 30, 2021, the Partnership’s wholly owned subsidiary, Summit Holdings, had a Revolving Credit Facility which allowed for revolving loans, letters of credit and swingline loans. As of September 30, 2021, the Revolving Credit Facility had $1.1 billion of commitments from lenders and was scheduled to mature on May 13, 2022. At September 30, 2021, the applicable margin for LIBOR borrowings was 3.25%, the interest rate was 3.34% and the unused portion of the Revolving Credit Facility totaled $351.1 million, subject to a commitment fee of 0.50%, after giving effect to the issuance of $23.9 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 September 30, 2021 was approximately $170.5 million. At September 30, 2021, the Revolving Credit Facility included three financial performance covenants which required 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 nine months ended September 30, 2021, the Partnership was in compliance with the Revolving Credit Facility's financial covenants, including the financial performance covenants, and there were no defaults or events of default. On November 2, 2021, a portion of the proceeds from the issuance of the 2026 Secured Notes, together with cash on hand and borrowings under the ABL Facility, was used to repay, in full, the obligations under the Revolving Credit Facility. See Note 17 - Subsequent Events for additional information. Permian Transmission Credit Facility. On March 8, 2021 (the “Permian 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 and a $15.0 million 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 unaudited condensed consolidated balance sheets. As of September 30, 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 $66.0 million, subject to a commitment fee of 0.7% after giving effect to the issuance of $2.0 million in outstanding but undrawn irrevocable standby letters of credit. As of and during the period from the Permian Closing Date to September 30, 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 Permian Closing Date to September 30, 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, unsecured 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. As of and during the nine month period ended September 30, 2021, the Partnership was in compliance with the financial covenants governing the 2022 Senior Notes. The Co-Issuers delivered a notice of conditional redemption irrevocably calling for the redemption on November 12, 2021 (the “Redemption Date”) of all of the outstanding 2022 Senior Notes at a redemption price equal to 100.0% of the principal amount of the 2022 Senior Notes to be redeemed, plus accrued and unpaid interest, if any, on the 2022 Senior Notes to be redeemed on the Redemption Date. In connection with the issuance of the 2026 Secured Notes, on November 2, 2021, the Co-Issuers irrevocably deposited with the trustee under the indenture governing the 2022 Senior Notes sufficient cash to redeem all of the 2022 Senior Notes, including the payment of all accrued and unpaid interest and all other amounts owing under the indenture governing the 2022 Senior Notes, and the indenture governing the 2022 Senior Notes was satisfied and discharged . See Note 17 - Subsequent Events for additional information. 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 unsecured 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 September 30, 2021, the Co-Issuers have the right to 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 nine month period ended September 30, 2021, the Partnership was in compliance with the financial covenants governing its 2025 Senior Notes. 8. LIABILITY MANAGEMENT TRANSACTIONS During the three and nine months ended September 30, 2020, the Partnership completed several liability management transactions, described below, that resulted in the early extinguishment of $210.8 million of the Partnership’s 2022 and 2025 Senior Notes during the nine months ended September 30, 2020. Open Market Repurchase. During the nine months ended September 30, 2020, the Partnership made several open market repurchases of the 2022 and 2025 Senior Notes that resulted in the extinguishment of $32.4 million of face value of the 2022 Senior Notes and $106.2 million of face value of the 2025 Senior Notes (the “Open Market Repurchases”). Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 and 2025 Senior Notes, plus accrued interest totaled $82.9 million and the Partnership recognized a $56.2 million gain on the extinguishment of debt during the nine months ended September 30, 2020. Debt Tender Offers . In September 2020, the Co-Issuers completed cash tender offers (the “Tender Offers”) to purchase a portion of the 2022 and 2025 Senior Notes. Upon concluding the Tender Offers, the Co-Issuers repurchased $33.5 million principal amount of the 2022 Senior Notes and $38.7 million principal amount of the 2025 Senior Notes. Total cash consideration paid to repurchase the principal amounts outstanding of the 2022 and 2025 Senior Notes, plus accrued interest, totaled $48.7 million and the Partnership recognized a $23.3 million gain on the extinguishment of debt during the nine months ended September 30, 2020. Gain on Extinguishment of Debt. The Partnership recognized a $78.9 million gain on extinguishment of debt during the nine months ended September 30, 2020, as the result of open market repurchases of its Senior Notes. ECP Loan Repayment Open Market Repurchases Tender Offers Total During the Nine Months Ended September 30, 2020 2022 2025 Senior Notes Senior Notes Gain on repurchases of Senior Notes $ — $ 11,554 $ 46,003 $ 9,223 $ 15,479 $ 82,259 Debt issue costs (361) (143) (965) (125) (351) (1,945) Transaction cost (249) (105) (105) (465) (465) (1,389) Gain (loss) on extinguishment $ (610) $ 11,306 $ 44,933 $ 8,633 $ 14,663 $ 78,925

FINANCIAL INSTRUMENTS

FINANCIAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
FINANCIAL INSTRUMENTS	9. FINANCIAL INSTRUMENTS Fair Value. A summary of the estimated fair value of our financial instruments follows. September 30, 2021 December 31, 2020 Carrying Estimated Carrying Estimated (In thousands) 2022 Senior Notes $ 233,550 $ 228,683 $ 233,188 $ 215,713 2025 Senior Notes 257,464 235,030 257,138 168,002 The balance sheet carrying values for the Revolving Credit Facility and the Permian Transmission Credit Facility represent fair value due to their floating interest rates. The fair value for the Senior Notes is based on an average of nonbinding broker quotes as of September 30, 2021 and December 31, 2020. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the Senior Notes. Interest Rate Swaps. In connection with the Permian Transmission Credit Facility, the Partnership entered into amortizing interest rate swap agreements for a notional amount of $144.0 million. These interest rate swaps manage 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 September 30, 2021, the Partnership’s interest rate swap agreements had a fair value of $1.9 million and are recorded within other current liabilities and other noncurrent liabilities within the unaudited condensed consolidated balance sheets.

PARTNERS' CAPITAL AND MEZZANINE

PARTNERS' CAPITAL AND MEZZANINE CAPITAL	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
PARTNERS' CAPITAL AND MEZZANINE CAPITAL	10. 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 September 30, 2021. Common Units Units, December 31, 2020 6,110,092 2021 Preferred Exchange Offer, net of units withheld for taxes 538,715 Common units issued for SMLP LTIP, net 106,580 ECP Warrant exercise 414,447 Units, September 30, 2021 7,169,834 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 September 30, 2021, the Partnership had 143,447 Series A Preferred Units outstanding and $26.0 million of accrued and unpaid distributions on its Series A Preferred Units. Series A Preferred Unit Exchange Offers. In April 2021, the Partnership completed an offer to exchange its Series A Preferred Units for newly issued common units, whereby it issued 538,715 SMLP common units, net of units withheld for withholding taxes, in exchange for 18,662 Series A Preferred Units. In July 2020, the Partnership completed an offer to exchange its Series A Preferred Units for newly issued common units, whereby it issued 817,845 SMLP common units, net of units withheld for withholding taxes, in exchange for 62,816 Series A Preferred Units. 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 nine months ended September 30, 2021, the Partnership elected to make PIK distributions and issued 4,558 Subsidiary Series A Preferred Units to the holders of its Subsidiary Series A Preferred Units. As of September 30, 2021, the Partnership has 89,866 Subsidiary Series A Preferred Units issued and outstanding. If the Subsidiary Series A Preferred Units were redeemed on September 30, 2021, the redemption amount would be $112.3 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 September 30, 2021: 2021 (in thousands) Balance at January 1, $ 89,658 PIK distributions 4,558 Redemption accretion 7,716 Balance at September 30, $ 101,932 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 SMP TopCo, LLC, a Delaware limited liability company and affiliate of ECP (“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 SMLP Holdings, LLC, a Delaware limited liability company and affiliate of ECP (“ECP Holdings” and together with ECP NewCo, the "ECP Entities") (the “ECP Holdings Warrant” and together with the ECP NewCo Warrant, the “ECP Warrants”). On August 5, 2021, the ECP Entities cashlessly exercised all of the ECP Warrants for an aggregate of 414,447 SMLP common units, net of the exercise price, as calculated pursuant to Section 3(c) of the ECP Warrants (the "ECP Warrant Exercise"). 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	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
EARNINGS PER UNIT	11. EARNINGS PER UNIT The following table details the components of EPU. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands, (In thousands, Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) $ 7,004 $ 25,629 $ (3,744) $ 86,112 Net income attributable to Subsidiary Series A Preferred Units (4,253) (7,298) (12,274) (9,640) Net loss attributable to noncontrolling interest — — — 3,274 Net income (loss) attributable to Summit Midstream Partners, LP 2,751 18,331 (16,018) 79,746 Less: Net income attributable to Series A Preferred Units (3,916) (6,481) (12,052) (20,731) Add: Deemed capital contribution from 2021 Preferred Exchange Offer — 54,945 8,326 54,945 Net income (loss) attributable to common limited partners (1,165) $ 66,795 (19,744) $ 113,960 Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 6,999 3,465 6,596 3,155 Effect of nonvested phantom units — 112 — 97 Weighted-average common units outstanding – diluted 6,999 3,577 6,596 3,252 Net Income (Loss) per limited partner unit: Common unit – basic $ (0.17) $ 19.28 $ (2.99) $ 36.12 Common unit – diluted $ (0.17) $ 18.67 $ (2.99) $ 35.04 Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 367 269 193 224

