Summit Midstream Partners (SMLP) 10-Q 6 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Sep. 30, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		56,624,887
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Title of 12(b) Security	Common Units
Trading Symbol	SMLP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-35666
Entity Tax Identification Number	45-5200503
Entity Address, Address Line One	910 Louisiana Street
Entity Address, Address Line Two	Suite 4200
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	832
Local Phone Number	413-4770
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Document Transition Report	false
Entity Incorporation, State or Country Code	DE

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
ASSETS
Cash and cash equivalents	$ 50,272	$ 9,530
Restricted cash	24	27,392
Accounts receivable, net	76,497	97,418
Other current assets	4,559	5,521
Total current assets	131,352	139,861
Property, plant and equipment, net	1,840,284	1,882,489
Intangible assets, net	207,766	232,278
Investment in equity method investees	389,088	309,728
Other noncurrent assets	4,989	9,742
TOTAL ASSETS	2,573,479	2,574,098
LIABILITIES AND CAPITAL
Trade accounts payable	16,205	24,415
Accrued expenses	11,353	11,339
Deferred revenue	17,827	13,493
Ad valorem taxes payable	6,931	8,477
Accrued interest	12,092	12,346
Accrued environmental remediation	1,553	1,725
Other current liabilities	10,747	12,206
Term loan (See TL Restructuring discussion in Note 8)	155,200	5,546
Total current liabilities	231,908	89,547
Long-term debt	1,390,842	1,622,279
Noncurrent deferred revenue	41,755	38,709
Noncurrent accrued environmental remediation	2,003	2,926
Other noncurrent liabilities	4,536	7,951
Total liabilities	1,671,044	1,761,412
Commitments and contingencies (Note 14)
Mezzanine Capital
Subsidiary Series A Preferred Units (83,842 and 30,058 units issued and outstanding at September 30, 2020 and December 31, 2019, respectively)	85,800	27,450
Partners' Capital
Series A Preferred Units (237,184 and 300,000 units issued and outstanding at September 30, 2020 and December 31, 2019, respectively)	249,351	293,616
Common limited partner capital (56,624,887 and 45,318,866 units issued and outstanding at September 30, 2020 and December 31, 2019, respectively)	567,284	305,550
Noncontrolling interest		186,070
Total partners' capital	816,635	785,236
TOTAL LIABILITIES AND CAPITAL	$ 2,573,479	$ 2,574,098

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2020	Dec. 31, 2019
Subsidiary Series A preferred unitholders, issued	237,184	300,000
Subsidiary Series A preferred unitholders, outstanding	237,184	300,000
Common limited partner capital (in shares), issued	56,624,887	45,318,866
Common limited partner capital (in shares), outstanding	56,624,887	45,318,866
Mezzanine Capital
Subsidiary Series A preferred unitholders, issued	83,842	30,058
Subsidiary Series A preferred unitholders, outstanding	83,842	30,058

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues		$ 90,153	$ 100,187	$ 287,063	$ 331,281
Costs and expenses:
Cost of natural gas and NGLs		8,632	7,472	22,945	50,802
Operation and maintenance		22,168	26,231	65,131	74,771
General and administrative		10,561	10,029	39,908	38,979
Depreciation and amortization		29,505	27,443	88,801	82,044
Transaction costs		726	129	1,944	2,562
Gain on asset sales, net		(104)	(347)	(270)	(1,595)
Long-lived asset impairment				4,475	45,021
Goodwill impairment			16,211	0	16,211
Total costs and expenses		71,488	87,168	222,934	308,795
Other income		795	12	644	304
Interest expense		(19,018)	(23,462)	(64,836)	(68,547)
Gain on early extinguishment of debt		24,690		78,925	0
Income (loss) before income taxes and equity method investment income (loss)		25,132	(10,431)	78,862	(45,757)
Income tax benefit (expense)		(298)	(21)	104	(1,427)
Income (loss) from equity method investees		795	(677)	7,146	(1,197)
Net income (loss)		25,629	(11,129)	86,112	(48,381)
Net income (loss) attributable to noncontrolling interest			(10,340)	(3,274)	(37,251)
Net income (loss) attributable to limited partners		25,629	(789)	89,386	(11,130)
Deemed contribution on exchange of preferred units		54,945		54,945
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners		6,481	7,125	20,731	21,375
Deemed contribution on exchange of preferred units		54,945		54,945
Series A Preferred Units | Subsidiaries
Costs and expenses:
Net income (loss) attributable to limited partners		7,298		9,640
Common Units
Costs and expenses:
Net income (loss) attributable to limited partners		$ 66,795	$ (7,914)	$ 113,960	$ (32,505)
Net income (loss) per limited partner unit:
Basic (in dollars per share)		$ 1.29	$ (0.17)	$ 2.41	$ (0.72)
Diluted (in dollars per share)		$ 1.25	$ (0.17)	$ 2.34	$ (0.72)
Weighted-average limited partner units outstanding:
Basic (shares)	[1]	51,974	45,319	47,331	45,319
Diluted (shares)		53,650	45,319	48,782	45,319
Natural Gas, Gathering, Transportation, Marketing and Processing
Revenues:
Total revenues		$ 71,964	$ 80,968	$ 229,667	$ 243,039
Oil and Condensate
Revenues:
Total revenues		10,783	12,219	35,246	68,438
Product and Service, Other
Revenues:
Total revenues		$ 7,406	$ 7,000	$ 22,150	$ 19,804
[1]	As a result of the GP Buy-In Transaction, our historical results are those of Summit Investments. The number of common units of 45.3 million as of September 30, 2019 represents those of Summit Investments and has been used for the earnings per unit calculations presented herein.

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Partners' Capital	Partners' CapitalSeries A Preferred Units	Noncontrolling InterestSeries A Preferred Units	Noncontrolling InterestCommon Noncontrolling Interest	[1]
Beginning balance at Dec. 31, 2018	$ 1,391,567	$ 543,479		$ 293,616	$ 554,472
Net income (loss)	(40,280)	(21,835)		7,125	(25,570)
Net cash distributions to SMLP unitholders	(27,374)				(27,374)
Unit-based compensation	2,526				2,526
Effect of common unit issuances under SMLP LTIP		(2,387)			2,387
Tax withholdings and associated payments on vested SMLP LTIP awards	(2,524)				(2,524)
Conversion of noncontrolling interest related to cancellation of subsidiary incentive distribution rights		48,203			(48,203)
Ending balance at Mar. 31, 2019	1,323,915	567,460		300,741	455,714
Net income (loss)	3,028	(2,756)		7,125	(1,341)
Net cash distributions to SMLP unitholders	(28,076)			(14,250)	(13,826)
Net cash distributions to Energy Capital Partners	(68,984)	(68,984)
Unit-based compensation	1,393				1,393
Effect of common unit issuances under SMLP LTIP		(40)			40
Tax withholdings and associated payments on vested SMLP LTIP awards	(93)				(93)
Ending balance at Jun. 30, 2019	1,231,183	495,680		293,616	441,887
Net income (loss)	(11,129)	(7,914)		7,125	(10,340)
Net cash distributions to SMLP unitholders	(13,829)				(13,829)
Unit-based compensation	1,451				1,451
Effect of common unit issuances under SMLP LTIP		(173)			173
Tax withholdings and associated payments on vested SMLP LTIP awards	55				55
Ending balance at Sep. 30, 2019	1,207,731	487,593		300,741	419,397
Beginning balance at Dec. 31, 2019	785,236	305,550		293,616	186,070
Net income (loss)	2,817	(2,427)		7,125	(1,881)
Net cash distributions to SMLP unitholders	(6,037)				(6,037)
Unit-based compensation	2,723				2,723
Effect of common unit issuances under SMLP LTIP		(2,322)			2,322
Tax withholdings and associated payments on vested SMLP LTIP awards	(984)				(984)
Ending balance at Mar. 31, 2020	783,755	300,801		300,741	182,213
Beginning balance at Dec. 31, 2019	785,236	305,550		293,616	186,070
Conversion of noncontrolling interest related to cancellation of subsidiary incentive distribution rights	54,945
Ending balance at Sep. 30, 2020	816,635	567,284	$ 249,351
Beginning balance at Mar. 31, 2020	783,755	300,801		300,741	182,213
Net income (loss)	55,324	49,592	2,375	4,750	(1,393)
Unit-based compensation	1,846	515			1,331
Tax withholdings and associated payments on vested SMLP LTIP awards	(62)	(28)			(34)
GP Buy-In Transaction assumption of noncontrolling interest in SMLP		182,117	305,491	$ (305,491)	$ (182,117)
Repurchase of common units under GP Buy-In Transaction	(44,078)	(44,078)
Other	(61)	(61)
Ending balance at Jun. 30, 2020	796,724	488,858	307,866
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 Series A Preferred Unit Exchange	(237)	(237)
Conversion of Series A Preferred Units to SMLP common units inclusive of a $54.9 million deemed contribution to common unit holders (Note 10)		64,996	(64,996)
Other	312	312
Conversion of noncontrolling interest related to cancellation of subsidiary incentive distribution rights	54,945
Ending balance at Sep. 30, 2020	$ 816,635	$ 567,284	$ 249,351
[1]	Prior to the GP Buy-In Transaction, common noncontrolling interests reported by Summit Investments included equity interests in SMLP that were not owned by Summit Investments.

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Statement Of Partners Capital [Abstract]
Deemed contribution on exchange of preferred units	$ 54,945	$ 54,945

UNAUDITED CONDENSED CONSOLIDA_6

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income (loss)	$ 86,112	$ (48,381)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	89,505	83,030
Noncash lease expense	1,925	2,299
Amortization of debt issuance costs	4,870	4,719
Unit-based and noncash compensation	6,191	5,370
(Income) loss from equity method investees	(7,146)	1,197
Distributions from equity method investees	19,859	28,008
Gain on asset sales, net	(270)	(1,595)
Gain on early extinguishment of debt	(78,925)	0
Gain on fair value of warrants	(838)	0
Long-lived asset impairment	4,475	45,021
Goodwill impairment	0	16,211
Changes in operating assets and liabilities:
Accounts receivable	20,922	8,363
Trade accounts payable	470	820
Accrued expenses	(1,078)	(11,965)
Deferred revenue, net	7,379	1,910
Ad valorem taxes payable	(1,546)	(2,061)
Accrued interest	2,680	3,065
Accrued environmental remediation, net	(1,368)	(2,025)
Other, net	(6,410)	(6,369)
Net cash provided by operating activities	146,807	127,617
Cash flows from investing activities:
Capital expenditures	(35,312)	(151,663)
Proceeds from asset sale (net of cash of $1,475 for the period ended September 30, 2019)	0	90,111
Distribution from equity method investment	0	7,252
Investment in equity method investee	(92,072)	(11,330)
Other, net	2,486	343
Net cash used in investing activities	(124,898)	(65,287)
Cash flows from financing activities:
Net cash distributions to noncontrolling interest SMLP unitholders	(6,037)	(55,029)
Series A Preferred Unit distributions	0	(14,250)
Net cash distributions to Energy Capital Partners	0	(68,984)
Borrowings under Revolving Credit Facility	165,500	265,000
Repayments on Revolving Credit Facility	(34,000)	(131,000)
Repayments on SMPH Term Loan	(6,300)	(59,500)
Proceeds from issuance of Subsidiary Series A preferred units, net of issuance costs	48,710	0
Borrowings under ECP Loans (Note 8)	35,000	0
Repayment of ECP Loans (Note 8)	(35,000)	0
Purchase of common units in GP Buy-In Transaction	(41,778)	0
Debt issuance costs	(835)	(584)
Proceeds from asset sale	288	0
Other, net	(2,527)	(3,930)
Net cash provided by (used in) financing activities	(8,535)	(68,277)
Net change in cash, cash equivalents and restricted cash	13,374	(5,947)
Cash, cash equivalents and restricted cash, beginning of period	36,922	16,173
Cash, cash equivalents and restricted cash, end of period	50,296	10,226
Open Market Repurchases
Cash flows from financing activities:
Repurchases of 2022 and 2025 Senior Notes (Note 8)	(82,844)	0
Tender Offers
Cash flows from financing activities:
Repurchases of 2022 and 2025 Senior Notes (Note 8)	$ (48,712)	$ 0

