Summit Midstream Partners (SMLP) 10-Q 9 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Entity Information [Line Items]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	1,549,922
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	SMLP
Common units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		73,356,950
General Partner Units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,490,999

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 370	$ 1,430
Accounts receivable	85,458	72,301
Other current assets	4,360	4,327
Total current assets	90,188	78,058
Property, plant and equipment, net	1,911,630	1,795,129
Intangible assets, net	281,207	301,345
Goodwill	16,211	16,211
Investment in equity method investees	660,254	690,485
Other noncurrent assets	18,566	13,565
Total assets	2,978,056	2,894,793
Current liabilities:
Trade accounts payable	22,569	16,375
Accrued expenses	18,347	12,499
Due to affiliate	13	1,088
Deferred revenue	11,152	4,000
Ad valorem taxes payable	8,223	8,329
Accrued interest	15,285	12,310
Accrued environmental remediation	2,702	3,130
Other current liabilities	10,388	11,258
Total current liabilities	88,679	68,989
Long-term debt	1,175,313	1,051,192
Deferred Purchase Price Obligation	416,718	362,959
Noncurrent deferred revenue	39,624	12,707
Noncurrent accrued environmental remediation	1,182	2,214
Other noncurrent liabilities	5,525	7,063
Total liabilities	1,727,041	1,505,124
Commitments and contingencies (Note 16)
Series A Preferred Units (300,000 units issued and outstanding at September 30, 2018 and December 31, 2017)	300,741	294,426
Common limited partner capital (73,355,775 units issued and outstanding at September 30, 2018 and 73,085,996 units issued and outstanding at December 31, 2017)	913,913	1,056,510
General Partner interests (1,490,999 units issued and outstanding at September 30, 2018 and December 31, 2017)	25,380	27,920
Noncontrolling interest	10,981	10,813
Total partners' capital	1,251,015	1,389,669
Total liabilities and partners' capital	$ 2,978,056	$ 2,894,793

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Series A preferred unitholders, issued	300,000	300,000
Series A preferred unitholders, outstanding	300,000	300,000
Common limited partner capital (in shares), issued	73,355,775	73,085,996
Common limited partner capital (in shares), outstanding	73,355,775	73,085,996
General partner interests (in shares), issued	1,490,999	1,490,999
General partner interests (in shares), outstanding	1,490,999	1,490,999

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 127,479	$ 124,945	$ 372,982	$ 362,542
Costs and expenses:
Cost of natural gas and NGLs	$ 26,879	$ 18,177	$ 71,549	$ 36,328
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 24,382	$ 22,303	$ 73,452	$ 70,011
General and administrative	11,740	13,289	39,666	40,370
Depreciation and amortization	26,743	28,927	80,204	86,184
Transaction costs	0	0	0	119
Loss (gain) on asset sales, net	6	460	(6)	530
Long-lived asset impairment	1,540	1,290	2,127	1,577
Total costs and expenses	91,290	84,446	266,992	235,119
Other income	58	79	78	214
Interest expense	(14,862)	(17,614)	(44,821)	(51,883)
Early extinguishment of debt	0	0	0	(22,020)
Deferred Purchase Price Obligation	37,204	70,499	(53,759)	54,674
Income before income taxes and (loss) income from equity method investees	58,589	93,463	7,488	108,408
Income tax benefit (expense)	35	(176)	(88)	(417)
(Loss) income from equity method investees	(1,169)	350	(3,703)	(3,691)
Net income	57,455	93,637	3,697	104,300
Net income attributable to noncontrolling interest	25	91	168	282
Net income attributable to SMLP	57,430	93,546	3,529	104,018
Less net income attributable to General Partner, including IDRs	3,279	3,999	6,477	8,442
Net income (loss) attributable to limited partners	54,151	89,547	(2,948)	95,576
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners	7,125	0	21,375	0
Common units
Costs and expenses:
Net income (loss) attributable to limited partners	$ 47,026	$ 89,547	$ (24,323)	$ 95,576
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.64	$ 1.23	$ (0.33)	$ 1.32
Diluted (in dollars per share)	$ 0.64	$ 1.22	$ (0.33)	$ 1.31
Weighted-average limited partner units outstanding:
Basic (shares)	73,356	73,059	73,283	72,583
Diluted (shares)	73,756	73,433	73,283	72,901
Gathering Services and Related Fees
Revenues:
Total revenues	$ 86,427	$ 96,070	$ 260,373	$ 298,884
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	34,017	22,940	92,025	44,655
Other Revenues
Revenues:
Total revenues	$ 7,035	$ 5,935	$ 20,584	$ 19,003

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Adjustment	Noncontrolling interest	Noncontrolling interestAdjustment	Common	CommonAdjustment	General Partner	General PartnerAdjustment	Limited partners, Series A Preferred Units	Limited partners, Series A Preferred UnitsAdjustment