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	9 Months Ended
	Sep. 30, 2021
Supplemental Cash Flow Elements [Abstract]
SUPPLEMENTAL CASH FLOW INFORMATION	12. SUPPLEMENTAL CASH FLOW INFORMATION Nine Months Ended September 30, 2021 2020 (In thousands) Supplemental cash flow information: Cash interest paid $ 42,104 $ 62,441 Cash paid for taxes $ 191 $ — Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 5,614 $ 10,233 Warrant issuance for GP Buy-In Transaction $ — $ 2,300 Right-of-use assets relating to ASC Topic 842 $ — $ 2,964 Accretion of Subsidiary Series A Preferred Units $ 7,716 $ 5,856 Exercise of ECP Warrants $ 15,542 $ —

UNIT-BASED AND NONCASH COMPENSA

UNIT-BASED AND NONCASH COMPENSATION	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
UNIT-BASED AND NONCASH COMPENSATION	13. 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. Significant items to note: • For the nine-month period ended September 30, 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 period. • For the nine-month period ended September 30, 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 per common unit and vested immediately. • As of September 30, 2021, approximately 0.3 million common units remained available for future issuance under the SMLP LTIP.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	14. 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 (“2015 Blacktail Release”). As of September 30, 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 September 30, 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 their present value. A rollforward of the Partnership’s undiscounted accrued environmental remediation follows and is primarily related to the 2015 Blacktail Release. Total (In thousands) Accrued environmental remediation, December 31, 2020 $ 2,929 Payments made (1,039) Additional accruals 3,718 Accrued environmental remediation, September 30, 2021 $ 5,608 In the fourth quarter of 2020, the Partnership recognized a $17.0 million loss contingency for the 2015 Blacktail Release as a result of ongoing discussions with multiple federal and state government agencies, including the U.S. Department of Justice, the U.S. Environmental Protection Agency, the North Dakota Industrial Commission, the North Dakota Office of the Attorney General, the North Dakota Department of Environmental Quality, and the North Dakota Game and Fish Department. Subsequently, on August 4, 2021, the Partnership and several of its subsidiaries entered into the following agreements to resolve the U.S. federal and North Dakota state governments’ environmental claims with respect to the 2015 Blacktail Release: (i) a Consent Decree with (a) the U.S. Department of Justice (“DOJ”), on behalf of the U.S. Environmental Protection Agency and the U.S. Department of Interior, and (b) the State of North Dakota, on behalf of the North Dakota Department of Environmental Quality and the North Dakota Game and Fish Department (“Consent Decree”), lodged with the U.S. District Court for the District of North Dakota (“U.S. District Court”); (ii) a Plea Agreement with the United States, by and through the U.S. Attorney for the District of North Dakota, and the Environmental Crimes Section of the DOJ (“Plea Agreement”); and (iii) a Consent Agreement with the North Dakota Industrial Commission (“Consent Agreement” together with the Consent Decree and Plea Agreement, the “Global Settlement”). The Partnership increased its loss contingency for the 2015 Blacktail Release during the three months ended June 30, 2021 by $19.3 million. As of September 30, 2021, the accrued loss liability for the 2015 Blacktail Release was $36.3 million. Key terms of the Global Settlement include (i) payment of penalties and fines totaling $36.3 million, consisting of $1.25 million in natural resource damages to the federal and state governments payable after court approval of the Global Settlement, $25.0 million payable to the federal government over five years, and $10.0 million payable to the state governments over six years, with interest applied to unpaid amounts accruing at a fixed rate of 3.25%, and of which $3.1 million is expected to be paid within the next twelve months; (ii) continuation of remediation efforts at the site of the 2015 Blacktail Release; (iii) other injunctive relief including but not limited to control room management, environmental management system audit, training, and reporting; (iv) guilty pleas for one charge of negligent discharge of a harmful quantity of oil and one charge of knowing failure to immediately report a discharge of oil; and (v) organizational probation for a minimum period of three years from sentencing, including payment in full of certain components of the fines and penalty amounts. The agreements comprising the Global Settlement are subject to the approval of the U.S. District Court for the District of North Dakota (the “U.S. District Court”). The U.S. District Court entered an order making the civil components of the Global Settlement effective on September 28, 2021 and has set a hearing for December 6, 2021 on the criminal components of the Global Settlement, which if accepted by the U.S. District Court will complete approval of the Global Settlement. 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	9 Months Ended
	Sep. 30, 2021
Restructuring and Related Activities [Abstract]
RESTRUCTURING	15. RESTRUCTURING 2020 Restructuring Activities. In late 2020, management 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 three-and nine-month periods ended September 30, 2021, the Partnership expensed approximately $0.1 million and $0.9 million, respectively, 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 September 30, 2021, the Partnership has accrued and unpaid liabilities of $0.2 million associated with the 2020 Restructuring Plan activities. 2019 Restructuring Activities. In late 2019, management 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 three-and nine-month periods ended September 30, 2020, the Partnership expensed approximately $0.1 million and $3.4 million, respectively, of costs associated with these restructuring activities. These activities consisted primarily of employee-related costs and consulting costs in support of the 2019 Restructuring Plan. These costs are included within the General and administrative caption on the consolidated statement of operations. At September 30, 2021, the Partnership has accrued and unpaid liabilities of less than $0.1 million associated with the 2019 Restructuring Plan activities.