ORGANIZATION, BUSINESS OPERATIO

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION	1. ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION Organization. SMLP, a Delaware limited partnership, 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. Our business activities are conducted through various operating subsidiaries, each of which is owned or controlled by our wholly owned subsidiary holding company, Summit Holdings, a Delaware limited liability company. References to the "Partnership," "we," or "our" refer collectively to SMLP and its subsidiaries. On May 28, 2020, the Partnership closed the transactions contemplated by the Purchase Agreement (the “Purchase Agreement”), dated May 3, 2020, with affiliates of its then private equity sponsor, Energy Capital Partners II, LLC (“ECP”), to acquire Summit Midstream Partners, LLC (“Summit Investments”). The purchase of Summit Investments resulted in the Partnership acquiring an indirect ownership interest in Summit Midstream Partners Holdings, LLC, a Delaware limited liability company (“SMP Holdings”), which in turn owned (a) 34,604,581 SMLP common units representing limited partner interests in the Partnership (the “common units”) that were pledged as collateral under the SMPH Term Loan, (b) 10,714,285 SMLP common units that were not pledged as collateral under the SMPH Term Loan and (c) a deferred purchase price obligation receivable owed by the Partnership. In addition, the Partnership acquired 5,915,827 SMLP common units held by an affiliate of ECP. The total purchase price was $35.0 million in cash and warrants to purchase up to 10 million SMLP common units (refer to Note 11 – Partners’ Capital and Mezzanine Capital for additional details). Pursuant to the Purchase Agreement, the Partnership, through its indirect ownership interest of SMP Holdings, will retain any liabilities stemming from the release of produced water from a produced water pipeline operated by Meadowlark Midstream Company, LLC, a subsidiary of the Partnership, that occurred near Williston, North Dakota and was discovered on January 6, 2015. These transactions are collectively referred to as the “GP Buy-In Transaction.” As a result of the GP Buy-In Transaction, the Partnership indirectly owns its General Partner. Following the closing of the GP Buy-In Transaction, the Partnership retired 16,630,112 SMLP common units it acquired that are not pledged as collateral under the SMPH Term Loan. The 34,604,581 SMLP common units that are pledged as collateral under the SMPH Term Loan are not considered outstanding with respect to voting and distributions under the Partnership Agreement so long as they are held by a subsidiary of the Partnership. 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. Presentation and Consolidation. The condensed consolidated financial statements contained in this report include all normal and recurring material adjustments that, in the opinion of management, are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented herein. The accompanying condensed consolidated financial statements were prepared using GAAP for interim financial information and in accordance with the rules and regulations of the Securities and Exchange Commission. As permitted under those rules, certain information relating to the Partnership’s organization and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been appropriately condensed or omitted. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and the notes thereto included in the Partnership ’s Annual Report for the year ended December 31, 2019 (“2019 Annual Report”). The Partnership believes the disclosures made are adequate to make the information presented not misleading . Risks and Uncertainties. The Partnership is closely monitoring the impact of the outbreak of COVID-19 on all aspects of its business, including how it has impacted and will impact its customers, employees, supply chain and distribution network. While COVID-19 did not have a material adverse effect on the Partnership’s reported results for the first nine months of 2020, the Partnership is unable to predict the ultimate impact that COVID-19 may have on its business, future results of operations, financial position or cash flows. Given the dynamic nature of the COVID-19 pandemic and related market conditions, the Partnership cannot reasonably estimate the period of time that these events will persist or the full extent of the impact they will have on its business. The full extent to which the Partnership’s operations may be impacted by the COVID-19 pandemic will depend largely on future developments, which are highly uncertain and cannot be accurately predicted, including changes in the severity of the pandemic, countermeasures taken by governments, businesses and individuals to slow the spread of the pandemic, and the ability of pharmaceutical companies to develop effective and safe vaccines and therapeutic drugs. Furthermore, the impacts of a potential worsening of global economic conditions and the continued disruptions to and volatility in the financial markets remain unknown.

SUMMARY OF RECENTLY ISSUED ACCO

SUMMARY OF RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
SUMMARY OF RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP	2. SUMMARY OF RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. The Partnership reviews new pronouncements to determine the impact, if any, on its financial statements. Accounting standards that have or could possibly have a material effect on the Partnership’s financial statements are discussed below. Recently Adopted Accounting Pronouncements . The Partnership recently adopted the following accounting pronouncements: • 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 condensed 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 condensed consolidated financial statements or disclosures. Accounting Pronouncements Not Yet Adopted . The Partnership has not yet adopted the following accounting pronouncements as of September 30, 2020: • ASU No. 2020-06 Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815 – 40) (“ASU 2020-06”). ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. The ASU is part of the FASB’s simplification initiative, which aims to reduce unnecessary complexity in U.S. GAAP. The ASU’s amendments are effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years. The Partnership is currently evaluating the provisions of ASU 2020-06 to determine its impact on the Partnership’s condensed consolidated financial statements and disclosures. • ASU No. 2020-04 Reference Rate Reform (“ASU 2020-04”). ASU 2020-04 provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform on financial reporting. The amendments in ASU 2020-04 are effective as of March 12, 2020 through December 31, 2022. The Partnership is currently evaluating the provisions of ASU 2020-04 to determine its impact on the Partnership’s condensed consolidated financial statements and disclosures.

REVENUE

REVENUE	9 Months Ended
	Sep. 30, 2020
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 2020 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments. 2020 2021 2022 2023 2024 Thereafter (In thousands) Gathering services and related fees $ 29,678 $ 102,127 $ 84,736 $ 66,693 $ 50,608 $ 56,912 Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 16 – Segment Information. 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 All other segments — — 644 644 Total $ 71,964 $ 10,783 $ 7,406 $ 90,153 Three months ended September 30, 2019 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,865 $ - $ - $ 8,865 Williston Basin 16,685 1,878 2,555 21,118 DJ Basin 7,039 93 735 7,867 Permian Basin 986 3,797 102 4,885 Piceance Basin 30,120 1,733 1,258 33,111 Barnett Shale 11,286 4,828 1,706 17,820 Marcellus Shale 5,987 — — 5,987 Total reportable segments 80,968 12,329 6,356 99,653 All other segments — (110 ) 644 534 Total $ 80,968 $ 12,219 $ 7,000 $ 100,187 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 All other segments — — 1,931 1,931 Total $ 229,667 $ 35,246 $ 22,150 $ 287,063 Nine months ended September 30, 2019 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 23,951 $ - $ - $ 23,951 Williston Basin 58,076 11,231 8,133 77,440 DJ Basin 14,784 279 2,776 17,839 Permian Basin 1,938 10,424 183 12,545 Piceance Basin 92,515 6,139 3,341 101,995 Barnett Shale 35,739 11,705 5,008 52,452 Marcellus Shale 18,081 — — 18,081 Total reportable segments 245,084 39,778 19,441 304,303 All other segments (2,045 ) 28,660 363 26,978 Total $ 243,039 $ 68,438 $ 19,804 $ 331,281 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 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: September 30, 2020 (In thousands) Contract assets, January 1, 2020 $ 3,902 Additions 16,442 Transfers out (2,275 ) Contract assets, September 30, 2020 $ 18,069 As of September 30, 2020, receivables with customers totaled $53.8 million and contract assets totaled $18.1 million and are included in the accounts receivable caption on the unaudited condensed consolidated balance sheets. As of December 31, 2019, receivables with customers totaled $90.4 million and contract assets totaled $3.9 million and 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, 2020 and 2019, the Partnership recognized $2.4 million and $2.4 million of gathering services and related fees, respectively, which are included in the contract liability balance as of the beginning of the period. For the nine months ended September 30, 2020 and 2019, the Partnership recognized $7.1 million and $7.8 million of gathering services and related fees, respectively, which are included in the contract liability balance at the beginning of the period. See Note 7 – Deferred Revenue for additional details.

PROPERTY, PLANT, AND EQUIPMENT,

PROPERTY, PLANT, AND EQUIPMENT, NET	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT, NET	4. PROPERTY, PLANT AND EQUIPMENT, NET Details on property, plant and equipment follow. September 30, 2020 December 31, 2019 (In thousands) Gathering and processing systems and related equipment $ 2,197,087 $ 2,182,950 Construction in progress 78,146 78,716 Land and line fill 10,440 10,137 Other 60,589 54,595 Total 2,346,262 2,326,398 Less accumulated depreciation (505,978) (443,909) Property, plant and equipment, net $ 1,840,284 $ 1,882,489 In March 2020, in connection with the cancellation of a compressor station project in the DJ Basin due to delays in customer drilling plans, the Partnership recorded an impairment charge of $3.6 million for the related soft project costs. In March 2019, certain events occurred which indicated that certain long-lived assets in the DJ Basin and Barnett Shale reporting segments could be impaired. Consequently, in the first quarter of 2019, the Partnership performed a recoverability assessment of certain assets within these reporting segments, the results of which are described below. In March 2019, the Partnership determined that certain processing plant assets in the DJ Basin related to its existing 20 MMcf/d plant would no longer be utilized due to the Partnership’s expansion plans for the Niobrara G&P system. Based on the results of the recoverability assessment and the conclusion that the carrying value was not fully recoverable, the Partnership recorded an impairment charge of $34.7 million related to these assets in the first quarter of 2019. In March 2019, the Partnership determined that certain compressor station assets in the Barnett Shale were impaired and recorded an impairment charge of $10.2 million, comprised of a $9.7 million impairment of fixed assets and a $0.5 million impairment of rights-of-way. Depreciation expense and capitalized interest follow. Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (In thousands) Depreciation expense $ 21,537 $ 19,474 $ 64,899 $ 58,160 Capitalized interest 1,449 1,391 2,268 5,752

GOODWILL

GOODWILL	9 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
GOODWILL	5. GOODWILL Goodwill. The Partnership evaluates goodwill for impairment annually on September 30 th Fair Value Measurement. The Partnership’s impairment determinations, in the context of (i) its annual impairment evaluations and (ii) its other-than-annual impairment evaluations, involve significant assumptions and judgments, as discussed in the 2019 Annual Report. Differing assumptions regarding any of these inputs could have a significant effect on the valuations. As such, the fair value measurements utilized within these models are classified as non-recurring Level 3 measurements in the fair value hierarchy because they are not observable from objective sources.