Beginning balance at Dec. 31, 2016	$ 1,169,673		$ 11,247		$ 1,129,132		$ 29,294
Net income (loss)	104,300		282		95,576		8,442
Distributions to unitholders	(134,066)		0		(125,052)		(9,014)
Unit-based compensation	5,902		0		5,902		0
Tax withholdings on vested SMLP LTIP awards	(2,051)		0		(2,051)		0
ATM Program issuances, net of costs	17,251		0		17,251		0
Contribution from General Partner	465		0		0		465
Other	(166)		0		(166)		0
Ending balance at Sep. 30, 2017	1,161,308		11,529		1,120,592		29,187
January 1, 2018 impact of Topic 606day 1 adoption	4,214		0		4,130		84		$ 0
Beginning balance at Dec. 31, 2017	1,389,669	$ 1,393,883	10,813	$ 10,813	1,056,510	$ 1,060,640	27,920	$ 28,004	294,426	$ 294,426
Net income (loss)	3,697		168		(24,323)		6,477		21,375
Distributions to unitholders	(149,734)		0		(126,383)		(9,101)		(14,250)
Unit-based compensation	5,948		0		5,948		0		0
Tax withholdings on vested SMLP LTIP awards	(1,840)		0		(1,840)		0		0
Other	(939)		0		(129)		0		(810)
Ending balance at Sep. 30, 2018	$ 1,251,015		$ 10,981		$ 913,913		$ 25,380		$ 300,741

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 3,697	$ 104,300
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	79,752	85,732
Amortization of debt issuance costs	3,184	3,117
Deferred Purchase Price Obligation	53,759	(54,674)
Unit-based and noncash compensation	6,188	5,973
Loss from equity method investees	3,703	3,691
Distributions from equity method investees	26,528	28,715
Loss (gain) on asset sales, net	(6)	530
Long-lived asset impairment	2,127	1,577
Early extinguishment of debt	0	22,020
Write-off of debt issuance costs	0	302
Changes in operating assets and liabilities:
Accounts receivable	(11,557)	36,097
Trade accounts payable	(2,991)	1,200
Accrued expenses	5,848	2,726
Due (to) from affiliate	(1,075)	256
Deferred revenue, net	5,160	(39,671)
Ad valorem taxes payable	(106)	(2,470)
Accrued interest	2,975	2,700
Accrued environmental remediation, net	(3,060)	(2,935)
Other, net	(7,634)	(2,689)
Net cash provided by operating activities	166,492	196,497
Cash flows from investing activities:
Capital expenditures	(137,033)	(86,206)
Proceeds from asset sale	496	2,300
Contributions to equity method investees	0	(21,581)
Other, net	(209)	(579)
Net cash provided by (used in) investing activities	(136,746)	(106,066)
Cash flows from financing activities:
Distributions to unitholders		(134,066)
Borrowings under Revolving Credit Facility	202,000	177,500
Repayments under Revolving Credit Facility	(79,000)	(319,500)
Debt issuance costs	(334)	(15,891)
Payment of redemption and call premiums on senior notes	0	(17,913)
Proceeds from ATM Program common unit issuances, net of costs	0	17,251
Contribution from General Partner	0	465
Issuance of senior notes	0	500,000
Tender and redemption of senior notes	0	(300,000)
Other, net	(3,738)	(2,794)
Net cash provided by (used in) financing activities	(30,806)	(94,948)
Net change in cash and cash equivalents	(1,060)	(4,517)
Cash and cash equivalents, beginning of period	1,430	7,428
Cash and cash equivalents, end of period	370	2,911
Supplemental cash flow disclosures:
Cash interest paid	44,126	47,410
Less capitalized interest	5,536	1,562
Interest paid (net of capitalized interest)	38,590	45,848
Cash paid for taxes	175	0
Noncash investing and financing activities
Capital expenditures in trade accounts payable (period-end accruals)	20,977	13,647
Capital expenditures relating to contributions in aid of construction for Topic 606 day 1 adoption	33,123	0
Common units
Cash flows from financing activities:
Distributions to unitholders	(135,484)	(134,066)
Series A Preferred Units
Cash flows from financing activities:
Distributions to unitholders	$ (14,250)	$ 0

ORGANIZATION, BUSINESS OPERATIO

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION	9 Months Ended
	Sep. 30, 2018
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 in connection with its IPO of common limited partner units. SMLP is a growth-oriented limited partnership focused on developing, owning and operating midstream energy infrastructure assets that are strategically located in the core producing areas of unconventional resource basins, primarily shale formations, in the continental United States. Our business activities are conducted through various operating subsidiaries, each of which is owned or controlled by our wholly owned subsidiary holding company, Summit Holdings, a Delaware limited liability company. References to the "Partnership," "we," or "our" refer collectively to SMLP and its subsidiaries. The General Partner, a Delaware limited liability company, manages our operations