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
SEGMENT INFORMATION	16. SEGMENT INFORMATION As of September 30, 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 reports 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 nine months ended September 30, 2021, other than the investment activity described in Note 5 - Equity Method Investments, 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. September 30, 2021 December 31, 2020 (In thousands) Assets (1) : Utica Shale $ 208,715 $ 209,425 Ohio Gathering 248,373 259,888 Williston Basin 407,593 425,873 DJ Basin 193,471 199,920 Permian Basin 165,935 165,765 Piceance Basin 541,465 579,800 Barnett Shale 320,984 336,629 Marcellus Shale 171,748 176,441 Total reportable segment assets 2,258,284 2,353,741 Corporate and Other 242,393 146,076 Total assets $ 2,500,677 $ 2,499,817 (1) At September 30, 2021 and December 31, 2020, Corporate and Other included $233.6 million and $132.9 million respectively, relating to our investment in Double E (included in the Investment in equity method investees caption of the unaudited condensed consolidated balance sheet). Segment adjusted EBITDA by reportable segment follows. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 8,328 $ 7,453 $ 26,700 $ 24,074 Ohio Gathering 6,690 7,129 20,403 22,582 Williston Basin 11,276 11,713 31,707 40,632 DJ Basin 7,446 4,766 17,899 15,016 Permian Basin 559 893 1,729 4,302 Piceance Basin 18,908 21,503 60,266 66,794 Barnett Shale 9,637 7,205 26,542 24,475 Marcellus Shale 5,702 6,022 17,171 16,230 Total of reportable segments' measures of profit $ 68,546 $ 66,684 $ 202,417 $ 214,105 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Reconciliation of income (loss) before income taxes and income from equity method investees to total of reportable segments' measures of profit: Income (loss) before income taxes and income from equity method investees $ 4,850 $ 25,132 $ (10,779) $ 78,862 Add: Corporate and Other expense 10,895 6,874 58,953 28,484 Interest expense 15,530 19,018 44,985 64,836 Gain on early extinguishment of debt — (24,690) — (78,925) Depreciation and amortization (1) 31,226 29,739 88,570 89,505 Proportional adjusted EBITDA for equity method investees 6,690 7,129 20,403 22,582 Adjustments related to MVC shortfall payments — 2,292 — (859) Adjustments related to capital reimbursement activity (1,549) (328) (5,019) (776) Unit-based and noncash compensation 868 1,622 3,883 6,191 Gain on asset sales, net (212) (104) (352) (270) Long-lived asset impairment 248 — 1,773 4,475 Total of reportable segments' measures of profit $ 68,546 $ 66,684 $ 202,417 $ 214,105 (1) Includes the amortization expense associated with our favorable gas gathering contracts as reported in other revenues.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	17. SUBSEQUENT EVENTS 2026 Secured Notes and Redemption of 2022 Senior Notes On November 2, 2021, the Co-Issuers issued $700.0 million of 8.500% Senior Secured Second Lien Notes due 2026 (the “2026 Secured Notes”) to eligible purchasers pursuant to Rule 144A and Regulation S of the Securities Act, at a price of 98.5% of their face value. The 2026 Secured Notes will pay interest semi-annually on April 15 and October 15 of each year, commencing on April 15, 2022, and will be jointly and severally guaranteed, on a senior second-priority secured basis (subject to permitted liens), by the Partnership and each restricted subsidiary of the Partnership (other than the Co-Issuers) that is an obligor under the ABL Agreement (as defined below), or under the Co-Issuers’ 2025 Senior Notes on the issue date of the 2026 Secured Notes. The 2026 Secured Notes will mature on October 15, 2026; provided that, if the outstanding amount of the 2025 Senior Notes (or any refinancing indebtedness in respect thereof that has a final maturity on or prior to the date that is 91 days after the Initial Maturity Date (as defined in the 2026 Secured Notes Indenture)) is greater than or equal to $50.0 million on January 14, 2025, which is 91 days prior to the scheduled maturity date of the 2025 Senior Notes, then the 2026 Secured Notes will mature on January 14, 2025. The Partnership used the net proceeds from the offering of the 2026 Secured Notes, together with cash on hand and borrowings under the ABL Facility (as defined below), to repay in full all of Summit Holdings’ obligations under the Revolving Credit Facility. Additionally, as previously announced, the Co-Issuers delivered a notice of conditional redemption calling for the redemption irrevocably calling for the redemption of all of the outstanding 2022 Senior Notes at a redemption price equal to 100.0% of the principal amount of the 2022 Senior Notes, plus accrued and unpaid interest, if any, on the 2022 Senior Notes to be redeemed on the Redemption Date. In connection with the issuance of the 2026 Secured Notes, on November 2, 2021, the Co-Issuers irrevocably deposited with the trustee under the indenture governing the 2022 Senior Notes sufficient cash to redeem all of the 2022 Senior Notes, including the payment of all accrued and unpaid interest and all other amounts owing under the indenture governing the 2022 Senior Notes, and the indenture governing the 2022 Senior Notes was satisfied and discharged . 2026 Secured Notes Indenture The Co-Issuers issued the 2026 Secured Notes pursuant to an indenture (the “2026 Secured Notes Indenture”), dated as of November 2, 2021, by and among the Co-Issuers, the Partnership, any other Restricted Subsidiary (as defined in the 2026 Secured Notes Indenture) of the Partnership that provides a Notes Guarantee (as defined in the 2026 Secured Notes Indenture) and Regions Bank, as trustee (the “Trustee”) and collateral agent, setting forth specific terms applicable to the 2026 Secured Notes. At any time prior to October 15, 2023, the Co-Issuers may on any one or more occasions redeem up to 35% of the aggregate principal amount of the 2026 Secured Notes (including any additional notes) issued under the 2026 Secured Notes Indenture at a redemption price of 108.5% of the principal amount of the 2026 Secured Notes, plus accrued and unpaid interest, if any, to, but not including, the redemption date, in an amount not greater than the net cash proceeds of certain equity offerings by the Partnership, provided that: (i) at least 65% of the initial aggregate principal amount of the 2026 Secured Notes (including any additional notes) remains outstanding immediately after the occurrence of such redemption (excluding notes held by the Partnership and its subsidiaries); and (ii) the redemption occurs within 180 days of the date of the closing of each such equity offering by the Partnership. On and after October 15, 2023, the Co-Issuers may redeem all or part of the 2026 Secured Notes at redemption prices (expressed as percentages of principal amount) equal to: (a) 104.250% for the twelve-month period beginning October 15, 2023; (b) 102.125% for the twelve-month period beginning October 15, 2024; and (c) 100.000% for the twelve-month period beginning on October 15, 2025 and at any time thereafter, in each case plus accrued and unpaid interest, if any, to, but not including, the redemption date. In certain circumstances, the Co-Issuers will be required to offer to purchase the 2026 Secured Notes with excess proceeds from asset sales, excess cash flow and upon the occurrence of certain change of control events. The 2026 Secured Notes Indenture restricts the Partnership’s and its Restricted Subsidiaries’ ability and the ability of certain of their subsidiaries to: (i) incur additional debt or issue preferred stock; (ii) make distributions, repurchase equity or redeem junior lien, unsecured or subordinated debt; (iii) make payments on junior lien, unsecured or subordinated indebtedness; (iv) create liens or other encumbrances; (v) make investments, loans or other guarantees; (vi) engage in transactions with affiliates; and (viii) make acquisitions or merge or consolidate with another entity. These covenants are subject both to a number of important exceptions and qualifications. At any time when the 2026 Secured Notes are rated investment grade by at least two of Moody’s Investors Service, Inc., Standard & Poor’s Ratings Services or Fitch Ratings, Inc., no default under the 2026 Secured Notes Indenture has occurred and is continuing, many of these covenants will terminate. The 2026 Secured Notes Indenture contains certain events of default customary for instruments of this type. In the case of an event of default arising from certain events of bankruptcy, insolvency or reorganization with respect to either Co-Issuer, the Partnership, and certain significant subsidiaries of the Partnership, all outstanding Notes will become due and payable immediately without further action or notice. If any other event of default occurs and is continuing, the Trustee or the holders of at least 25% in principal amount of the then outstanding Notes may declare all the 2026 Secured Notes to be due and payable immediately. Collateral Agreement On November 2, 2021, the Co-Issuers, as pledgors and grantors, entered into, in connection with the 2026 Secured Notes Indenture, a Collateral Agreement (Second Lien), with the Partnership, as a pledgor, each subsidiary guarantor listed therein and Regions Bank, as collateral agent (the “Collateral Agreement”). Pursuant to the Collateral Agreement and the 2026 Secured Notes Indenture, the obligations under the 2026 Secured Notes Indenture are (or, subject to post-closing periods for certain types of collateral, will be) generally secured by a second priority lien on and security interest in (subject to permitted liens) the assets of the Partnership, the Co-Issuers and the subsidiary guarantors securing their obligations under the ABL Facility (as described below under “—ABL Facility”). ABL Facility Concurrently with the issuance of the 2026 Secured Notes, on November 2, 2021, Summit Holdings, as borrower, entered into a first-lien, senior secured credit agreement, with the Partnership, the subsidiaries party thereto, Bank of America, N.A., as agent, and the several lenders and other agents party thereto, consisting of a $400.0 million asset-based revolving credit facility (the “ABL Facility”), subject to a borrowing base comprised of a percentage of eligible accounts receivable of Summit Holdings and its subsidiaries that guarantee the ABL Facility (collectively, the “ABL Facility Subsidiary Guarantors”) and a percentage of eligible above-ground fixed assets including eligible compression units, processing plants, compression stations and related equipment of Summit Holdings and the ABL Facility Subsidiary Guarantors. Summit Holdings entered into the ABL Facility pursuant to that certain Loan and Security Agreement (the “ABL Agreement”), dated as of November 2, 2021, by and among Summit Holdings, as borrower, the Partnership, the ABL Facility Subsidiary Guarantors, Bank of America, N.A., as agent, ING Capital LLC, Royal Bank of Canada and Regions Bank, as co-syndication agents, and Bank of America, N.A., ING Capital LLC, RBC Capital Markets and Regions Capital Markets, as joint lead arrangers and joint bookrunners. The ABL Facility will mature on May 1, 2026; provided that, (a) if the outstanding amount of the 2025 Senior Notes (or any permitted refinancing indebtedness in respect thereof that has a final maturity, scheduled amortization or any other scheduled repayment, mandatory prepayment, mandatory redemption or sinking fund obligation prior to the date that is 120 days after the Termination Date (as defined in the ABL Agreement)) on such date equals or exceeds $50,000,000, then the ABL Facility will mature on December 13, 2024 and (b) if both (i) any amount of the 2025 Senior Notes (or any permitted refinancing indebtedness in respect thereof that has a final maturity, scheduled amortization or any other scheduled repayment, mandatory prepayment, mandatory redemption or sinking fund obligation prior to the date that is 120 days after the Termination Date) is outstanding on such date and (ii) Liquidity (as defined in the ABL Agreement) is less than an amount equal to the sum of the then aggregate outstanding principal amount of the 2025 Senior Notes (or any permitted refinancing indebtedness in respect thereof that has a final maturity, scheduled amortization or any other scheduled repayment, mandatory prepayment, mandatory redemption or sinking fund obligation prior to the date that is 120 days after the Termination Date) plus the Threshold Amount (as defined in the ABL Agreement) on such date, then the ABL Facility will mature on January 14, 2025. The ABL Facility (together with certain Secured Bank Product Obligations (as defined in the ABL Agreement)) will be jointly and severally guaranteed, on a senior first-priority secured basis (subject to permitted liens), by the Partnership, Summit Holdings and each of the ABL Facility Subsidiary Guarantors. The ABL Facility restricts, among other things, Summit Holdings’ and its Restricted Subsidiaries’ (as defined in the ABL Agreement) ability and the ability of certain of their subsidiaries to: (i) incur additional debt or issue preferred stock; (ii) make distributions or repurchase equity; (iii) make payments on or redeem junior lien, unsecured or subordinated indebtedness; (iv) create liens or other encumbrances; (v) make investments, loans or other guarantees; (vi) engage in transactions with affiliates; and (viii) make acquisitions or merge or consolidate with another entity. These covenants are subject both to a number of important exceptions and qualifications. The ABL Facility requires that Summit Holdings not permit (i) the First Lien Net Leverage Ratio (as defined in the ABL Agreement) as of the last day of any fiscal quarter to be greater than 2.50:1.00, or (ii) the Interest Coverage Ratio (as defined in the ABL Agreement) as of the last day of any fiscal quarter to be less than 2.00:1.00. The ABL Facility contains certain events of default customary for instruments of this type. In the case of an event of default arising from certain events of bankruptcy, insolvency or reorganization with respect to Summit Holdings, all outstanding Obligations (as defined in the ABL Agreement) will become due and payable immediately without further action or notice and all commitments under the ABL Facility will terminate. Pursuant to the ABL Agreement, the Obligations (as defined in the ABL Agreement) are (or, subject to post-closing periods for certain types of collateral, will be) generally secured by a first priority lien on and security interest in (subject to permitted liens), subject to certain exclusions and limitations set forth in the ABL Agreement, (i) substantially all of the personal property of Summit Holdings and the ABL Facility Subsidiary Guarantors, (ii) all equity interests in Summit Holdings and certain other entities, all debt securities and certain rights related to the foregoing, in each case, owned by the Partnership, (iii) Closing Date Material Gathering Station Real Property and Closing Date Pipeline Material Gathering Station Real Property (each, as defined in the ABL Agreement) and certain other material real property interests (including improvements thereon) of Summit Holdings and the ABL Facility Subsidiary Guarantors as provided in the ABL Agreement and (iv) all proceeds of the foregoing collateral. Intercreditor Agreement On November 2, 2021, in connection with the entry into the ABL Facility and issuance of the 2026 Secured Notes, Summit Holdings and the other guarantors party thereto entered into an Intercreditor Agreement (the “Intercreditor Agreement”) with Bank of America, N.A., as first lien representative and collateral agent for the initial first lien claimholders, Regions Bank, as second lien representative for the initial second lien claimholders and collateral agent for the initial second lien claimholders, establishing (i) a first-priority lien (subject to permitted liens) status for the liens on the collateral securing the ABL Facility and any additional first-lien indebtedness and (ii) a junior priority lien (subject to permitted liens) status for the liens on the collateral securing the 2026 Secured Notes and any additional second-lien indebtedness.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	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.
Use of Estimates	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.
Consolidation	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	The Partnership considers 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.
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	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. 2020-6 Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815 – 40) (“ASU 2020-6”). ASU 2020-6 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 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 2020-6 to determine its impact on the Partnership’s consolidated financial statements and disclosures. ASU No. 2020-4 Reference Rate Reform (“ASU 2020-4”). ASU 2020-4 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 2020-4 are effective as of March 12, 2020 through December 31, 2022. The Partnership is currently evaluating the provisions of ASU 2020-4 to determine its impact on the Partnership’s consolidated financial statements and disclosures.