EQUITY METHOD INVESTMENTS

EQUITY METHOD INVESTMENTS	9 Months Ended
	Sep. 30, 2020
Equity Method Investments And Joint Ventures [Abstract]
EQUITY METHOD INVESTMENTS	6. EQUITY METHOD INVESTMENTS Double E The Partnership is responsible for leading the development, permitting and construction of the Double E Project. During the three and nine month periods ended September 30, 2020, the Partnership made cash investments of $12.4 million and $92.1 million, respectively, in the Double E Project. For the three and nine months ended September 30, 2020, other than the investment activity noted above, Double E did not have any results of operations given that the Double E Project is currently under development. Ohio Gathering As of September 30, 2020 and December 31, 2019, the Partnership’s ownership interest in Ohio Gathering was 38.2% and 38.5%, respectively, and provided below is the September 30, 2020 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 (in thousands). Investment in Ohio Gathering, September 30, 2020 $ 263,639 September cash distributions 3,870 Basis difference 218,757 Investment in Ohio Gathering (Books and records), August 31, 2020 $ 486,266

DEFERRED REVENUE

DEFERRED REVENUE	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
DEFERRED REVENUE	7. DEFERRED REVENUE A rollforward of current deferred revenue follows. Total (In thousands) Current deferred revenue, January 1, 2020 $ 13,493 Additions 15,433 Less: revenue recognized (11,099) Current deferred revenue, September 30, 2020 $ 17,827 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2020 $ 38,709 Additions 18,402 Less: reclassification to current deferred revenue (15,356) Noncurrent deferred revenue, September 30, 2020 $ 41,755

DEBT

DEBT	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
DEBT	8. DEBT Debt consisted of the following: September 30, 2020 December 31, 2019 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured Revolving Credit Facility (2.90% at September 30, 2020 and 4.55% at December 31, 2019) due May 2022 $ 808,500 $ 677,000 ECP Loans : Summit Holdings' 8.00% senior secured term loans due March 2021 — — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 2022 234,047 300,000 Less: unamortized debt issuance costs (1) (997 ) (1,686 ) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 2025 355,071 500,000 Less: unamortized debt issuance costs (1) (3,055 ) (5,015 ) SMPH Term Loan : SMP Holdings' variable rate senior secured term loan (7.00% at September 30, 2020 and 7.80% at December 31, 2019) due May 2022 155,200 161,500 Less: unamortized debt issuance costs (1) (2,724 ) (3,974 ) Total debt 1,546,042 1,627,825 Less: current portion (155,200) (5,546) Total long-term debt $ 1,390,842 $ 1,622,279 (1) Revolving Credit Facility. The Partnership’s subsidiary, Summit Holdings, has a senior secured revolving credit facility (the “Revolving Credit Facility”) which allows for revolving loans, letters of credit and swingline loans. The Revolving Credit Facility has a $1.25 billion borrowing capacity, matures in May 2022, and includes a $250.0 million accordion feature. At September 30, 2020, the applicable margin under LIBOR borrowings was 2.75%, the interest rate was 2.90% and the unused portion of the Revolving Credit Facility totaled $437.4 million, subject to a commitment fee of 0.50%, after giving effect to the issuance thereunder of a $4.1 million outstanding but undrawn irrevocable standby letter of credit. Based on covenant limits, our available borrowing capacity under the Revolving Credit Facility as of September 30, 2020 was approximately $172.0 million. As of and during the nine months ended September 30, 2020, we were in compliance with the Revolving Credit Facility's financial covenants. There were no defaults or events of default during the nine months ended September 30, 2020. Significant updates to the Partnership’s indebtedness for the three and nine months ended September 30, 2020 included the following matters. ECP Loans . On May 28, 2020, in connection with the closing of the GP Buy-In Transaction, Summit Holdings, entered into (i) a Term Loan Credit Agreement (the “ECP NewCo Term Loan Credit Agreement”), with SMP TopCo, LLC, a Delaware limited liability company and affiliate of ECP (“ECP NewCo”), as lender and administrative agent, and Mizuho Bank (USA) (“Mizuho”), as collateral agent, in a principal amount of $28.2 million (the “ECP NewCo Loan”), and (ii) a Term Loan Credit Agreement (the “ECP Holdings Term Loan Credit Agreement” and together with the ECP NewCo Term Loan Credit Agreement, the “ECP Term Loan Credit Agreements”), with ECP Holdings, as lender, and ECP NewCo, as administrative agent and Mizuho, as collateral agent, in a principal amount of $6.8 million (the “ECP Holdings Loan” and together with the ECP NewCo Loan, the “ECP Loans”). The ECP Loans were set to mature on March 31, 2021 and bore interest at a rate of 8.00% per annum, with the interest payment due at maturity of the ECP Loans. With borrowings under the Partnership’s Revolving Credit Facility, the Partnership fully repaid all amounts outstanding under the ECP Loans ($35 million of principal and $0.6 million of accrued interest) on August 7, 2020. SMPH Term Loan. On April 17, 2020, the Partnership entered into a derivative financial instrument to convert a portion of its variable rate SMPH Term Loan to a fixed rate debt consisting of a 1% LIBOR interest rate cap for a fee of $0.2 million (exclusive of the applicable bank margin charged by our lender) on a $125.0 million notional amount beginning April 30, 2020 and ending on April 30, 2022 . The Partnership did not designate the interest rate cap for hedge accounting as defined by GAAP and recognized an unsettled gain of $0.1 million on the interest rate cap in the other income line item on our unaudited condensed consolidated statement of operations for the three and nine month periods ended September 30, 2020. 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. Open Market Repurchases . During the nine months ended September 30, 2020, the Partnership made a number of open market repurchases of its 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. Tender Offers In September 2020, the Partnership completed cash tender offers (the “Tender Offers”) to purchase a portion of the 2022 and 2025 Senior Notes. Upon concluding the Tender Offers, the Partnership 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. SMPH Term Loan Restructuring . On September 29, 2020, SMP Holdings and the Partnership entered into the Transaction Support Agreement (the “TSA”) with an ad hoc group of SMP Holdings’ lenders under the $155.2 million SMPH Term Loan (the “Term Loan Lenders”) that will result in a consensual debt discharge and restructuring transaction (the “TL Restructuring”) of the full amount owed under SMPH Term Loan in exchange for (i) a cash payment of $26.5 million to the Term Loan Lenders, (ii) the execution of a strict foreclosure by the collateral agent under the SMPH Term Loan for the benefit of the Term Loan Lenders on the 34.6 million SMLP common units pledged as collateral under the SMPH Term Loan, and (iii) the payment of certain fees and expenses by the Partnership. Upon consummation of the TL Restructuring, which is expected to occur during the quarterly period ended December 31, 2020, the SMPH Term Loan will be fully satisfied and cease to exist. Upon closing of the TL Restructuring the Partnership will recognize a gain equal to the difference between the face value of the cancelled debt and the fair value of the total consideration transferred, including unamortized debt issuance costs, and certain direct transaction costs related to the restructuring. As a result of the TL Restructuring, at September 30, 2020 the Partnership classified the SMPH Term Loan as current. Concurrently with the closing of the TL Restructuring, the Partnership will make a $26.5 million cash payment on the Deferred Purchase Price Obligation to SMP Holdings and fully settle the obligation. 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, primarily as the result of the its Open Market Repurchases and its Tender Offers. ECP Loan Repayment Open Market Repurchases Tender Offers Total 2022 2025 2022 2025 Senior Notes Senior Notes Senior Notes Senior Notes (in thousands) 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, 2020
Fair Value Disclosures [Abstract]
FINANCIAL INSTRUMENTS	9. FINANCIAL INSTRUMENTS Fair Value. A summary of the estimated fair value of our debt financial instruments follows. September 30, 2020 December 31, 2019 Carrying Value, Net Estimated fair value (Level 2) Carrying Value, Net Estimated fair value (Level 2) (In thousands) 2022 Senior Notes $ 233,050 $ 169,684 $ 298,314 $ 266,750 2025 Senior Notes 352,016 204,758 494,985 382,708 The carrying value on the balance sheet of the Revolving Credit Facility is its fair value due to their floating interest rates. The fair value for the 2022 and 2025 Senior Notes is based on an average of nonbinding broker quotes. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the 2022 and 2025 Senior Notes.

PARTNERS' CAPITAL AND MEZZANINE

PARTNERS' CAPITAL AND MEZZANINE CAPITAL	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
PARTNERS' CAPITAL AND MEZZANINE CAPITAL	10. PARTNERS' CAPITAL AND MEZZANINE CAPITAL A rollforward of the number of common units follows. Common Units Units, December 31, 2019 (1) 45,318,866 Net units issued under the SMLP LTIP 1,028,654 Impact of GP Buy-In Transaction (1,990,303 ) Preferred Unit Exchange 12,267,670 Units, September 30, 2020 (1) 56,624,887 (1) following the closing of the GP Buy-In transaction GP Buy-In Transaction. The purchase price for the SMLP common units reflected in the unaudited condensed consolidated statement of partners’ capital for the nine months ended September 30, 2020 is comprised of the (i) the $35.0 million cash payment to ECP, (ii) the $2.3 million fair value for the issuance of 10,000,000 warrants, and (iii) $6.8 million of advisory fees and other direct costs related to closing the GP Buy-In Transaction. Series A Preferred Units. In 2017, the Partnership issued 300,000 Series A Preferred Units representing limited partner interests in the Partnership at a price to the public of $1,000 per unit as described in the 2019 Annual Report. In connection with the GP Buy-In Transaction, the Partnership suspended its distributions to holders of its Series A Preferred Units, commencing with respect to the quarter ending March 31, 2020. On June 18, 2020, the Partnership, commenced an offer to exchange any and all of its Series A Preferred Units for newly issued SMLP common units (the “Exchange Offer”). On July 28, 2020, the Exchange Offer expired and the Partnership exchanged 62,816 Series A Preferred Units for 12,267,670 SMLP common units, net of units withheld for tax withholdings. As of September 30, 2020, the Partnership had 237,184 Series A Preferred Units outstanding. Subsidiary Series A Preferred Units. The Partnership issued 53,784 Subsidiary Series A Preferred Units during the nine months ended September 30, 2020 at a price of $1,000 per unit and has cumulatively issued 83,842 Subsidiary Series A Preferred Units since the instrument’s initial issuance in December 2019. Net proceeds received during the nine months ended September 30, 2020 totaled $48.7 million (after deducting underwriting discounts and offering expenses) and were used to fund the Partnership’s share of capital expenditures associated with the Double E Project. The proceeds associated with the issuance of Subsidiary Series A Preferred Units are restricted for funding the Double E Project and are classified as restricted cash in the accompanying unaudited condensed consolidated balance sheets The Partnership records its Subsidiary Series A Preferred Units at fair value upon issuance, net of issuance costs, and subsequently records an effective interest method accretion amount each reporting period to accrete the carrying value to a most probable redemption value that is based on a predetermined internal rate of return measure. The Partnership also elected to make payment- in-kind (“PIK”) distributions to holders of the Subsidiary Series A Preferred Unit s during the nine months ended September 30, 2020 and these PIK distributions increase the liquidation preference on each Subsidiary Series A Preferred Unit. Ultimately, Net Income (Loss) Attributable to common limited partners includes adjustments for PIK distributions and redemption accretion. If the Subsidiary Series A Preferred Units were redeemed on September 30, 2020, the redemption amount would be $104.8 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 December 31, 2019 to September 30, 2020: September 30, 2020 (in thousands) Balance at December 31, 2019 $ 27,450 New issuances 50,000 PIK distributions 3,784 Issuance costs (1,290 ) Redemption accretion 5,856 Balance at September 30, 2020 (1) $ 85,800 (1) Warrants. On May 28, 2020 and in connection with the GP Buy-In Transaction, the Partnership issued (i) a warrant to purchase up to 8,059,609 SMLP common units to ECP NewCo (the “ECP NewCo Warrant”) and (ii) a warrant to purchase up to 1,940,391 SMLP common units to ECP Holdings (the “ECP Holdings Warrant” and together with the ECP NewCo Warrant, the “ECP Warrants”). The exercise price under the ECP Warrants is $1.023 per SMLP common unit and the Partnership may issue a maximum of 10,000,000 SMLP common units under the ECP Warrants. Upon exercise of the ECP Warrants, each of ECP NewCo and ECP Holdings may receive, at its election: (i) a number of SMLP common units equal to the number of SMLP common units for which the ECP Warrants are being exercised, if exercising the ECP Warrants by cash payment of the exercise price; (ii) a number of SMLP common units equal to the product of the number of common units being exercised multiplied by (a) the difference between the average of the daily volume-weighted average price (“VWAP”) of the SMLP common units on the New York Stock Exchange (the “NYSE”) on each of the three trading days prior to the delivery of the notice of exercise (the “VWAP Average”) and the exercise price (the “VWAP Difference”), divided by (b) the VWAP Average; and/or (iii) an amount in cash, to the extent that the Partnership’s leverage ratio would be at least 0.5x less than the maximum applicable ratio set forth in the Revolving Credit Facility, equal to the product of (a) the number of SMLP common units exercised and (b) the VWAP Difference, subject to certain adjustments under the ECP Warrants. The ECP Warrants are subject to standard anti-dilution adjustments for stock dividends, stock splits (including reverse splits) and recapitalizations and are exercisable at any time on or before May 28, 2023. Upon exercise of the ECP Warrants, the proceeds to the holders of the ECP Warrants, whether in the form of cash or common units, will be capped at $2.00 per SMLP common unit above the exercise price. At issuance the ECP Warrants were valued at $2.3 million using a Black-Scholes model and accounted for as a liability instrument. At September 30, 2020, the ECP Warrants were valued at $1.5 million. SMLP General Partner and Incentive Distribution Rights (“IDR”) Exchange. In March 2019, and prior to the GP Buy-In Transaction, a subsidiary of Summit Investments cancelled its IDR agreement with SMLP and converted its 2% economic general partner interest to a non-economic general partner interest in exchange for 8,750,000 SMLP common units. This exchange is reflected in the Consolidated Statements of Partners’ Capital as a reduction to noncontrolling interest and an increase to Partners’ Capital. Cash Distributions Paid and Declared. Prior to the GP Buy-In Transaction, SMLP paid the following per-unit distributions during the three and nine month periods ended September 30 (all payments represent per-unit distributions based on the SMLP common units outstanding prior to the GP Buy-In Transaction): Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 Per-unit distributions to unitholders $ — $ 0.2875 $ 0.125 $ 1.1500 In connection with the GP Buy-In Transaction, With respect to our Subsidiary Series A Preferred Units relating to the three and nine months ended September 30, 2020, the Partnership declared a PIK of the quarterly distribution, which resulted in the issuance of 45 Subsidiary Series A Preferred Units and 1,442 Subsidiary Series A Preferred Units, respectively. This PIK amount equates to a distribution of $32.1133 and $17.5099 per Subsidiary Series A Preferred Unit for the three and nine months ended September 30, 2020, respectively, or $70 on an annualized basis. In addition, the Partnership issued approximately 38 Subsidiary Series A Preferred Units related to the remaining undrawn commitment (as defined in the underlying agreement with TPG Energy Solutions Anthem, L.P.) as of and for the nine months ended September 30, 2020.