and activities. Summit Investments, a Delaware limited liability company, is the ultimate owner of our General Partner and has the right to appoint the entire Board of Directors. Summit Investments is controlled by Energy Capital Partners. In addition to its approximate Neither SMLP nor its subsidiaries have any employees. All of the personnel that conduct our business are employed by Summit Investments, but these individuals are sometimes referred to as our employees. Business Operations. We provide natural gas gathering, treating and processing services as well as crude oil and produced water gathering services pursuant to primarily long-term, fee-based agreements with our customers. Our results are driven primarily by the volumes of natural gas that we gather, treat, compress and process as well as by the volumes of crude oil and produced water that we gather. We are the owner-operator of or have significant ownership interests in the following gathering systems: • Summit Utica, a natural gas gathering system operating in the Appalachian Basin, which includes the Utica and Point Pleasant shale formations in southeastern Ohio; • Ohio Gathering, a natural gas gathering system and a condensate stabilization facility operating in the Appalachian Basin, which includes the Utica and Point Pleasant shale formations in southeastern Ohio; • Polar and Divide, crude oil and produced water gathering systems and transmission pipelines located in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota; • Tioga Midstream, crude oil, produced water and associated natural gas gathering systems operating in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota; • Bison Midstream, an associated natural gas gathering system operating in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota; • Grand River, a natural gas gathering and processing system located in the Piceance Basin, which includes the Mesaverde formation and the Mancos and Niobrara shale formations in western Colorado and eastern Utah; • Niobrara G&P, an associated natural gas gathering and processing system operating in the DJ Basin, which includes the Niobrara and Codell shale formations in northeastern Colorado; • DFW Midstream, a natural gas gathering system operating in the Fort Worth Basin, which includes the Barnett Shale formation in north-central Texas; • Mountaineer Midstream, a natural gas gathering system operating in the Appalachian Basin, which includes the Marcellus Shale formation in northern West Virginia; and • Summit Permian, an associated natural gas gathering and processing system and interstate natural gas transportation pipeline under development in the northern Delaware Basin, which includes the Wolfcamp and Bone Spring formations, in southeastern New Mexico. In February 2016, the Partnership and SMP Holdings, a wholly owned subsidiary of Summit Investments, entered into a contribution agreement (the "Contribution Agreement") pursuant to which SMP Holdings agreed to contribute to the Partnership substantially all of its limited partner interest in OpCo, a Delaware limited partnership that owns (i) In December 2017, Niobrara G&P, the associated natural gas gathering and processing assets held by Meadowlark Midstream, were contributed to Summit Niobrara, a newly formed entity. Concurrent with this contribution (i) a subsidiary of SMLP purchased the remaining 1% ownership interest in Summit Niobrara held by Summit Epping, LLC; and (ii) 100% of the ownership interests in Summit Niobrara were contributed to Grand River Gathering, LLC (“Grand River”), after which Summit Niobrara became a wholly owned subsidiary of Grand River. Summit Marketing provides natural gas and crude oil marketing services in and around our gathering systems. Presentation and Consolidation. We prepare our unaudited condensed consolidated financial statements in accordance with GAAP as established by the FASB. We make estimates and assumptions that affect the reported amounts of assets and liabilities at the balance sheet dates, including fair value measurements, the reported amounts of revenue and expense and the disclosure of contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates. These unaudited condensed consolidated financial statements have been prepared pursuant to the rules and the regulations of the SEC. Certain information and note disclosures normally included in the annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. We believe that the disclosures made are adequate to make the information not misleading. In the opinion of management, the unaudited condensed consolidated financial statements contain all adjustments, including normal recurring adjustments, which are necessary to fairly present the unaudited condensed consolidated balance sheet as of September 30, 2018, the unaudited condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017 and the unaudited condensed consolidated statements of partners’ capital and cash flows for the nine months ended September 30, 2018 and 2017. The balance sheet at December 31, 2017 included herein was derived from our audited financial statements, but does not include all disclosures required by GAAP. See Notes 2 and 3 for the impact relating to the adoption of the new revenue standard. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto that are included in our annual report on Form 10-K for the year ended December 31, 2017, as filed with the SEC on February 26, 2018 (the "2017 Annual Report"). The results of operations for an interim period are not necessarily indicative of results expected for a full year.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Except for the changes below, there have been no changes to our significant accounting policies since December 31, 2017. Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. We review new pronouncements to determine the impact, if any, on our financial statements. Accounting standards that have or could possibly have a material effect on our financial statements are discussed below. Recently Adopted Accounting Pronouncements . We have recently adopted the following accounting pronouncements: • ASU No. 2014-09 Revenue from Contracts with Customers (“Topic 606”). We adopted Topic 606 with a date of initial application of January 1, 2018. We applied Topic 606 by recognizing the cumulative effect of initially applying Topic 606 as an adjustment to the opening balance of partners’ capital at January 1, 2018. The comparative information has not been adjusted and is reported under the accounting standards in effect for those periods. For contracts where we perform gathering services and earn a per-unit fee which is recognized at a point in time, revenue is recognized over time as the service is performed and results in revenue recognition materially consistent with historical GAAP. In addition, our contracts generally contain forms of variable consideration, which will likely be constrained as the volumes are susceptible to factors outside of our control and influence. As a result of applying the constraint guidance, timing of revenue recognition will be materially consistent with historical GAAP. Prior to the adoption of Topic 606, contributions in aid of construction were recognized as a reduction to our cost basis of property, plant and equipment and facility fees were recognized as revenue when the amounts were billed. Upon adoption of Topic 606, the contributions in aid of construction amounts previously received were capitalized to property, plant and equipment, net of any accumulated depreciation, and will be depreciated over the remaining useful lives. Any future contributions in aid of construction will be recognized as revenue over the remaining term of the respective contract in accordance with Topic 606. Additionally, facility fees will be deferred and recognized over the contract term. There are certain percent-of-proceeds contracts within our Williston Basin reportable segment where we previously recognized revenue for services provided to producers in gathering services and related fees. Such amounts which were previously presented gross in gathering services and related fees are presented net within cost of natural gas and NGLs. This change did not have any impact on our net income (loss), cash flows, or the amount we present as segment adjusted EBITDA. For contracts containing MVC arrangements with banking mechanisms we previously deferred revenue. Under Topic 606, the recognition of revenue was accelerated. This acceleration totaled $16.7 million and is included in the Topic 606 day one adjustment amounts below in deferred revenue. The cumulative effect of the changes made to our consolidated January 1, 2018 balance sheet for the adoption of Topic 606 was as follows: Balance at December 31, 2017 Adjustments Due to Topic 606 Balance at January 1, 2018 (In thousands) Assets Property, plant and equipment, net $ 1,795,129 $ 33,123 $ 1,828,252 Liabilities Deferred revenue, current 4,000 6,088 10,088 Deferred revenue, noncurrent 12,707 22,821 35,528 Partners' Capital (1) 1,084,430 4,214 1,088,644 ________ (1) Includes common limited partner capital and general partner interests. Impact on financial statements The following tables summarize the impact of Topic 606 adoption on our unaudited condensed consolidated financial statements. Unaudited condensed consolidated