REVENUE (Tables)

REVENUE (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments	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 $ 21,192 $ 80,064 $ 62,179 $ 51,645 $ 35,200 $ 21,071
Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments	Revenue by Category. In the following tables, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 16 – Segment Information. Three Months Ended September 30, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 9,170 $ — $ — $ 9,170 Williston Basin 12,894 12,692 4,620 30,206 DJ Basin 6,180 153 644 6,977 Permian Basin 1,879 7,925 117 9,921 Piceance Basin 24,104 1,166 1,114 26,384 Barnett Shale 10,162 185 1,577 11,924 Marcellus Shale 6,535 — — 6,535 Total reportable segments 70,924 22,121 8,072 101,117 Corporate and Other — — 928 928 Total $ 70,924 $ 22,121 $ 9,000 $ 102,045 Nine Months Ended September 30, 2021 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 29,090 $ — $ — $ 29,090 Williston Basin 38,043 33,120 13,369 84,532 DJ Basin 18,334 568 3,204 22,106 Permian Basin 6,340 21,318 354 28,012 Piceance Basin 74,415 4,044 3,523 81,982 Barnett Shale 29,934 251 3,649 33,834 Marcellus Shale 19,348 — — 19,348 Total reportable segments 215,504 59,301 24,099 298,904 Corporate and Other — — 2,500 2,500 Total $ 215,504 $ 59,301 $ 26,599 $ 301,404 Three Months Ended September 30, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,385 $ — $ — $ 8,385 Williston Basin 10,941 4,958 3,136 19,035 DJ Basin 6,051 17 826 6,894 Permian Basin 2,595 4,803 168 7,566 Piceance Basin 26,576 528 1,233 28,337 Barnett Shale 10,545 477 1,399 12,421 Marcellus Shale 6,871 — — 6,871 Total reportable segments 71,964 10,783 6,762 89,509 Corporate and Other — — 644 644 Total $ 71,964 $ 10,783 $ 7,406 $ 90,153 Nine Months Ended September 30, 2020 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 26,885 $ — $ — $ 26,885 Williston Basin 47,145 12,413 9,054 68,612 DJ Basin 18,134 158 2,853 21,145 Permian Basin 7,617 13,537 481 21,635 Piceance Basin 79,987 1,932 3,394 85,313 Barnett Shale 30,865 7,206 4,437 42,508 Marcellus Shale 19,034 — — 19,034 Total reportable segments 229,667 35,246 20,219 285,132 Corporate and Other — — 1,931 1,931 Total $ 229,667 $ 35,246 $ 22,150 $ 287,063
Schedule of Information about Contract Assets from Contracts with Customers	The following table provides information about contract assets from contracts with customers: Total (In thousands) Contract assets, December 31, 2020 $ 2,026 Additions 7,130 Transfers out (973) Contract assets, September 30, 2021 $ 8,183

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Details of the Partnership’s property, plant and equipment follows. September 30, 2021 December 31, 2020 (In thousands) Gathering and processing systems and related equipment $ 2,220,218 $ 2,213,501 Construction in progress 49,781 60,443 Land and line fill 10,440 10,440 Other 59,287 61,340 Total 2,339,726 2,345,724 Less: accumulated depreciation (591,552) (528,178) Property, plant and equipment, net $ 1,748,174 $ 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Depreciation expense $ 23,867 $ 21,537 $ 66,651 $ 64,899 Capitalized interest 85 1,449 395 2,268

EQUITY METHOD INVESTMENTS (Tabl

EQUITY METHOD INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Details of the Partnership’s equity method investments follows. September 30, 2021 December 31, 2020 (In thousands) Double E $ 233,612 $ 132,852 Ohio Gathering 248,373 259,888 Total $ 481,985 $ 392,740 2021 (In thousands) Investment in Ohio Gathering, September 30, $ 248,373 September cash distributions 2,163 Basis difference 210,093 Investment in Ohio Gathering (Books and records), August 31, $ 460,629

DEFERRED REVENUE (Tables)

DEFERRED REVENUE (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Contract with Customer, Contract Asset, Contract Liability, and Receivable	Total (In thousands) Current deferred revenue, January 1, 2021 $ 9,988 Add: additions 5,606 Less: revenue recognized (5,018) Current deferred revenue, September 30, 2021 $ 10,576 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2021 $ 48,250 Add: additions 632 Less: reclassification to current deferred revenue (5,634) Noncurrent deferred revenue, September 30, 2021 $ 43,248

DEBT (Tables)

DEBT (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Debt	Debt for the Partnership at September 30, 2021 and December 31, 2020, follows: September 30, 2021 December 31, 2020 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured revolving credit facility due May 13, 2022 (1) $ 725,000 $ 857,000 Permian Transmission Credit Facility : Permian Transmission's variable rate senior secured credit facility due March 8, 2028 107,000 — Less: unamortized debt issuance costs (4,936) — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 (2) 234,047 234,047 Less: unamortized debt issuance costs (497) (859) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 15, 2025 259,463 259,463 Less: unamortized debt issuance costs (1,999) (2,325) Total long-term debt $ 1,318,078 $ 1,347,326 (1) The Revolving Credit Facility was repaid in full on November 2, 2021 upon the issuance of the 2026 Secured Notes, and is therefore classified as non-current on the balance sheet. See Note 17 - Subsequent Events for additional information.