EARNINGS PER UNIT

EARNINGS PER UNIT	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 2020 2019 (In thousands, except per-unit amounts) Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) attributable to limited partners $ 25,629 $ (789 ) $ 89,386 $ (11,130 ) Less: Net income attributable to Series A Preferred Units 6,481 7,125 20,731 21,375 Net income attributable to Subsidiary Series A Preferred Units 7,298 — 9,640 — Add: Deemed capital contribution from Series A Preferred Unit Exchange Offer 54,945 — 54,945 — Net income (loss) attributable to common limited partners $ 66,795 $ (7,914 ) $ 113,960 $ (32,505 ) Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic (1) 51,974 45,319 47,331 45,319 Effect of nonvested phantom units 1,676 — 1,451 — Weighted-average common units outstanding – diluted 53,650 45,319 48,782 45,319 Net Income (Loss) per limited partner unit: Common unit – basic $ 1.29 $ (0.17 ) $ 2.41 $ (0.72 ) Common unit – diluted $ 1.25 $ (0.17 ) $ 2.34 $ (0.72 ) Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 4,031 176 3,353 70 (1 ) As discussed in Note 8 - Debt, the SMPH Term Loan is secured by 34.6 million SMLP common units owned by SMP Holdings. These common units are not included in the calculation of EPU because they are not deemed contingently issuable under GAAP. Upon closing the TL Restructuring, the 34.6 million SMLP common units pledged under the SMPH Term Loan will be considered outstanding and included in the calculation of EPU.

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Elements [Abstract]
SUPPLEMENTAL CASH FLOW INFORMATION	12. SUPPLEMENTAL CASH FLOW INFORMATION Nine months ended September 30, 2020 2019 (In thousands) Supplemental cash flow information: Cash interest paid $ 62,441 $ 66,435 Less capitalized interest 2,268 5,752 Interest paid (net of capitalized interest) $ 60,173 $ 60,683 Cash paid for taxes $ — $ 150 Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 10,233 $ 22,166 Warrant issuance for GP Buy-In Transaction 2,300 — Asset contribution to an equity method investment — 23,643 Right-of-use assets relating to ASC Topic 842 2,964 5,448 Accretion of Subsidiary Series A Preferred Units 5,856 —

UNIT-BASED AND NONCASH COMPENSA

UNIT-BASED AND NONCASH COMPENSATION	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
UNIT-BASED AND NONCASH COMPENSATION	13. UNIT-BASED AND NONCASH COMPENSATION SMLP Long-Term Incentive Plan. The SMLP LTIP provides for equity awards to eligible officers, employees, consultants and directors. Items to note: • In March 2020, the Partnership granted 3,811,301 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 $0.55 and vest ratably over a three-year • In March 2020, the Partnership issued 549,450 common units to the Partnership’s three independent directors in connection with their annual compensation plan. • In June 2020, the Partnership issued 187,500 common units to three new independent directors in connection with their annual compensation plan. • During the nine months ended September 30, 2020, 0.8 million phantom units vested. • In March 2020, the Partnership increased the number of common units authorized under the SMLP LTIP to 15,000,000 common units and extended the term of the SMLP LTIP for 10 years. • As of September 30, 2020, approximately 6.3 common units remained available for future issuance under the SMLP LTIP.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2020
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 by the Partnership in the future. The Partnership is 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. The incident, which was covered by insurance policies, was subject to maximum coverage of $ 25.0 million from its pollution liability insurance policy and $ 200.0 million from its property and business interruption insurance policy. The pollution liability policy was exhausted in 2015. A rollforward of the Partnership’s undiscounted accrued environmental remediation liabilities follows. Total (In thousands) Accrued environmental remediation, January 1, 2020 $ 4,651 Payments made (1,095 ) Accrued environmental remediation, September 30, 2020 $ 3,556 As of September 30, 2020, the Partnership has recognized (i) a current liability for remediation effort expenditures expected to be incurred within the next 12 months and (ii) a noncurrent liability for estimated remediation expenditures expected to be incurred subsequent to September 30, 2021. Each of these amounts represent our best estimate for costs expected to be incurred. Neither of these amounts have been discounted to its present value. Prior to the GP Buy-In Transaction, Summit Investments and SMP Holdings indemnified the Partnership for certain obligations and liabilities related to the incident. As a result of the GP Buy-In Transaction, the Partnership continues to be indemnified by Summit Investments and SMP Holdings, both subsidiaries of the Partnership, but is no longer indemnified for these obligations by a third party that is not a subsidiary of the Partnership. The U.S. Department of Justice issued grand jury subpoenas to the Partnership requesting certain materials related to the Meadowlark Midstream rupture. Based on information currently available to the Partnership, the Partnership believes a loss for claims and/or actions arising from the Meadowlark Midstream rupture is probable. Due to the complexity surrounding the resolution of the Meadowlark Midstream rupture, the Partnership is not able to reasonably estimate the extent of the Partnership’s loss for this matter, or to express an opinion regarding the ultimate outcome. Any such loss, if incurred, could be material. Legal Proceedings. The Partnership is involved in various litigation and administrative proceedings arising in the normal course of business. In the opinion of management, any liabilities that may result from these claims or those arising in the normal course of business would not individually or in the aggregate have a material adverse effect on the Partnership's financial position or results of operations.

DISPOSITIONS AND RESTRUCTURING

DISPOSITIONS AND RESTRUCTURING	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
DISPOSITIONS AND RESTRUCTURING	15. DISPOSITIONS AND RESTRUCTURING Tioga Midstream Disposition. In February 2019, the Partnership entered into two Purchase and Sale Agreements (the “Tioga PSAs”) with Hess Infrastructure Partners LP and Hess North Dakota Pipelines LLC (collectively, “Hess Infrastructure”), pursuant to which the Partnership agreed to sell the Tioga Midstream system to Hess Infrastructure for a combined cash purchase price of $90 million, subject to adjustments as provided in the Tioga PSAs (the “Tioga Midstream Sale”). On March 22, 2019, the Partnership closed the Tioga Midstream Sale and recorded a gain on sale of $0.9 million based on the difference between the consideration received and the carrying value for Tioga Midstream at closing. The gain is included in the Gain on asset sales, net caption on the unaudited condensed consolidated statement of operations. The financial results of Tioga Midstream (a component of the Williston Basin reportable segment) are included in the Partnership’s unaudited condensed consolidated financial statements and footnotes for the period from January 1, 2019 through March 22, 2019. Restructuring Activities. As of December 31, 2019, the Partnership had $3.3 million of unpaid employee severance costs related to 2019 restructuring initiatives that resulted in certain management, facility and organizational changes. During the three and nine month periods ended September 30, 2020, the Partnership’s 2019 restructuring initiatives resulted in additional restructuring costs of $0.1 million and $3.4 million, respectively. The Partnership paid out $6.4 million of these 2019 restructuring costs during the nine months ended September 30, 2020 and has a $0.3 million current liability for unpaid employee severance costs at September 30, 2020 related to these 2019 restructuring initiatives. The 2019 restructuring activities primarily consisted of employee-related costs and consulting costs in support of the restructuring initiatives. Restructuring costs are included within the general and administrative expense caption on the condensed consolidated statement of operations.