balance sheet September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Assets Accounts receivable $ 85,458 $ 76,656 $ 8,802 Other noncurrent assets 18,566 12,566 6,000 Property, plant and equipment, net 1,911,630 1,874,388 37,242 Liabilities Deferred revenue, current 11,152 4,071 7,081 Deferred revenue, noncurrent 39,624 10,065 29,559 Partners' Capital (1) 939,293 923,889 15,404 ________ (1) Includes common limited partner capital and general partner interests. Unaudited condensed consolidated statement of operations Three months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 86,427 $ 83,351 $ 3,076 Costs and expenses Cost of natural gas and NGLs 26,879 30,307 (3,428 ) Depreciation and amortization 26,743 26,373 370 Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 260,373 $ 255,546 $ 4,827 Costs and expenses Cost of natural gas and NGLs 71,549 81,468 (9,919 ) Depreciation and amortization 80,204 79,219 985 Unaudited condensed consolidated statement of cash flows Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Cash flows from operating activities: Net income (loss) $ 3,697 $ (10,064 ) $ 13,761 Adjustments to reconcile net loss to net cash provided by operating activities: Depreciation and amortization 79,752 78,767 985 Changes in operating assets and liabilities: Accounts receivable (11,557 ) (2,755 ) (8,802 ) Other, net (7,634 ) (1,634 ) (6,000 ) Deferred revenue, net 5,160 5,104 56 • ASU No. 2017-04 Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"). ASU 2017-04 simplifies the subsequent measurement of goodwill by, among other things, eliminating step two from the goodwill impairment test. ASU 2017-04 is effective for public companies for fiscal years beginning after December 15, 2019 and it specifies the amendments in ASU 2017-04 should be applied on a prospective basis. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We adopted the provisions of ASU 2017-04 effective January 1, 2018. The adoption of this standard had no impact on our consolidated financial statements. Accounting Pronouncements Pending Adoption • ASU No. 2016-02 Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 requires that lessees recognize all leases on the balance sheet, with the exception of short-term leases. A lease liability will be recorded for the obligation of a lessee to make lease payments arising from a lease. A right-of-use asset will be recorded which represents the lessee’s right to use, or to control the use of, a specified asset for a lease term. ASU 2016-02 is effective for public companies for fiscal years beginning after December 15, 2018, and requires the modified retrospective approach for transition. We are currently evaluating the provisions of ASU 2016-02 to determine its impact on our financial statements and related disclosures and will adopt its provisions effective January 1, 2019. We expect to utilize certain practical expedients including (i) not being required to reassess whether any expired or existing contracts are or contain leases; (ii) not being required to reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with Topic 840 will be classified as operating leases, and all existing leases that were classified as capital leases in accordance with Topic 840 will be classified as finance leases); and (iii) not being required to reassess initial direct costs for any existing leases. • ASU No. 2018-01 Leases: Land Easement Practical Expedient for Transition to Topic 842 (“ASU 2018-01”). ASU 2018-01 provides an optional transition practical expedient to not evaluate existing or expired land easements that were not previously accounted for as leases under the current lease guidance in Topic 840. Upon adoption of Topic 842, an entity that elects this practical expedient should evaluate new or modified land easements under Topic 842 beginning at the date the entity adopts Topic 842. We expect to adopt the optional transition practical expedient of ASU 2018-01 effective January 1, 2019. • ASU No. 2018-13 Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 updates the disclosure requirements on fair value measurements including new disclosures for the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 modifies existing disclosures including clarifying the measurement uncertainty disclosure. ASU 2018-13 removes certain existing disclosure requirements including the amount and reasons for transfers between Level 1 and Level 2 fair value measurements and the policy for the timing of transfer between levels. We are currently evaluating the provisions of ASU 2018-13 to determine its impact on our financial statements and related disclosures and will adopt its provisions effective January 1, 2020.