LIABILITY MANAGEMENT TRANSACT_2

LIABILITY MANAGEMENT TRANSACTIONS (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Extinguishment of Debt	ECP Loan Repayment Open Market Repurchases Tender Offers Total During the Nine Months Ended September 30, 2020 2022 2025 Senior Notes Senior Notes Gain on repurchases of Senior Notes $ — $ 11,554 $ 46,003 $ 9,223 $ 15,479 $ 82,259 Debt issue costs (361) (143) (965) (125) (351) (1,945) Transaction cost (249) (105) (105) (465) (465) (1,389) Gain (loss) on extinguishment $ (610) $ 11,306 $ 44,933 $ 8,633 $ 14,663 $ 78,925

FINANCIAL INSTRUMENTS (Tables)

FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments	A summary of the estimated fair value of our financial instruments follows. September 30, 2021 December 31, 2020 Carrying Estimated Carrying Estimated (In thousands) 2022 Senior Notes $ 233,550 $ 228,683 $ 233,188 $ 215,713 2025 Senior Notes 257,464 235,030 257,138 168,002

PARTNERS' CAPITAL AND MEZZANI_2

PARTNERS' CAPITAL AND MEZZANINE CAPITAL (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2021. Common Units Units, December 31, 2020 6,110,092 2021 Preferred Exchange Offer, net of units withheld for taxes 538,715 Common units issued for SMLP LTIP, net 106,580 ECP Warrant exercise 414,447 Units, September 30, 2021 7,169,834
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net	The following table shows the change in our Subsidiary Series A Preferred Unit balance from January 1, 2021 to September 30, 2021: 2021 (in thousands) Balance at January 1, $ 89,658 PIK distributions 4,558 Redemption accretion 7,716 Balance at September 30, $ 101,932

EARNINGS PER UNIT (Tables)

EARNINGS PER UNIT (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table details the components of EPU. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands, (In thousands, Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) $ 7,004 $ 25,629 $ (3,744) $ 86,112 Net income attributable to Subsidiary Series A Preferred Units (4,253) (7,298) (12,274) (9,640) Net loss attributable to noncontrolling interest — — — 3,274 Net income (loss) attributable to Summit Midstream Partners, LP 2,751 18,331 (16,018) 79,746 Less: Net income attributable to Series A Preferred Units (3,916) (6,481) (12,052) (20,731) Add: Deemed capital contribution from 2021 Preferred Exchange Offer — 54,945 8,326 54,945 Net income (loss) attributable to common limited partners (1,165) $ 66,795 (19,744) $ 113,960 Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 6,999 3,465 6,596 3,155 Effect of nonvested phantom units — 112 — 97 Weighted-average common units outstanding – diluted 6,999 3,577 6,596 3,252 Net Income (Loss) per limited partner unit: Common unit – basic $ (0.17) $ 19.28 $ (2.99) $ 36.12 Common unit – diluted $ (0.17) $ 18.67 $ (2.99) $ 35.04 Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 367 269 193 224

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2021
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Nine Months Ended September 30, 2021 2020 (In thousands) Supplemental cash flow information: Cash interest paid $ 42,104 $ 62,441 Cash paid for taxes $ 191 $ — Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 5,614 $ 10,233 Warrant issuance for GP Buy-In Transaction $ — $ 2,300 Right-of-use assets relating to ASC Topic 842 $ — $ 2,964 Accretion of Subsidiary Series A Preferred Units $ 7,716 $ 5,856 Exercise of ECP Warrants $ 15,542 $ —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 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 2015 Blacktail Release. Total (In thousands) Accrued environmental remediation, December 31, 2020 $ 2,929 Payments made (1,039) Additional accruals 3,718 Accrued environmental remediation, September 30, 2021 $ 5,608

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Reconciliation of Assets from Segment to Consolidated	Assets by reportable segment follow. September 30, 2021 December 31, 2020 (In thousands) Assets (1) : Utica Shale $ 208,715 $ 209,425 Ohio Gathering 248,373 259,888 Williston Basin 407,593 425,873 DJ Basin 193,471 199,920 Permian Basin 165,935 165,765 Piceance Basin 541,465 579,800 Barnett Shale 320,984 336,629 Marcellus Shale 171,748 176,441 Total reportable segment assets 2,258,284 2,353,741 Corporate and Other 242,393 146,076 Total assets $ 2,500,677 $ 2,499,817 (1) At September 30, 2021 and December 31, 2020, Corporate and Other included $233.6 million and $132.9 million respectively, relating to our investment in Double E (included in the Investment in equity method investees caption of the unaudited condensed consolidated balance sheet).
Reconciliation of Revenue from Segments to Consolidated	Segment adjusted EBITDA by reportable segment follows. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 8,328 $ 7,453 $ 26,700 $ 24,074 Ohio Gathering 6,690 7,129 20,403 22,582 Williston Basin 11,276 11,713 31,707 40,632 DJ Basin 7,446 4,766 17,899 15,016 Permian Basin 559 893 1,729 4,302 Piceance Basin 18,908 21,503 60,266 66,794 Barnett Shale 9,637 7,205 26,542 24,475 Marcellus Shale 5,702 6,022 17,171 16,230 Total of reportable segments' measures of profit $ 68,546 $ 66,684 $ 202,417 $ 214,105
Reconciliation Of Net Income To Adjusted EBITDA	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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Reconciliation of income (loss) before income taxes and income from equity method investees to total of reportable segments' measures of profit: Income (loss) before income taxes and income from equity method investees $ 4,850 $ 25,132 $ (10,779) $ 78,862 Add: Corporate and Other expense 10,895 6,874 58,953 28,484 Interest expense 15,530 19,018 44,985 64,836 Gain on early extinguishment of debt — (24,690) — (78,925) Depreciation and amortization (1) 31,226 29,739 88,570 89,505 Proportional adjusted EBITDA for equity method investees 6,690 7,129 20,403 22,582 Adjustments related to MVC shortfall payments — 2,292 — (859) Adjustments related to capital reimbursement activity (1,549) (328) (5,019) (776) Unit-based and noncash compensation 868 1,622 3,883 6,191 Gain on asset sales, net (212) (104) (352) (270) Long-lived asset impairment 248 — 1,773 4,475 Total of reportable segments' measures of profit $ 68,546 $ 66,684 $ 202,417 $ 214,105 (1) Includes the amortization expense associated with our favorable gas gathering contracts as reported in other revenues.

ORGANIZATION, BUSINESS OPERAT_2

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION (Details)	May 28, 2020USD ($)shares	May 27, 2020shares	Nov. 02, 2021USD ($)	Sep. 30, 2021shares	Dec. 31, 2020shares	Nov. 17, 2020USD ($)shares	Nov. 09, 2020shares	Nov. 08, 2020shares
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)				7,169,834	6,110,092
Subsequent Event | 2026 Notes
Organization And Business Operations [Line Items]
Debt offering | $			$ 700,000,000
Stated interest rate (as a percent)			8.50%
Subsequent Event | ABL Revolver
Organization And Business Operations [Line Items]
Borrowing capacity | $			$ 400,000,000
Common Units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common units not pledged as collateral (in shares)								5,700,000
Common limited partner capital (in 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 (in shares)	2,300,000					2,300,000
Common units not pledged as collateral (in shares)	700,000					34,600,000	34,600,000
Stock split, conversion ratio	0.0667
Common units issued prior to reverse unit split (in shares)		10,700,000
Treasury stock (in shares)		16,600,000		1,100,000
Summit Investments
Organization And Business Operations [Line Items]
Cash paid to acquire investment | $	$ 35,000,000
Summit Investments | Common Units
Organization And Business Operations [Line Items]
Common units issued prior to reverse unit split (in shares)		10,000,000
Number of common units purchased (in shares)	700,000
SMP Holdings
Organization And Business Operations [Line Items]
Debt discharge and restructuring | $						$ 155,200,000