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
SEGMENT INFORMATION	16. SEGMENT INFORMATION As of September 30, 2020, 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, Bison Midstream and Meadowlark Midstream; • the DJ Basin, which is served by Niobrara G&P; • the Permian Basin, which is served by Summit Permian; • the Piceance Basin, which is served by Grand River; • the Barnett Shale, which is served by DFW Midstream; and • the Marcellus Shale, which is served by Mountaineer Midstream. Until March 22, 2019, the Partnership owned Tioga Midstream, a crude oil, produced water and associated natural gas gathering system operating in the Williston Basin. Refer to Note 15 – Dispositions and Restructuring to the unaudited condensed consolidated financial statements for details on the sale of Tioga Midstream. Each of the Partnership’s reportable segments provide midstream services in a specific geographic area and 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. For the three and nine months ended September 30, 2020, other than the investment activity described in Note 6 – 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 are: (i) not specifically attributable to a reportable segment; (ii) not individually reportable (such as Double E); or (iii) that have not been allocated to the Partnership’s reportable segments for the purpose of evaluating their performance, including certain general and administrative expense items, certain natural gas and crude oil marketing services, construction management fees related to the Double E Project and transaction costs. Assets by reportable segment follow. September 30, 2020 December 31, 2019 (In thousands) Assets (1) Utica Shale $ 208,090 $ 206,368 Ohio Gathering 263,639 275,000 Williston Basin 443,506 452,152 DJ Basin 204,206 205,308 Permian Basin 167,707 185,708 Piceance Basin 596,148 631,140 Barnett Shale 349,254 350,638 Marcellus Shale 182,900 184,631 Total reportable segment assets 2,415,450 2,490,945 Corporate and Other 158,029 83,153 Total assets $ 2,573,479 $ 2,574,098 (1) Segment adjusted EBITDA by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 7,453 $ 7,864 $ 24,074 $ 20,697 Ohio Gathering 7,129 10,435 22,582 29,584 Williston Basin 11,713 13,840 40,632 49,224 DJ Basin 4,766 6,554 15,016 12,043 Permian Basin 893 210 4,302 (996 ) Piceance Basin 21,503 24,044 66,794 74,627 Barnett Shale 7,205 10,901 24,475 33,483 Marcellus Shale 6,022 4,958 16,230 14,735 Total of reportable segments' measures of profit $ 66,684 $ 78,806 $ 214,105 $ 233,397 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, 2020 2019 2020 2019 (In thousands) Reconciliation of income (loss) before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit: Income (loss) before income taxes and income (loss) from equity method investees $ 25,132 $ (10,431 ) $ 78,862 $ (45,757 ) Add: Corporate and Other expense 6,874 7,119 28,484 32,024 Interest expense 19,018 23,462 64,836 68,547 Gain on early extinguishment of debt (24,690 ) — (78,925 ) — Depreciation and amortization (1) 29,739 27,677 89,505 83,030 Proportional adjusted EBITDA for equity method investees 7,129 10,435 22,582 29,584 Adjustments related to MVC shortfall payments 2,292 3,534 (859 ) 2,868 Adjustments related to capital reimbursement activity (328 ) (145 ) (776 ) (1,906 ) Unit-based and noncash compensation 1,622 1,291 6,191 5,370 Gain on asset sales, net (104 ) (347 ) (270 ) (1,595 ) Long-lived asset impairment — — 4,475 45,021 Goodwill impairment — 16,211 — 16,211 Total of reportable segments' measures of profit $ 66,684 $ 78,806 $ 214,105 $ 233,397 (1)

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	17. SUBSEQUENT EVENTS Open Market Repurchases of 2025 Senior Notes. In October 2020, the Partnership repurchased an additional $95.6 million of the outstanding 2025 Senior Notes for total cash consideration of $64.8 million TL Restructuring. In October 2020, the Partnership obtained consents for the TL Restructuring from 100% of the Term Loan Lenders and subsequently filed a Form S-1 registration statement with the Securities and Exchange Commission on November 3, 2020 to register the 34.6 million SMLP common units to be issued to the lenders of the SMPH Term Loan upon consummation of the TL Restructuring. Once the Form S-1 registration statement becomes effective and administrative procedures are performed, the Partnership will close the TL Restructuring and recognize a gain on early debt extinguishment. Reverse Unit Split. On October 15, 2020, the Board of Directors of the General Partner authorized a reverse unit split (the “Reverse Unit Split”) of the Partnership’s common units. The exchange ratio of the Reverse Unit Split is 1-for-15 FERC Approval. In October 2020, Double E received Federal Energy Regulatory Commission ("FERC") approval of its application to construct and operate the Double E Pipeline Project, pursuant to Section 7(c) of the Natural Gas Act. Upon fulfilling certain remaining requirements, including finalizing a right-of-way grant from the Bureau of Land Management and filing an implementation plan with the FERC, Double E expects to receive FERC's notice to proceed with construction.

SUMMARY OF RECENTLY ISSUED AC_2

SUMMARY OF RECENTLY ISSUED ACCOUNTING STANDARDS APPLICABLE TO THE PARTNERSHIP (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. The Partnership reviews new pronouncements to determine the impact, if any, on its financial statements. Accounting standards that have or could possibly have a material effect on the Partnership’s financial statements are discussed below. Recently Adopted Accounting Pronouncements . The Partnership recently adopted the following accounting pronouncements: • 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 condensed 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 condensed consolidated financial statements or disclosures. Accounting Pronouncements Not Yet Adopted . The Partnership has not yet adopted the following accounting pronouncements as of September 30, 2020: • ASU No. 2020-06 Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815 – 40) (“ASU 2020-06”). ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. The ASU is part of the FASB’s simplification initiative, which aims to reduce unnecessary complexity in U.S. GAAP. The ASU’s amendments are effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years. The Partnership is currently evaluating the provisions of ASU 2020-06 to determine its impact on the Partnership’s condensed consolidated financial statements and disclosures. • ASU No. 2020-04 Reference Rate Reform (“ASU 2020-04”). ASU 2020-04 provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform on financial reporting. The amendments in ASU 2020-04 are effective as of March 12, 2020 through December 31, 2022. The Partnership is currently evaluating the provisions of ASU 2020-04 to determine its impact on the Partnership’s condensed consolidated financial statements and disclosures.
Basis of Presentation	Presentation and Consolidation. The condensed consolidated financial statements contained in this report include all normal and recurring material adjustments that, in the opinion of management, are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented herein. The accompanying condensed consolidated financial statements were prepared using GAAP for interim financial information and in accordance with the rules and regulations of the Securities and Exchange Commission. As permitted under those rules, certain information relating to the Partnership’s organization and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been appropriately condensed or omitted. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and the notes thereto included in the Partnership ’s Annual Report for the year ended December 31, 2019 (“2019 Annual Report”). The Partnership believes the disclosures made are adequate to make the information presented not misleading . Risks and Uncertainties. The Partnership is closely monitoring the impact of the outbreak of COVID-19 on all aspects of its business, including how it has impacted and will impact its customers, employees, supply chain and distribution network. While COVID-19 did not have a material adverse effect on the Partnership’s reported results for the first nine months of 2020, the Partnership is unable to predict the ultimate impact that COVID-19 may have on its business, future results of operations, financial position or cash flows. Given the dynamic nature of the COVID-19 pandemic and related market conditions, the Partnership cannot reasonably estimate the period of time that these events will persist or the full extent of the impact they will have on its business. The full extent to which the Partnership’s operations may be impacted by the COVID-19 pandemic will depend largely on future developments, which are highly uncertain and cannot be accurately predicted, including changes in the severity of the pandemic, countermeasures taken by governments, businesses and individuals to slow the spread of the pandemic, and the ability of pharmaceutical companies to develop effective and safe vaccines and therapeutic drugs. Furthermore, the impacts of a potential worsening of global economic conditions and the continued disruptions to and volatility in the financial markets remain unknown.

REVENUE (Tables)

REVENUE (Tables)	9 Months Ended
	Sep. 30, 2020
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 2020 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments. 2020 2021 2022 2023 2024 Thereafter (In thousands) Gathering services and related fees $ 29,678 $ 102,127 $ 84,736 $ 66,693 $ 50,608 $ 56,912
Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments	Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 16 – Segment Information. 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 All other segments — — 644 644 Total $ 71,964 $ 10,783 $ 7,406 $ 90,153 Three months ended September 30, 2019 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 8,865 $ - $ - $ 8,865 Williston Basin 16,685 1,878 2,555 21,118 DJ Basin 7,039 93 735 7,867 Permian Basin 986 3,797 102 4,885 Piceance Basin 30,120 1,733 1,258 33,111 Barnett Shale 11,286 4,828 1,706 17,820 Marcellus Shale 5,987 — — 5,987 Total reportable segments 80,968 12,329 6,356 99,653 All other segments — (110 ) 644 534 Total $ 80,968 $ 12,219 $ 7,000 $ 100,187 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 All other segments — — 1,931 1,931 Total $ 229,667 $ 35,246 $ 22,150 $ 287,063 Nine months ended September 30, 2019 Gathering services and related fees Natural gas, NGLs and condensate sales Other revenues Total (in thousands) Reportable Segments: Utica Shale $ 23,951 $ - $ - $ 23,951 Williston Basin 58,076 11,231 8,133 77,440 DJ Basin 14,784 279 2,776 17,839 Permian Basin 1,938 10,424 183 12,545 Piceance Basin 92,515 6,139 3,341 101,995 Barnett Shale 35,739 11,705 5,008 52,452 Marcellus Shale 18,081 — — 18,081 Total reportable segments 245,084 39,778 19,441 304,303 All other segments (2,045 ) 28,660 363 26,978 Total $ 243,039 $ 68,438 $ 19,804 $ 331,281
Schedule of Information about Contract Assets from Contracts with Customers	The following table provides information about contract assets from contracts with customers: September 30, 2020 (In thousands) Contract assets, January 1, 2020 $ 3,902 Additions 16,442 Transfers out (2,275 ) Contract assets, September 30, 2020 $ 18,069

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Schedule of property, plant, and equipment, net	Details on property, plant and equipment follow. September 30, 2020 December 31, 2019 (In thousands) Gathering and processing systems and related equipment $ 2,197,087 $ 2,182,950 Construction in progress 78,146 78,716 Land and line fill 10,440 10,137 Other 60,589 54,595 Total 2,346,262 2,326,398 Less accumulated depreciation (505,978) (443,909) Property, plant and equipment, net $ 1,840,284 $ 1,882,489
Schedule of depreciation expense and capitalized interest costs	Depreciation expense and capitalized interest follow. Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (In thousands) Depreciation expense $ 21,537 $ 19,474 $ 64,899 $ 58,160 Capitalized interest 1,449 1,391 2,268 5,752

EQUITY METHOD INVESTMENTS (Tabl

EQUITY METHOD INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
Equity Method Investments And Joint Ventures [Abstract]
Equity Method Investments	As of September 30, 2020 and December 31, 2019, the Partnership’s ownership interest in Ohio Gathering was 38.2% and 38.5%, respectively, and provided below is the September 30, 2020 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 (in thousands). Investment in Ohio Gathering, September 30, 2020 $ 263,639 September cash distributions 3,870 Basis difference 218,757 Investment in Ohio Gathering (Books and records), August 31, 2020 $ 486,266

DEFERRED REVENUE (Tables)

DEFERRED REVENUE (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Rollforward of deferred revenue	A rollforward of current deferred revenue follows. Total (In thousands) Current deferred revenue, January 1, 2020 $ 13,493 Additions 15,433 Less: revenue recognized (11,099) Current deferred revenue, September 30, 2020 $ 17,827 A rollforward of noncurrent deferred revenue follows. Total (In thousands) Noncurrent deferred revenue, January 1, 2020 $ 38,709 Additions 18,402 Less: reclassification to current deferred revenue (15,356) Noncurrent deferred revenue, September 30, 2020 $ 41,755

DEBT (Tables)