REVENUE

REVENUE	9 Months Ended
	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
REVENUE	3. REVENUE The majority of our revenue is derived from long-term, fee-based contracts with original terms of up to 25 years. We account for revenue in accordance with Topic 606, which we adopted on January 1, 2018, using the modified retrospective method. See Note 2 for further discussion of the adoption, including the impact on our unaudited condensed consolidated financial statements. We recognize revenue earned from fee-based gathering, treating and processing services in gathering services and related fees. We also earn revenue in the Williston Basin reporting segment from the sale of physical natural gas purchased from our customers under certain percent-of-proceeds arrangements. Under Topic 606, these gathering fee contracts are presented net within cost of natural gas and NGLs. We sell natural gas that we retain from certain DFW Midstream customers to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate retained from our gathering services at Grand River. Revenues from the sale of natural gas and condensate are recognized in natural gas, NGLs and condensate sales; the associated expense is included in operation and maintenance expense. Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis, with the revenue component recognized in other revenues. The transaction price in our contracts is primarily based on the volume of natural gas, crude oil or produced water transferred by our gathering systems to the customer’s agreed upon delivery point multiplied by the contractual rate. For contracts that include MVCs, variable consideration up to the MVC will be included in the transaction price. For contracts that do not include MVCs, we do not estimate variable consideration because the performance obligations are completed and settled on a daily basis. For contracts containing noncash consideration such as fuel received in-kind, we measure the transaction price at the point of sale when the volume, mix and market price of the commodities are known. We have contracts with MVCs that are variable and constrained. Contracts with MVCs are reviewed on a quarterly basis and adjustments to those estimates are made during each respective reporting period, if necessary. The transaction price is allocated if the contract contains more than one performance obligation such as contracts that include MVCs. The transaction price allocated is based on the MVC for the applicable measurement period. Performance obligations. The majority of our contracts have a single performance obligation which is either to provide gathering services (an integrated service) or sell natural gas, NGLs and condensate, which are both satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. We also have certain contracts with multiple performance obligations. They include an option for the customer to acquire additional services such as contracts containing MVCs. These performance obligations would also be satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. In these instances, we allocate the contract’s transaction price to each performance obligation using our best estimate of the standalone selling price of each service in the contract. Performance obligations for gathering services are generally satisfied over time. We utilize either an output method (i.e., measure of progress) for guaranteed, stand-ready service contracts or an asset / system delivery time estimate for non-guaranteed, as-available service contracts. Performance obligations for the sale of natural gas, NGLs and condensate are satisfied at a point in time. There are no significant judgments for these transactions because the customer obtains control based on an agreed upon delivery point. Certain of our gathering and/or processing agreements provide for monthly, annual or multi-year MVCs. Under these MVCs, our customers agree to ship and/or process a minimum volume of production on our gathering systems or to pay a minimum monetary amount over certain periods during the term of the MVC. A customer must make a shortfall payment to us at the end of the contracted measurement period if its actual throughput volumes are less than its MVC for that period. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent contracted measurement periods to the extent that such customer's throughput volumes in a subsequent contracted measurement period exceed its MVC for that contracted measurement period. We recognize customer obligations under their MVCs as revenue and contract assets when (i) we consider it remote that the customer will utilize shortfall payments to offset gathering or processing fees in excess of its MVCs in subsequent periods; (ii) the customer incurs a shortfall in a contract with no banking mechanism or claw back provision; (iii) the customer’s banking mechanism has expired; or (iv) it is remote that the customer will use its unexercised right. Our services are typically billed on a monthly basis and we do not offer extended payment terms. We do not have contracts with financing components. The following table presents estimated revenue expected to be recognized during the remainder of 2018 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments. We applied the practical expedient in paragraph 606-10-50-14 of Topic 606 for certain arrangements that we consider optional purchases (i.e., there is no enforceable obligation for the customer to make purchases) and those amounts are excluded from the table. 