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Restricted cash	$ 756	$ 0

REVENUE REVENUE - Schedule of E

REVENUE REVENUE - Schedule of Estimated Revenue Expected to be Recognized (Details) - Gathering services and related fees $ in Thousands	Sep. 30, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 21,192
Revenue, remaining performance obligation, expected timing of satisfaction	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 80,064
Revenue, remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 62,179
Revenue, remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 51,645
Revenue, remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 35,200
Revenue, remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 21,071
Revenue, remaining performance obligation, expected timing of satisfaction

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 102,045	$ 90,153	$ 301,404	$ 287,063
Reportable Segments
Disaggregation of Revenue [Line Items]
Total revenues	101,117	89,509	298,904	285,132
Reportable Segments | Utica Shale
Disaggregation of Revenue [Line Items]
Total revenues	9,170	8,385	29,090	26,885
Reportable Segments | Williston Basin
Disaggregation of Revenue [Line Items]
Total revenues	30,206	19,035	84,532	68,612
Reportable Segments | DJ Basin
Disaggregation of Revenue [Line Items]
Total revenues	6,977	6,894	22,106	21,145
Reportable Segments | Permian Basin
Disaggregation of Revenue [Line Items]
Total revenues	9,921	7,566	28,012	21,635
Reportable Segments | Piceance Basin
Disaggregation of Revenue [Line Items]
Total revenues	26,384	28,337	81,982	85,313
Reportable Segments | Barnett Shale
Disaggregation of Revenue [Line Items]
Total revenues	11,924	12,421	33,834	42,508
Reportable Segments | Marcellus Shale
Disaggregation of Revenue [Line Items]
Total revenues	6,535	6,871	19,348	19,034
Segment Reconciling Items
Disaggregation of Revenue [Line Items]
Total revenues	928	644	2,500	1,931
Gathering services and related fees
Disaggregation of Revenue [Line Items]
Total revenues	70,924	71,964	215,504	229,667
Gathering services and related fees | Reportable Segments
Disaggregation of Revenue [Line Items]
Total revenues	70,924	71,964	215,504	229,667
Gathering services and related fees | Reportable Segments | Utica Shale
Disaggregation of Revenue [Line Items]
Total revenues	9,170	8,385	29,090	26,885
Gathering services and related fees | Reportable Segments | Williston Basin
Disaggregation of Revenue [Line Items]
Total revenues	12,894	10,941	38,043	47,145
Gathering services and related fees | Reportable Segments | DJ Basin
Disaggregation of Revenue [Line Items]
Total revenues	6,180	6,051	18,334	18,134
Gathering services and related fees | Reportable Segments | Permian Basin
Disaggregation of Revenue [Line Items]
Total revenues	1,879	2,595	6,340	7,617
Gathering services and related fees | Reportable Segments | Piceance Basin
Disaggregation of Revenue [Line Items]
Total revenues	24,104	26,576	74,415	79,987
Gathering services and related fees | Reportable Segments | Barnett Shale
Disaggregation of Revenue [Line Items]
Total revenues	10,162	10,545	29,934	30,865
Gathering services and related fees | Reportable Segments | Marcellus Shale
Disaggregation of Revenue [Line Items]
Total revenues	6,535	6,871	19,348	19,034
Gathering services and related fees | Segment Reconciling Items
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Natural gas, NGLs and condensate sales
Disaggregation of Revenue [Line Items]
Total revenues	22,121	10,783	59,301	35,246
Natural gas, NGLs and condensate sales | Reportable Segments
Disaggregation of Revenue [Line Items]
Total revenues	22,121	10,783	59,301	35,246
Natural gas, NGLs and condensate sales | Reportable Segments | Utica Shale
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Natural gas, NGLs and condensate sales | Reportable Segments | Williston Basin
Disaggregation of Revenue [Line Items]
Total revenues	12,692	4,958	33,120	12,413
Natural gas, NGLs and condensate sales | Reportable Segments | DJ Basin
Disaggregation of Revenue [Line Items]
Total revenues	153	17	568	158
Natural gas, NGLs and condensate sales | Reportable Segments | Permian Basin
Disaggregation of Revenue [Line Items]
Total revenues	7,925	4,803	21,318	13,537
Natural gas, NGLs and condensate sales | Reportable Segments | Piceance Basin
Disaggregation of Revenue [Line Items]
Total revenues	1,166	528	4,044	1,932
Natural gas, NGLs and condensate sales | Reportable Segments | Barnett Shale
Disaggregation of Revenue [Line Items]
Total revenues	185	477	251	7,206
Natural gas, NGLs and condensate sales | Reportable Segments | Marcellus Shale
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Natural gas, NGLs and condensate sales | Segment Reconciling Items
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	9,000	7,406	26,599	22,150
Other revenues | Reportable Segments
Disaggregation of Revenue [Line Items]
Total revenues	8,072	6,762	24,099	20,219
Other revenues | Reportable Segments | Utica Shale
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other revenues | Reportable Segments | Williston Basin
Disaggregation of Revenue [Line Items]
Total revenues	4,620	3,136	13,369	9,054
Other revenues | Reportable Segments | DJ Basin
Disaggregation of Revenue [Line Items]
Total revenues	644	826	3,204	2,853
Other revenues | Reportable Segments | Permian Basin
Disaggregation of Revenue [Line Items]
Total revenues	117	168	354	481
Other revenues | Reportable Segments | Piceance Basin
Disaggregation of Revenue [Line Items]
Total revenues	1,114	1,233	3,523	3,394
Other revenues | Reportable Segments | Barnett Shale
Disaggregation of Revenue [Line Items]
Total revenues	1,577	1,399	3,649	4,437
Other revenues | Reportable Segments | Marcellus Shale
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Other revenues | Segment Reconciling Items
Disaggregation of Revenue [Line Items]
Total revenues	$ 928	$ 644	$ 2,500	$ 1,931

REVENUE - Schedule of Informati

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Contract With Customer, Contract Asset, Contract Liability, and Receivable [Roll Forward]
Contract assets, beginning of period	$ 2,026
Additions	7,130
Transfers out	(973)
Contract assets, end of period	$ 8,183

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue From Contract With Customer [Line Items]
Receivables with customers	$ 56,100		$ 56,100		$ 57,500
Contract assets included in accounts receivable	8,183		8,183		$ 2,026
Gathering services and related fees
Revenue From Contract With Customer [Line Items]
Contract with customer, liability, revenue recognized	$ 2,300	$ 2,400	$ 5,600	$ 7,100

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total	$ 2,339,726	$ 2,345,724
Less: accumulated depreciation	(591,552)	(528,178)
Property, plant and equipment, net	1,748,174	1,817,546
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Total	2,220,218	2,213,501
Construction in progress
Property, Plant and Equipment [Line Items]
Total	49,781	60,443
Land and line fill
Property, Plant and Equipment [Line Items]
Total	10,440	10,440
Other
Property, Plant and Equipment [Line Items]
Total	$ 59,287	$ 61,340

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 23,867	$ 21,537	$ 66,651	$ 64,899
Capitalized interest	$ 85	$ 1,449	$ 395	$ 2,268

EQUITY METHOD INVESTMENTS - Sch

EQUITY METHOD INVESTMENTS - Schedule of Equity Method Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment in equity method investees	$ 481,985		$ 392,740
Double E
Schedule of Equity Method Investments [Line Items]
Investment in equity method investees	233,612		132,852
OGC
Schedule of Equity Method Investments [Line Items]
Investment in equity method investees	$ 248,373	$ 460,629	$ 259,888

EQUITY METHOD INVESTMENTS - Nar

EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment in equity method investment	$ 102,109	$ 92,072
Double E
Schedule of Equity Method Investments [Line Items]
Investment in equity method investment	102,100	92,100
Interest cost capitalized	$ 2,500	$ 1,400
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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) In Equity Method Investments [Roll Forward]
Ending balance	$ 481,985	$ 481,985
September cash distributions		20,004	$ 19,859
Beginning balance		392,740
OGC
Increase (Decrease) In Equity Method Investments [Roll Forward]
Ending balance	248,373	248,373
September cash distributions	2,163
Basis difference	$ 210,093
Beginning balance		$ 259,888

DEFERRED REVENUE - Rollforward

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Change in Contract with Customer, Liability, Current [Roll Forward]
Current deferred revenue, beginning balance	$ 9,988
Add: additions	5,606
Less: revenue recognized	(5,018)
Current deferred revenue, ending balance	10,576
Change in Contract with Customer, Liability, Noncurrent [Roll Forward]
Noncurrent deferred revenue, beginning balance	48,250
Add: additions	632
Less: reclassification to current deferred revenue	(5,634)
Noncurrent deferred revenue, ending balance	$ 43,248