DEBT (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of debt and capital leases	Debt consisted of the following: September 30, 2020 December 31, 2019 (In thousands) Revolving Credit Facility : Summit Holdings' variable rate senior secured Revolving Credit Facility (2.90% at September 30, 2020 and 4.55% at December 31, 2019) due May 2022 $ 808,500 $ 677,000 ECP Loans : Summit Holdings' 8.00% senior secured term loans due March 2021 — — 2022 Senior Notes : Summit Holdings' 5.5% senior unsecured notes due August 2022 234,047 300,000 Less: unamortized debt issuance costs (1) (997 ) (1,686 ) 2025 Senior Notes : Summit Holdings' 5.75% senior unsecured notes due April 2025 355,071 500,000 Less: unamortized debt issuance costs (1) (3,055 ) (5,015 ) SMPH Term Loan : SMP Holdings' variable rate senior secured term loan (7.00% at September 30, 2020 and 7.80% at December 31, 2019) due May 2022 155,200 161,500 Less: unamortized debt issuance costs (1) (2,724 ) (3,974 ) Total debt 1,546,042 1,627,825 Less: current portion (155,200) (5,546) Total long-term debt $ 1,390,842 $ 1,622,279 (1)
Schedule of extinguishment of debt	ECP Loan Repayment Open Market Repurchases Tender Offers Total 2022 2025 2022 2025 Senior Notes Senior Notes Senior Notes Senior Notes (in thousands) 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, 2020
Fair Value Disclosures [Abstract]
Summary of the estimated fair value of debt instruments	A summary of the estimated fair value of our debt financial instruments follows. September 30, 2020 December 31, 2019 Carrying Value, Net Estimated fair value (Level 2) Carrying Value, Net Estimated fair value (Level 2) (In thousands) 2022 Senior Notes $ 233,050 $ 169,684 $ 298,314 $ 266,750 2025 Senior Notes 352,016 204,758 494,985 382,708

PARTNERS' CAPITAL AND MEZZANI_2

PARTNERS' CAPITAL AND MEZZANINE CAPITAL (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of partner units activity	A rollforward of the number of common units follows. Common Units Units, December 31, 2019 (1) 45,318,866 Net units issued under the SMLP LTIP 1,028,654 Impact of GP Buy-In Transaction (1,990,303 ) Preferred Unit Exchange 12,267,670 Units, September 30, 2020 (1) 56,624,887 (1) following the closing of the GP Buy-In transaction
Change in subsidiary	The following table shows the change in our Subsidiary Series A Preferred Unit balance from December 31, 2019 to September 30, 2020: September 30, 2020 (in thousands) Balance at December 31, 2019 $ 27,450 New issuances 50,000 PIK distributions 3,784 Issuance costs (1,290 ) Redemption accretion 5,856 Balance at September 30, 2020 (1) $ 85,800 (1)
Details of cash distributions	Prior to the GP Buy-In Transaction, SMLP paid the following per-unit distributions during the three and nine month periods ended September 30 (all payments represent per-unit distributions based on the SMLP common units outstanding prior to the GP Buy-In Transaction): Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 Per-unit distributions to unitholders $ — $ 0.2875 $ 0.125 $ 1.1500

EARNINGS PER UNIT (Tables)

EARNINGS PER UNIT (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of earnings per limited partner unit	The following table details the components of EPU. Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (In thousands, except per-unit amounts) Numerator for basic and diluted EPU: Allocation of net income (loss) among limited partner interests: Net income (loss) attributable to limited partners $ 25,629 $ (789 ) $ 89,386 $ (11,130 ) Less: Net income attributable to Series A Preferred Units 6,481 7,125 20,731 21,375 Net income attributable to Subsidiary Series A Preferred Units 7,298 — 9,640 — Add: Deemed capital contribution from Series A Preferred Unit Exchange Offer 54,945 — 54,945 — Net income (loss) attributable to common limited partners $ 66,795 $ (7,914 ) $ 113,960 $ (32,505 ) Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic (1) 51,974 45,319 47,331 45,319 Effect of nonvested phantom units 1,676 — 1,451 — Weighted-average common units outstanding – diluted 53,650 45,319 48,782 45,319 Net Income (Loss) per limited partner unit: Common unit – basic $ 1.29 $ (0.17 ) $ 2.41 $ (0.72 ) Common unit – diluted $ 1.25 $ (0.17 ) $ 2.34 $ (0.72 ) Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 4,031 176 3,353 70 (1 )

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Schedule of supplemental cash flow information	Nine months ended September 30, 2020 2019 (In thousands) Supplemental cash flow information: Cash interest paid $ 62,441 $ 66,435 Less capitalized interest 2,268 5,752 Interest paid (net of capitalized interest) $ 60,173 $ 60,683 Cash paid for taxes $ — $ 150 Noncash investing and financing activities: Capital expenditures in trade accounts payable (period-end accruals) $ 10,233 $ 22,166 Warrant issuance for GP Buy-In Transaction 2,300 — Asset contribution to an equity method investment — 23,643 Right-of-use assets relating to ASC Topic 842 2,964 5,448 Accretion of Subsidiary Series A Preferred Units 5,856 —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of accrued environmental remediation	A rollforward of the Partnership’s undiscounted accrued environmental remediation liabilities follows. Total (In thousands) Accrued environmental remediation, January 1, 2020 $ 4,651 Payments made (1,095 ) Accrued environmental remediation, September 30, 2020 $ 3,556

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of assets by reportable segment	Assets by reportable segment follow. September 30, 2020 December 31, 2019 (In thousands) Assets (1) Utica Shale $ 208,090 $ 206,368 Ohio Gathering 263,639 275,000 Williston Basin 443,506 452,152 DJ Basin 204,206 205,308 Permian Basin 167,707 185,708 Piceance Basin 596,148 631,140 Barnett Shale 349,254 350,638 Marcellus Shale 182,900 184,631 Total reportable segment assets 2,415,450 2,490,945 Corporate and Other 158,029 83,153 Total assets $ 2,573,479 $ 2,574,098 (1)
Reconciliation of net income to adjusted EBITDA	Segment adjusted EBITDA by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 7,453 $ 7,864 $ 24,074 $ 20,697 Ohio Gathering 7,129 10,435 22,582 29,584 Williston Basin 11,713 13,840 40,632 49,224 DJ Basin 4,766 6,554 15,016 12,043 Permian Basin 893 210 4,302 (996 ) Piceance Basin 21,503 24,044 66,794 74,627 Barnett Shale 7,205 10,901 24,475 33,483 Marcellus Shale 6,022 4,958 16,230 14,735 Total of reportable segments' measures of profit $ 66,684 $ 78,806 $ 214,105 $ 233,397 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, 2020 2019 2020 2019 (In thousands) Reconciliation of income (loss) before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit: Income (loss) before income taxes and income (loss) from equity method investees $ 25,132 $ (10,431 ) $ 78,862 $ (45,757 ) Add: Corporate and Other expense 6,874 7,119 28,484 32,024 Interest expense 19,018 23,462 64,836 68,547 Gain on early extinguishment of debt (24,690 ) — (78,925 ) — Depreciation and amortization (1) 29,739 27,677 89,505 83,030 Proportional adjusted EBITDA for equity method investees 7,129 10,435 22,582 29,584 Adjustments related to MVC shortfall payments 2,292 3,534 (859 ) 2,868 Adjustments related to capital reimbursement activity (328 ) (145 ) (776 ) (1,906 ) Unit-based and noncash compensation 1,622 1,291 6,191 5,370 Gain on asset sales, net (104 ) (347 ) (270 ) (1,595 ) Long-lived asset impairment — — 4,475 45,021 Goodwill impairment — 16,211 — 16,211 Total of reportable segments' measures of profit $ 66,684 $ 78,806 $ 214,105 $ 233,397 (1)

ORGANIZATION, BUSINESS OPERAT_2

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	May 28, 2020	Sep. 30, 2020	Dec. 31, 2019
Organization And Business Operations [Line Items]
Purchase agreement date		May 28, 2020
Common limited partner capital (shares)		56,624,887	45,318,866
Common Units
Organization And Business Operations [Line Items]
Number of common units purchased.	8,059,609
Common Units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (shares)		5,915,827
Summit Midstream Partners Holdings L L C
Organization And Business Operations [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan		34,604,581
SMLP common units not pledged as collateral under the SMPH Term Loan		10,714,285
Common units retire		16,630,112
Summit Investments
Organization And Business Operations [Line Items]
Cash paid to Acquire investment		$ 35
Summit Investments | Common Units
Organization And Business Operations [Line Items]
Number of common units purchased.		10,000,000

REVENUE - Schedule of Estimated

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) - Gathering Services and Related Fees $ in Thousands	Sep. 30, 2020USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-10-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	3 months
Revenue, remaining performance obligation	$ 29,678
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 102,127
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 84,736
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 66,693
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, remaining performance obligation	$ 50,608
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period
Revenue, remaining performance obligation	$ 56,912

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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 90,153	$ 100,187	$ 287,063	$ 331,281
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	644	534	1,931	26,978
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	89,509	99,653	285,132	304,303
Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	8,385	8,865	26,885	23,951
Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	19,035	21,118	68,612	77,440
Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	6,894	7,867	21,145	17,839
Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	7,566	4,885	21,635	12,545
Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	28,337	33,111	85,313	101,995
Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	12,421	17,820	42,508	52,452
Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,871	5,987	19,034	18,081
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues	71,964	80,968	229,667	243,039
Gathering Services and Related Fees | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	0	(2,045)
Gathering Services and Related Fees | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	71,964	80,968	229,667	245,084
Gathering Services and Related Fees | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	8,385	8,865	26,885	23,951
Gathering Services and Related Fees | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	10,941	16,685	47,145	58,076
Gathering Services and Related Fees | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	6,051	7,039	18,134	14,784
Gathering Services and Related Fees | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	2,595	986	7,617	1,938
Gathering Services and Related Fees | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	26,576	30,120	79,987	92,515
Gathering Services and Related Fees | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	10,545	11,286	30,865	35,739
Gathering Services and Related Fees | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	6,871	5,987	19,034	18,081
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues	10,783	12,219	35,246	68,438
Natural Gas, NGLs and Condensate Sales | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	0	(110)	0	28,660
Natural Gas, NGLs and Condensate Sales | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	10,783	12,329	35,246	39,778
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	4,958	1,878	12,413	11,231
Natural Gas, NGLs and Condensate Sales | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	17	93	158	279
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	4,803	3,797	13,537	10,424
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	528	1,733	1,932	6,139
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	477	4,828	7,206	11,705
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	0	0
Other Revenues
Disaggregation Of Revenue [Line Items]
Total revenues	7,406	7,000	22,150	19,804
Other Revenues | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	644	644	1,931	363
Other Revenues | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	6,762	6,356	20,219	19,441
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	3,136	2,555	9,054	8,133
Other Revenues | Reportable Segments | DJ Basin
Disaggregation Of Revenue [Line Items]
Total revenues	826	735	2,853	2,776
Other Revenues | Reportable Segments | Permian Basin
Disaggregation Of Revenue [Line Items]
Total revenues	168	102	481	183
Other Revenues | Reportable Segments | Piceance Basin
Disaggregation Of Revenue [Line Items]
Total revenues	1,233	1,258	3,394	3,341
Other Revenues | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	1,399	1,706	4,437	5,008
Other Revenues | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 0	$ 0

REVENUE - Schedule of Informati

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Contract With Customer Asset And Liability [Abstract]
Contract assets, beginning of period	$ 3,902
Additions	16,442
Transfers out	(2,275)
Contract assets, end of period	$ 18,069

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue From Contract With Customer [Line Items]
Receivables with customers	$ 53,800		$ 53,800		$ 90,400
Contract assets included in accounts receivable	18,069		18,069		$ 3,902
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 2,400	$ 2,400	$ 7,100	$ 7,800