DEBT - Components of Long-Term

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Long-term debt	$ 1,318,078	$ 1,347,326
Revolving Credit Facility: Summit Holdings' variable rate senior secured revolving credit facility due May 13, 2022 (1)
Line of Credit Facility [Line Items]
Revolving credit facility	725,000	857,000
Permian Transmission Credit Facility: Permian Transmission's variable rate senior secured credit facility due March 8, 2028
Line of Credit Facility [Line Items]
Secured notes	107,000	0
Less unamortized debt issuance costs	(4,936)	0
2022 Senior Notes: Summit Holdings' 5.5% senior unsecured notes due August 15, 2022 (2)
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	(497)	(859)
Unsecured notes	234,047	$ 234,047
Stated interest rate (as a percent)		5.50%
2025 Senior Notes: Summit Holdings' 5.75% senior unsecured notes due April 15, 2025
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	(1,999)	$ (2,325)
Unsecured notes	$ 259,463	$ 259,463
Stated interest rate (as a percent)		5.75%

DEBT - Revolving Credit Facilit

DEBT - Revolving Credit Facility (Narrative) (Details) - Revolving credit facility	9 Months Ended
	Sep. 30, 2021USD ($)
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,100,000,000
Interest rate at period end	3.34%
Unused portion under the facility	$ 351,100,000
Commitment fee on unused portion of the facility (as a percent)	0.50%
Secured notes	$ 23,900,000
Borrowing capacity	$ 170,500,000
Minimum
Line of Credit Facility [Line Items]
Ratio of consolidated trailing 12-month EBITDA to net interest expense	2.50
Maximum
Line of Credit Facility [Line Items]
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
LIBOR
Line of Credit Facility [Line Items]
Applicable margin (as a percent)	3.25%

DEBT - Permian Transmission Cre

DEBT - Permian Transmission Credit Facility (Narrative) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Mar. 08, 2021
Line of Credit Facility [Line Items]
Debt default amount	$ 0
Credit Agreement
Line of Credit Facility [Line Items]
Borrowing capacity		$ 175,000,000
Interest rate during period (as a percent)	2.50%
Unused portion of the Permian Transmission Credit facility	$ 66,000,000
Credit Agreement | Standby Letters of Credit
Line of Credit Facility [Line Items]
Letters of credit	$ 2,000,000
LIBOR | Credit Agreement
Line of Credit Facility [Line Items]
Applicable margin (as a percent)	2.375%
Commitment fee (as a percent)	0.70%
Term Loan Credit Facility | Credit Agreement
Line of Credit Facility [Line Items]
Borrowing capacity		160,000,000
Working Capital Credit Facility | Credit Agreement
Line of Credit Facility [Line Items]
Borrowing capacity		$ 15,000,000

DEBT - Senior Notes (Narrative)

DEBT - Senior Notes (Narrative) (Details) - USD ($) $ in Millions	Apr. 15, 2023	Nov. 02, 2021	Sep. 30, 2021
2022 Senior Note | Subsequent Event
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount		100.00%
2025 Senior Notes
Debt Instrument [Line Items]
Deferred issuance costs			$ 7.7
Summit Holdings And Finance Corporation | 2025 Senior Notes
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount			102.875%
Summit Holdings And Finance Corporation | 2025 Senior Notes | Forecast
Debt Instrument [Line Items]
Redemption price, expressed as percentage of principal amount	100.00%

LIABILITY MANAGEMENT TRANSACT_3

LIABILITY MANAGEMENT TRANSACTIONS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				$ 1,389
Gain on early extinguishment of debt	$ 0	$ 24,690	$ 0	78,925
Open Market Repurchases
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				82,900
Gain on early extinguishment of debt				56,200
Debt Tender Offers
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				48,700
Gain on early extinguishment of debt				23,300
2022 Senior Note
Extinguishment of Debt [Line Items]
Extinguishment of debt, amount				210,800
2022 Senior Note | Open Market Repurchases
Extinguishment of Debt [Line Items]
Extinguishment of debt, amount				32,400
Total cash consideration paid for extinguishment				105
Gain on early extinguishment of debt				11,306
2022 Senior Note | Debt Tender Offers
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				465
Gain on early extinguishment of debt				8,633
Repurchase of senior notes				33,500
2025 Senior Notes
Extinguishment of Debt [Line Items]
Extinguishment of debt, amount				210,800
2025 Senior Notes | Open Market Repurchases
Extinguishment of Debt [Line Items]
Extinguishment of debt, amount				106,200
Total cash consideration paid for extinguishment				105
Gain on early extinguishment of debt				44,933
2025 Senior Notes | Debt Tender Offers
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				465
Gain on early extinguishment of debt				14,663
Repurchase of senior notes				$ 38,700

LIABILITY MANAGEMENT TRANSACT_4

LIABILITY MANAGEMENT TRANSACTIONS - Schedule of Gain (Loss) on Extinguishment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				$ 82,259
Payments of Debt Issuance Costs				(1,945)
Total cash consideration paid for extinguishment				(1,389)
Gain on early extinguishment of debt	$ 0	$ 24,690	$ 0	78,925
ECP Loan Repayment
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				0
Payments of Debt Issuance Costs				(361)
Total cash consideration paid for extinguishment				(249)
Gain on early extinguishment of debt				(610)
Open Market Repurchases
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				(82,900)
Gain on early extinguishment of debt				56,200
Open Market Repurchases | 2022 Senior Note
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				11,554
Payments of Debt Issuance Costs				(143)
Total cash consideration paid for extinguishment				(105)
Gain on early extinguishment of debt				11,306
Open Market Repurchases | 2025 Senior Notes
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				46,003
Payments of Debt Issuance Costs				(965)
Total cash consideration paid for extinguishment				(105)
Gain on early extinguishment of debt				44,933
Debt Tender Offers
Extinguishment of Debt [Line Items]
Total cash consideration paid for extinguishment				(48,700)
Gain on early extinguishment of debt				23,300
Debt Tender Offers | 2022 Senior Note
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				9,223
Payments of Debt Issuance Costs				(125)
Total cash consideration paid for extinguishment				(465)
Gain on early extinguishment of debt				8,633
Debt Tender Offers | 2025 Senior Notes
Extinguishment of Debt [Line Items]
Gain (Loss) on Repurchase of Debt Instrument				15,479
Payments of Debt Issuance Costs				(351)
Total cash consideration paid for extinguishment				(465)
Gain on early extinguishment of debt				$ 14,663

FINANCIAL INSTRUMENTS - Fair va

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
2022 Senior Notes | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 233,550	$ 233,188
2022 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	228,683	215,713
2025 Senior Notes | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	257,464	257,138
2025 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 235,030	$ 168,002

FINANCIAL INSTRUMENTS - Narrati

FINANCIAL INSTRUMENTS - Narrative (Details) $ in Millions	Sep. 30, 2021USD ($)
Concentration Risk [Line Items]
Fair value, other assets	$ 1.9
Interest Rate Swap
Concentration Risk [Line Items]
Derivative liability, notional amount	$ 144

PARTNERS' CAPITAL AND MEZZANI_3

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Schedule of Units (Details) - Common Units - shares	1 Months Ended	9 Months Ended
	Jul. 31, 2020	Sep. 30, 2021
Increase (Decrease) in Partners' Capital [Roll Forward]
Units, beginning balance (in shares)		6,110,092
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes (in shares)	62,816	538,715
Common units issued for SMLP LTIP, net (in shares)		106,580
ECP Warrant exercise (in shares)		414,447
Units, ending balance (in shares)		7,169,834

PARTNERS' CAPITAL AND MEZZANI_4

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	May 28, 2020	May 27, 2020	Jul. 31, 2020	Sep. 30, 2021	Aug. 05, 2021	Apr. 15, 2021	Dec. 31, 2020	Dec. 31, 2017
Partners Capital [Line Items]
Maximum period following end of quarter to distribute all available cash				45 days
Common Units
Partners Capital [Line Items]
Series A Preferred Unit Exchange Offer, net of shares withheld for taxes (in shares)			62,816	538,715
Common Units
Partners Capital [Line Items]
Common units issued in exchange (in shares)					414,447
Common Units | GP Buy-In
Partners Capital [Line Items]
Number of common units purchased (in shares)	537,307	8,059,609
Common Units | ECP Holdings Warrant | GP Buy-In
Partners Capital [Line Items]
Number of common units purchased (in shares)	129,360	1,940,391
Subsidiary Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued (in shares)				89,866,000			85,308,000
Subsidiary Series A preferred unitholders, outstanding (in shares)				89,866,000			85,308,000
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued (in shares)			817,845			18,662		300,000
Interest in partnership per unit (in dollars per share)								$ 1,000
Accrued and unpaid distributions				$ 26,000
PIK distributions				4,558
Redemption amount				$ 112,300