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,346,262	$ 2,326,398
Less accumulated depreciation	(505,978)	(443,909)
Property, plant and equipment, net	1,840,284	1,882,489
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,197,087	2,182,950
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	78,146	78,716
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,440	10,137
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 60,589	$ 54,595

PROPERTY, PLANT, AND EQUIPMEN_4

PROPERTY, PLANT, AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Property, Plant and Equipment [Line Items]
Asset impairment charges			$ 10.2
Rights-of-way
Property, Plant and Equipment [Line Items]
Asset impairment charges			0.5
DJ Basin
Property, Plant and Equipment [Line Items]
Asset impairment charges	$ 34.7	$ 3.6
Barnett Shale | Fixed Assets
Property, Plant and Equipment [Line Items]
Asset impairment charges			$ 9.7

PROPERTY, PLANT, AND EQUIPMEN_5

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 21,537	$ 19,474	$ 64,899	$ 58,160
Capitalized interest	$ 1,449	$ 1,391	$ 2,268	$ 5,752

GOODWILL - Narrative (Details)

GOODWILL - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Line Items]
Goodwill impairment	$ 16,211	$ 0	$ 16,211
Mountaineer Midstream
Goodwill [Line Items]
Goodwill impairment	$ 16,200		$ 16,200

EQUITY METHOD INVESTMENTS - Nar

EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Additional cash investments	$ 12,400	$ 92,100
Double E
Schedule Of Equity Method Investments [Line Items]
Result of operations	$ 0	$ 0
OGC | Principal Owner
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest	38.20%	38.20%	38.50%

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, 2020	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, September 30, 2020	$ 389,088	$ 389,088
September cash distributions		19,859	$ 28,008
Investment in Ohio Gathering (Books and records), August 31, 2020		309,728
OGC | Summit Midstream Partners, LLC
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, September 30, 2020	263,639	$ 263,639
September cash distributions	3,870
Basis difference	218,757
Investment in Ohio Gathering (Books and records), August 31, 2020	$ 486,266

DEFERRED REVENUE - Rollforward

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 13,493
Current deferred revenue, Additions	15,433
Current deferred revenue, Less revenue recognized	(11,099)
Current deferred revenue, ending balance	17,827
Noncurrent deferred revenue, beginning balance	38,709
Noncurrent deferred revenue, Additions	18,402
Noncurrent deferred revenue, Less reclassification to current deferred revenue	(15,356)
Noncurrent deferred revenue, ending balance	$ 41,755

DEBT - Components of Long-Term

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Long-term debt		$ 1,390,842	$ 1,622,279
Summit Midstream Partners Holdings L L C
Line of Credit Facility [Line Items]
Total debt		1,546,042	1,627,825
Less: current portion		(155,200)	(5,546)
Long-term debt		1,390,842	1,622,279
Summit Midstream Partners Holdings L L C | Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility		808,500	677,000
Summit Midstream Partners Holdings L L C | Senior Secured Term Loan Due March 2021
Line of Credit Facility [Line Items]
Revolving credit facility		0	0
Summit Midstream Partners Holdings L L C | Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Unsecured notes		234,047	300,000
Less unamortized debt issuance costs	[1]	(997)	(1,686)
Summit Midstream Partners Holdings L L C | Senior Secured Term Loan Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility		155,200	161,500
Less unamortized debt issuance costs	[1]	(2,724)	(3,974)
Summit Midstream Partners Holdings L L C | Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Unsecured notes		355,071	500,000
Less unamortized debt issuance costs	[1]	$ (3,055)	$ (5,015)
[1]	Issuance costs are being amortized over the life of the SMPH Term Loan and the Senior Notes.

DEBT - Components of Long-Ter_2

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - Summit Midstream Partners Holdings L L C	Sep. 30, 2020	Dec. 31, 2019
Senior Secured Term Loan Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	7.00%	7.80%
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	2.90%	4.55%
Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Stated interest rate	5.75%	5.75%
Senior Secured Term Loan Due March 2021
Line of Credit Facility [Line Items]
Stated interest rate	8.00%	8.00%

DEBT - Revolving Credit Facilit

DEBT - Revolving Credit Facility (Narrative) (Details)	9 Months Ended
	Sep. 30, 2020USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, outstanding amount	$ 4,100,000
Current borrowing capacity	172,000,000
Debt defaults	0
Revolving credit facility
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,250,000,000
Revolving credit facility maturity date	2022-05
Accordion feature	$ 250,000,000
Commitment fee on unused portion of the facility	0.50%
Interest rate at period end	2.90%
Unused portion under the facility	$ 437,400,000
Revolving credit facility | LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.75%

DEBT - ECP Loans (Narrative) (D

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

DEBT - Term Loan (Narrative) (D

DEBT - Term Loan (Narrative) (Details) - Term Loan B [Member] - USD ($) $ in Millions	Apr. 17, 2020	Sep. 30, 2020	Sep. 30, 2020
Debt Instrument [Line Items]
Derivative, notional amount	$ 125
Derivative, beginning date	Apr. 30, 2020
Derivative, maturity date	Apr. 30, 2022
Unsettled gain		$ 0.1	$ 0.1
Debt issuance costs incurred			$ 0.2
LIBOR
Debt Instrument [Line Items]
Derivative, fixed interest rate	1.00%

DEBT - Liability Management Tra

DEBT - Liability Management Transactions (Narrative) (Details) - USD ($) $ in Thousands	Sep. 29, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Gains on extinguishment of debt		$ 24,690	$ 78,925	$ 0
Liability Management Transactions | Open Market Repurchases
Debt Instrument [Line Items]
Gains on extinguishment of debt			56,200
Liability Management Transactions | Tender Offers
Debt Instrument [Line Items]
Gains on extinguishment of debt			23,300
Liability Management Transactions | SMPH Term Loan Restructuring
Debt Instrument [Line Items]
Term Loan result in consensual debt discharge of full amount owed under Term Loan exchange	$ 155,200
Cash payments to creditors	26,500
Amount of common units pledged as collateral	34,600
Cash payment on the Deferred Purchase Price Obligation	$ 26,500
Liability Management Transactions | Senior Notes Due 2022 And 2025
Debt Instrument [Line Items]
Early extinguishment of debt		210,800	210,800
Liability Management Transactions | Senior Notes Due 2022 | Open Market Repurchases
Debt Instrument [Line Items]
Senior Notes repurchased		32,400	32,400
Cash consideration paid		82,900	82,900
Liability Management Transactions | Senior Notes Due 2022 | Tender Offers
Debt Instrument [Line Items]
Senior Notes repurchased		33,500	33,500
Cash consideration paid		48,700	48,700
Liability Management Transactions | Senior Notes Due April 2025 | Open Market Repurchases
Debt Instrument [Line Items]
Senior Notes repurchased		106,200	106,200
Cash consideration paid		82,900	82,900
Liability Management Transactions | Senior Notes Due April 2025 | Tender Offers
Debt Instrument [Line Items]
Senior Notes repurchased		38,700	38,700
Cash consideration paid		$ 48,700	$ 48,700

DEBT - Gain on Extinguishment o

DEBT - Gain on Extinguishment of Debt (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Gains on extinguishment of debt	$ 24,690	$ 78,925	$ 0
Liability Management Transactions | Open Market Repurchases and Tender Offer Repurchase
Debt Instrument [Line Items]
Gains on extinguishment of debt		$ 78,900

DEBT - Schedule of Extinguishme

DEBT - Schedule of Extinguishment of Debt (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Extinguishment Of Debt [Line Items]
Gain on repurchases of Senior Notes		$ 82,259
Debt issue costs		(1,945)
Transaction cost		(1,389)
Gain (loss) on extinguishment	$ 24,690	78,925	$ 0
ECP Loan Repayment
Extinguishment Of Debt [Line Items]
Debt issue costs		(361)
Transaction cost		(249)
Gain (loss) on extinguishment		(610)
Senior Notes Due 2022 | Open Market Repurchases
Extinguishment Of Debt [Line Items]
Gain on repurchases of Senior Notes		11,554
Debt issue costs		(143)
Transaction cost		(105)
Gain (loss) on extinguishment		11,306
Senior Notes Due 2022 | Tender Offers
Extinguishment Of Debt [Line Items]
Gain on repurchases of Senior Notes		9,223
Debt issue costs		(125)
Transaction cost		(465)
Gain (loss) on extinguishment		8,633
Senior Notes Due 2025 | Open Market Repurchases
Extinguishment Of Debt [Line Items]
Gain on repurchases of Senior Notes		46,003
Debt issue costs		(965)
Transaction cost		(105)
Gain (loss) on extinguishment		44,933
Senior Notes Due 2025 | Tender Offers
Extinguishment Of Debt [Line Items]
Gain on repurchases of Senior Notes		15,479
Debt issue costs		(351)
Transaction cost		(465)
Gain (loss) on extinguishment		$ 14,663

FINANCIAL INSTRUMENTS - Fair va

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
2022 Senior Notes | Carrying Value, Net
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 233,050	$ 298,314
2022 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	169,684	266,750
2025 Senior Notes | Carrying Value, Net
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	352,016	494,985
2025 Senior Notes | Fair Value | Estimated fair value (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 204,758	$ 382,708

PARTNERS' CAPITAL AND MEZZANI_3

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Schedule of Units (Details) - Common Units	9 Months Ended
	Sep. 30, 2020shares
Rollforwards of the number of partner units
Units, beginning balance (in shares)	45,318,866
Net units issued under the SMLP LTIP (in shares)	1,028,654
Impact of GP Buy-In Transaction	(1,990,303)
Preferred Unit Exchange	12,267,670
Units, ending balance (in shares)	56,624,887

PARTNERS' CAPITAL AND MEZZANI_4

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Partners' Capital and Schedule of Units (Parenthetical) (Details) - shares	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Partners Capital [Line Items]
Common limited partner capital (in shares), issued	56,624,887	45,318,866
Common Units
Partners Capital [Line Items]
Partners capital account units	56,600,000	45,300,000
Common limited partner capital (in shares), issued	1,000,000
Common Units | Preferred Unit Exchange
Partners Capital [Line Items]
Exchange Offer	12,300,000
Common Units | Term Loan B [Member]
Partners Capital [Line Items]
Common units pledged as collateral	34,600,000
Common units not pledged as collateral	10,700,000
Common Units | Energy Capital Partners
Partners Capital [Line Items]
Common units owned by ECP	5,900,000
Previously Reported | Common Units
Partners Capital [Line Items]
Partners capital account units	94,500,000