PARTNERS' CAPITAL AND MEZZANI_5

PARTNERS' CAPITAL AND MEZZANINE CAPITAL- Change in Subsidiary (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Series A Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Redemption accretion	$ 7,716	$ 5,856
Series A Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning balance	89,658
PIK distributions	4,558
Ending balance	$ 101,932

EARNINGS PER UNIT (Details)

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 7,004		$ 25,629	$ (3,744)	$ 86,112
Net loss attributable to noncontrolling interest	0		0	0	3,274
Net income (loss) attributable to Summit Midstream Partners, LP	2,751		18,331	(16,018)	79,746
Add: deemed contribution from Preferred Exchange Offer	$ 0	$ 8,300	$ 54,945	$ 8,326	$ 54,945
Common unit - basic (in dollars per share)	$ (0.17)		$ 19.28	$ (2.99)	$ 36.12
Common unit - diluted (in dollars per share)	$ (0.17)		$ 18.67	$ (2.99)	$ 35.04
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU (in shares)	367		269	193	224
Series A Preferred Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ (3,916)		$ (6,481)	$ (12,052)	$ (20,731)
Series A Preferred Units | Subsidiaries
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	(4,253)		(7,298)	(12,274)	(9,640)
Common Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ (1,165)		$ 66,795	$ (19,744)	$ 113,960
Weighted-average common units outstanding – basic (in shares)	6,999,000		3,465,000	6,596,000	3,155,000
Effect of nonvested phantom units (in shares)	0		112,000	0	97,000
Weighted-average common units outstanding – diluted (in shares)	6,999,000		3,577,000	6,596,000	3,252,000

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Supplemental cash flow information:
Cash interest paid	$ 42,104
Cash paid for taxes	191	$ 0
Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	5,614	10,233
Warrant issuance for GP Buy-In Transaction	0	2,300
Right-of-use assets relating to ASC Topic 842	0	2,964
Exercise of ECP Warrants	15,542	0
Series A Preferred Units
Noncash investing and financing activities:
Accretion of Subsidiary Series A Preferred Units	$ 7,716	$ 5,856

UNIT-BASED AND NONCASH COMPEN_2

UNIT-BASED AND NONCASH COMPENSATION (Details) - SMLP LTIP	9 Months Ended
	Sep. 30, 2021director$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units remaining available (in shares)	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
Common Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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 - Schedule of Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 2,929
Payments made	(1,039)
Additional accruals	3,718
Accrued environmental remediation, ending balance	$ 5,608

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Dec. 31, 2020	Sep. 30, 2021
Loss Contingencies [Line Items]
Legal fines and other fees		$ 36,300
2015 Blacktail Release
Loss Contingencies [Line Items]
Loss contingency in period	$ 17,000
Increase in loss contingency accrual		19,300
Loss contingency accrual		$ 36,300
Unpaid penalties and fines, fixed rate (as a percent)		3.25%
Expected payment		$ 3,100
Natural Resource Damages To Federal and State Governments | 2015 Blacktail Release
Loss Contingencies [Line Items]
Legal fines and other fees		$ 1,250
Penalties and fines, payment period		5 years
Damages Payable To Federal Government over Five Years | 2015 Blacktail Release
Loss Contingencies [Line Items]
Legal fines and other fees		$ 25,000
Damages Payable To State Governments Over Six Years | 2015 Blacktail Release
Loss Contingencies [Line Items]
Legal fines and other fees		$ 10,000
Penalties and fines, payment period		6 years

RESTRUCTURING (Details)

RESTRUCTURING (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Accrued and unpaid liabilities	$ 15,369		$ 15,369		$ 13,036
2020 Restructuring Activities
Restructuring Cost and Reserve [Line Items]
Restructuring costs	100		900
Accrued and unpaid liabilities	200		200
2019 Restructuring Activities
Restructuring Cost and Reserve [Line Items]
Restructuring costs		$ 100		$ 3,400
2019 Restructuring Activities | Maximum
Restructuring Cost and Reserve [Line Items]
Accrued and unpaid liabilities	$ 100		$ 100

SEGMENT INFORMATION - Assets, R

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 2,500,677	$ 2,499,817
Equity method investment	481,985	392,740
Double E
Segment Reporting Information [Line Items]
Equity method investment	233,612	132,852
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,258,284	2,353,741
Reportable Segments | Utica Shale
Segment Reporting Information [Line Items]
Assets	208,715	209,425
Reportable Segments | Ohio Gathering
Segment Reporting Information [Line Items]
Assets	248,373	259,888
Reportable Segments | Williston Basin
Segment Reporting Information [Line Items]
Assets	407,593	425,873
Reportable Segments | DJ Basin
Segment Reporting Information [Line Items]
Assets	193,471	199,920
Reportable Segments | Permian Basin
Segment Reporting Information [Line Items]
Assets	165,935	165,765
Reportable Segments | Piceance Basin
Segment Reporting Information [Line Items]
Assets	541,465	579,800
Reportable Segments | Barnett Shale
Segment Reporting Information [Line Items]
Assets	320,984	336,629
Reportable Segments | Marcellus Shale
Segment Reporting Information [Line Items]
Assets	171,748	176,441
Corporate and Other
Segment Reporting Information [Line Items]
Assets	$ 242,393	$ 146,076

SEGMENT INFORMATION - Adjusted

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 68,546	$ 66,684	$ 202,417	$ 214,105
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	8,328	7,453	26,700	24,074
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,690	7,129	20,403	22,582
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	11,276	11,713	31,707	40,632
DJ Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	7,446	4,766	17,899	15,016
Permian Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	559	893	1,729	4,302
Piceance Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	18,908	21,503	60,266	66,794
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	9,637	7,205	26,542	24,475
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 5,702	$ 6,022	$ 17,171	$ 16,230

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Net Income (Loss) to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting [Abstract]
Income (loss) before income taxes and equity method investment income	$ 4,850	$ 25,132	$ (10,779)	$ 78,862
Add:
Corporate and Other expense	10,895	6,874	58,953	28,484
Interest expense	15,530	19,018	44,985	64,836
Gain on early extinguishment of debt	0	(24,690)	0	(78,925)
Depreciation and amortization	31,226	29,739	88,570	89,505
Proportional adjusted EBITDA for equity method investees	6,690	7,129	20,403	22,582
Adjustments related to MVC shortfall payments	0	2,292	0	(859)
Adjustments related to capital reimbursement activity	(1,549)	(328)	(5,019)	(776)
Unit-based and noncash compensation	868	1,622	3,883	6,191
Gain on asset sales, net	(212)	(104)	(352)	(270)
Long-lived asset impairments	248	0	1,773	4,475
Total of reportable segments' measures of profit	$ 68,546	$ 66,684	$ 202,417	$ 214,105

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Subsequent Event	Nov. 02, 2021USD ($)
2026 Notes
Subsequent Event [Line Items]
Debt offering	$ 700,000,000
Stated interest rate (as a percent)	8.50%
Debt issued as a percent of face value	98.50%
2025 Senior Notes
Subsequent Event [Line Items]
Maximum amount of debt outstanding for maturity to occur	$ 50,000,000
2022 Senior Note
Subsequent Event [Line Items]
Redemption price, expressed as percentage of principal amount	100.00%
Secured Notes Indenture, 2026
Subsequent Event [Line Items]
Redemption price, expressed as percentage of principal amount	108.50%
Redemption percentage (as a percent)	35.00%
Redemption covenant, percent of initial principal amount remaining outstanding	65.00%
Ownership percentage of principal	25.00%
Secured Notes Indenture, 2026 | Beginning October 15, 2023
Subsequent Event [Line Items]
Redemption price, expressed as percentage of principal amount	104.25%
Secured Notes Indenture, 2026 | Beginning October 15, 2024
Subsequent Event [Line Items]
Redemption price, expressed as percentage of principal amount	102.125%
Secured Notes Indenture, 2026 | Beginning October 15, 2025
Subsequent Event [Line Items]
Redemption price, expressed as percentage of principal amount	100.00%
ABL Facility
Subsequent Event [Line Items]
Debt offering	$ 400,000,000
Maximum amount of debt outstanding for maturity to occur	$ 50,000,000
Partners' leverage ratio	2.50
Interest coverage ratio	2