PARTNERS' CAPITAL AND MEZZANI_5

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 28, 2020	May 28, 2020	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Partners Capital [Line Items]
Preferred units issued				237,184	237,184		300,000
Common limited partner capital (in shares), outstanding				56,624,887	56,624,887		45,318,866
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued	62,816			53,784	53,784		83,842	300,000
Interest in partnership per unit				$ 1,000	$ 1,000			$ 1,000
Common limited partner capital (in shares), outstanding				237,184	237,184
Proceeds from issuance of common limited partners units					$ 48,700
Redemption amount				$ 104,800	$ 104,800
Series A Preferred Units | Paid-in-Kind Distributions
Partners Capital [Line Items]
Pro-rated issuance of preferred units				45	1,442
Pro-rated distribution of preferred units				$ 32.1133	$ 17.5099
Pro-rated distribution of preferred units						$ 70
Pro-rated issuance of preferred units related to undrawn commitment					38
Common Units
Partners Capital [Line Items]
Number of common units purchased.		8,059,609
General partner units converted	12,267,670
Exercise price of Warrants		$ 1.023
Valuation of warrants		$ 2,300		$ 1,500	$ 1,500
Warrant or right, reason for issuance, description					Upon exercise of the ECP Warrants, each of ECP NewCo and ECP Holdings may receive, at its election: (i) a number of SMLP common units equal to the number of SMLP common units for which the ECP Warrants are being exercised, if exercising the ECP Warrants by cash payment of the exercise price; (ii) a number of SMLP common units equal to the product of the number of common units being exercised multiplied by (a) the difference between the average of the daily volume-weighted average price (“VWAP”) of the SMLP common units on the New York Stock Exchange (the “NYSE”) on each of the three trading days prior to the delivery of the notice of exercise (the “VWAP Average”) and the exercise price (the “VWAP Difference”), divided by (b) the VWAP Average; and/or (iii) an amount in cash, to the extent that the Partnership’s leverage ratio would be at least 0.5x less than the maximum applicable ratio set forth in the Revolving Credit Facility, equal to the product of (a) the number of SMLP common units exercised and (b) the VWAP Difference, subject to certain adjustments under the ECP Warrants.
Common Units | Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner units converted			8,750,000
Common Units | ECP Holdings Warrant
Partners Capital [Line Items]
Number of common units purchased.		1,940,391
Common Units | Energy Capital Partners
Partners Capital [Line Items]
Warrants exercisable date		May 28, 2023
Common Units | Maximum
Partners Capital [Line Items]
Exercise price of Warrants		$ 2
Common units, issued		10,000,000
General Partner | Summit Midstream Partners, LP
Partners Capital [Line Items]
General partner interest			2.00%
General Partner | Common Units
Partners Capital [Line Items]
Cash paid to Acquire investment					$ 35,000
Number of common units purchased.					10,000,000
Advisory fees and other direct costs					$ 6,800
Fair value of warrants					$ 2,300

PARTNERS' CAPITAL AND MEZZANI_6

PARTNERS' CAPITAL AND MEZZANINE CAPITAL- Change in Subsidiary (Details)	9 Months Ended
	Sep. 30, 2020USD ($)shares
Partners Capital [Line Items]
Issuance costs	$ (3,900,000)
Series A Preferred Units
Partners Capital [Line Items]
Balance	$ 27,450,000
New issuances | shares	50,000
PIK distributions | shares	3,784
Issuance costs	$ (1,290,000)
Redemption accretion	5,856,000
Balance	$ 85,800,000	[1]
[1]	(1)

PARTNERS' CAPITAL AND MEZZANI_7

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Parenthetical (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Equity [Abstract]
Issuance costs	$ 3.9

PARTNERS' CAPITAL AND MEZZANI_8

PARTNERS' CAPITAL AND MEZZANINE CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.2875	$ 0.125	$ 1.1500

EARNINGS PER UNIT (Details)

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners		$ 25,629	$ (789)	$ 89,386	$ (11,130)
Deemed contribution on exchange of preferred units		$ 54,945		$ 54,945
Phantom Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		4,031	176	3,353	70
Limited Partner Interest Before Subordinated Units Converted To Common Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners		$ 25,629	$ (789)	$ 89,386	$ (11,130)
Series A Preferred Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners		6,481	7,125	20,731	21,375
Deemed contribution on exchange of preferred units		54,945		54,945
Series A Preferred Units | Subsidiaries
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners		7,298		9,640
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners		$ 66,795	$ (7,914)	$ 113,960	$ (32,505)
Basic (shares)	[1]	51,974,000	45,319,000	47,331,000	45,319,000
Effect of nonvested phantom units		1,676		1,451
Diluted (shares)		53,650,000	45,319,000	48,782,000	45,319,000
Common unit – basic		$ 1.29	$ (0.17)	$ 2.41	$ (0.72)
Common unit – diluted		$ 1.25	$ (0.17)	$ 2.34	$ (0.72)
[1]	As a result of the GP Buy-In Transaction, our historical results are those of Summit Investments. The number of common units of 45.3 million as of September 30, 2019 represents those of Summit Investments and has been used for the earnings per unit calculations presented herein.

EARNINGS PER UNIT (Parenthetica

EARNINGS PER UNIT (Parenthetical) (Details) - shares	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common limited partner capital (in shares), outstanding	56,624,887	45,318,866
Summit Midstream Partners Holdings L L C | Common Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common limited partner capital (in shares), outstanding			45,300,000

EARNINGS PER UNIT - Narrative (

EARNINGS PER UNIT - Narrative (Details) - Summit Midstream Partners Holdings L L C	Sep. 30, 2020shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan	34,604,581
Term Loan B [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan	34,600,000

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION - Schedule of supplemental cash flow information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental cash flow information:
Cash interest paid	$ 62,441	$ 66,435
Less capitalized interest	2,268	5,752
Interest paid (net of capitalized interest)	60,173	60,683
Cash paid for taxes		150
Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	10,233	22,166
Warrant issuance for GP Buy-In Transaction	2,300
Asset contribution to an equity method investment		23,643
ASC Topic 842
Noncash investing and financing activities:
Right-of-use assets relating to ASC Topic 842	2,964	$ 5,448
Series A Preferred Units
Noncash investing and financing activities:
Accretion of Subsidiary Series A Preferred Units	$ 5,856

UNIT-BASED AND NONCASH COMPEN_2

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) - SMLP LTIP	1 Months Ended		9 Months Ended
	Jun. 30, 2020Directorshares	Mar. 31, 2020Director$ / sharesshares	Sep. 30, 2020shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units remaining available			6,300,000
Phantom Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted units (in shares)		3,811,301
Grant date fair value (in dollars per share) | $ / shares		$ 0.55
Vesting period		3 years
Issued units (in shares)	187,500	549,450
No. of directors | Director	3	3
Units vested (in shares)			800,000
Number of authorized common units increased		15,000,000
Common units extended term		10 years

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - Maximum - Meadowlark Midstream Gathering System - Principal Owner	9 Months Ended
	Sep. 30, 2020USD ($)
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy	$ 25,000,000
Coverage from property and business interruption insurance policy	$ 200,000,000

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 4,651
Payments made	(1,095)
Accrued environmental remediation, ending balance	$ 3,556

DISPOSITIONS AND RESTRUCTURING

DISPOSITIONS AND RESTRUCTURING - Tioga Midstream Disposition (Details) - Partnership - Disposal, not discontinued operations $ in Millions	Mar. 22, 2019USD ($)	Feb. 28, 2019USD ($)Agreement
Business Acquisition [Line Items]
Number of purchase and sale agreements | Agreement		2
Cash purchase price of disposals		$ 90
Gain on sale of business	$ 0.9

DISPOSITIONS AND RESTRUCTURIN_2

DISPOSITIONS AND RESTRUCTURING - Restructuring Activities (Details) - Employee Related Costs - Partnership - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Severance costs			$ 3.3
Restructuring costs	$ 0.1	$ 3.4
Cash payment		6.4
Employee related cost included in other current liabilities	$ 0.3	$ 0.3

SEGMENT INFORMATION - Assets, R

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 2,573,479	$ 2,574,098
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,415,450	2,490,945
Reportable Segments | Utica Shale
Segment Reporting Information [Line Items]
Assets	208,090	206,368
Reportable Segments | Ohio Gathering
Segment Reporting Information [Line Items]
Assets	263,639	275,000
Reportable Segments | Williston Basin
Segment Reporting Information [Line Items]
Assets	443,506	452,152
Reportable Segments | DJ Basin
Segment Reporting Information [Line Items]
Assets	204,206	205,308
Reportable Segments | Permian Basin
Segment Reporting Information [Line Items]
Assets	167,707	185,708
Reportable Segments | Piceance Basin
Segment Reporting Information [Line Items]
Assets	596,148	631,140
Reportable Segments | Barnett Shale
Segment Reporting Information [Line Items]
Assets	349,254	350,638
Reportable Segments | Marcellus Shale
Segment Reporting Information [Line Items]
Assets	182,900	184,631
Corporate and Other
Segment Reporting Information [Line Items]
Assets	$ 158,029	$ 83,153

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Equity method investment	$ 389,088	$ 309,728
Corporate and Other | Double E
Segment Reporting Information [Line Items]
Capital expenditures	$ 125,400
Equity method investment		$ 34,700

SEGMENT INFORMATION - Adjusted

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 66,684	$ 78,806	$ 214,105	$ 233,397
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	7,453	7,864	24,074	20,697
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	7,129	10,435	22,582	29,584
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	11,713	13,840	40,632	49,224
DJ Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	4,766	6,554	15,016	12,043
Permian Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	893	210	4,302	(996)
Piceance Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	21,503	24,044	66,794	74,627
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	7,205	10,901	24,475	33,483
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 6,022	$ 4,958	$ 16,230	$ 14,735

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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting [Abstract]
Income (loss) before income taxes and equity method investment income (loss)	$ 25,132	$ (10,431)	$ 78,862	$ (45,757)
Add:
Corporate and Other expense	6,874	7,119	28,484	32,024
Interest expense	19,018	23,462	64,836	68,547
Gain on early extinguishment of debt	(24,690)		(78,925)	0
Depreciation and amortization	29,739	27,677	89,505	83,030
Proportional adjusted EBITDA for equity method investees	7,129	10,435	22,582	29,584
Adjustments related to MVC shortfall payments	2,292	3,534	(859)	2,868
Adjustments related to capital reimbursement activity	(328)	(145)	(776)	(1,906)
Unit-based and noncash compensation	1,622	1,291	6,191	5,370
Gain on asset sales, net	(104)	(347)	(270)	(1,595)
Long-lived asset impairment			4,475	45,021
Goodwill impairment		16,211	0	16,211
Total of reportable segments' measures of profit	$ 66,684	$ 78,806	$ 214,105	$ 233,397

SUBSEQUENT EVENTS - Narrative (

SUBSEQUENT EVENTS - Narrative (Details) $ / shares in Units, $ in Millions	Oct. 15, 2020$ / shares	Oct. 31, 2020USD ($)	Nov. 09, 2020shares	Nov. 03, 2020shares	Oct. 30, 2020shares	Sep. 30, 2020shares	Dec. 31, 2019shares
Subsequent Event [Line Items]
Common limited partner capital (in shares), outstanding						56,624,887	45,318,866
Subsequent Event | Summit Midstream GP, LLC | Reverse Unit Split
Subsequent Event [Line Items]
Reverse unit split ratio	0.06
Reverse unit split description	On October 15, 2020, the Board of Directors of the General Partner authorized a reverse unit split (the “Reverse Unit Split”) of the Partnership’s common units.  The exchange ratio of the Reverse Unit Split is 1-for-15 and will be effective on November 9, 2020. The common units will begin trading on a split-adjusted basis on November 10, 2020.
Common limited partner capital (in shares), outstanding			3,774,992		56,624,887
Subsequent Event | Summit Midstream GP, LLC | NYSE | Reverse Unit Split
Subsequent Event [Line Items]
Minimum bid price for continued listing | $ / shares	$ 1
Subsequent Event | TL Restructuring | SMP Holding
Subsequent Event [Line Items]
Percent of term loan lenders agree to term loan restructuring		100.00%
Common units issued to the lenders of term loan				34,600,000
2025 Senior Notes | Subsequent Event
Subsequent Event [Line Items]
Senior notes repurchased | $		$ 95.6
Total cash consideration | $		$ 64.8