2018 2019 2020 2021 2022 Thereafter (In thousands) Gathering services and related fees $ 84,164 $ 127,743 $ 122,429 $ 102,777 $ 83,648 $ 174,825 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 4. Reportable Segments Three months ended September 30, 2018 Utica Shale Williston Basin Piceance / DJ Basins Barnett Shale Marcellus Shale Total reportable segments All other segments Total (In thousands) Major products/services lines Gathering services and related fees $ 7,974 $ 18,020 $ 36,743 $ 18,318 $ 7,150 $ 88,205 $ (1,778 ) $ 86,427 Natural gas, NGLs and condensate sales — 7,953 3,650 789 — 12,392 21,625 34,017 Other revenues — 3,037 2,072 1,913 — 7,022 13 7,035 Total $ 7,974 $ 29,010 $ 42,465 $ 21,020 $ 7,150 $ 107,619 $ 19,860 $ 127,479 Reportable Segments Nine months ended September 30, 2018 Utica Shale Williston Basin Piceance / DJ Basins Barnett Shale Marcellus Shale Total reportable segments All other segments Total (In thousands) Major products/services lines Gathering services and related fees $ 28,437 $ 58,792 $ 108,207 $ 46,035 $ 23,025 $ 264,496 $ (4,123 ) $ 260,373 Natural gas, NGLs and condensate sales — 23,149 12,650 1,715 — 37,514 54,511 92,025 Other revenues — 8,909 6,187 5,595 — 20,691 (107 ) 20,584 Total $ 28,437 $ 90,850 $ 127,044 $ 53,345 $ 23,025 $ 322,701 $ 50,281 $ 372,982 Contract balances. Contract assets relate to our rights to consideration for work completed but not billed at the reporting date and consist of the estimated MVC shortfall payments expected from our customers and unbilled activity associated with contributions in aid of construction. Contract assets are transferred to trade receivables when the rights become unconditional. The following table provides information about contract assets from contracts with customers: September 30, 2018 (In thousands) Contract assets, December 31, 2017 $ — Net impact of Topic 606 day 1 adoption 3,514 Additions 14,906 Transfers out (7,169 ) Contract assets, September 30, 2018 $ 11,251 As of September 30, 2018, receivables with customers totaled $70.8 million and contract assets totaled $11.3 million which were included in the accounts receivable caption on the unaudited condensed consolidated balance sheet. In addition, long-term contract assets of $6.0 million, which are excluded from the table above, were included in the other noncurrent assets caption on the unaudited condensed consolidated balance sheet. Contract liabilities (deferred revenue) relate to the advance consideration received from customers primarily for contributions in aid of construction. We recognize contract liabilities under these arrangements in revenue over the contract period. For the three and nine months ended September 30, 2018, we recognized $2.8 million and $7.8 million of gathering services and related fees which was included in the contract liability balance as of the beginning of the period. See Note 9 for additional details.

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	4. SEGMENT INFORMATION As of September 30, 2018, our reportable segments are: • the Utica Shale, which is served by Summit Utica; • Ohio Gathering, which includes our ownership interest in OGC and OCC; • the Williston Basin, which is served by Polar and Divide, Tioga Midstream and Bison Midstream; • the Piceance/DJ Basins, which is served by Grand River and Niobrara G&P; • the Barnett Shale, which is served by DFW Midstream; and • the Marcellus Shale, which is served by Mountaineer Midstream. Each of our reportable segments provides midstream services in a specific geographic area. Our reportable segments reflect the way in which we internally report the financial information used to make decisions and allocate resources in connection with our operations. The Ohio Gathering reportable segment includes our investment in OGC and OCC (see Note 8). Income or loss from equity method investees, as reflected on the statements of operations, solely relates to Ohio Gathering and is recognized and disclosed on a one-month lag (see Note 8). No other line items in the statements of operations or cash flows, as disclosed in the tables below, include results for our investment in Ohio Gathering. Corporate and Other represents those results that are: (i) not specifically attributable to a reportable segment; (ii) not individually reportable; or (iii) not allocated to our reportable segments for the purpose of evaluating their performance, including certain general and administrative expense items, natural gas and crude oil marketing services, and transaction costs. Assets by reportable segment follow. September 30, 2018 December 31, 2017 (In thousands) Assets: Utica Shale $ 209,105 $ 212,311 Ohio Gathering 660,254 690,485 Williston Basin 529,370 512,860 Piceance/DJ Basins 839,166 798,722 Barnett Shale 380,161 383,306 Marcellus Shale 210,509 217,362 Total reportable segment assets 2,828,565 2,815,046 Corporate and Other 152,375 79,996 Eliminations (2,884 ) (249 ) Total assets $ 2,978,056 $ 2,894,793 Revenues by reportable segment follow. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Revenues (1): Utica Shale $ 7,974 $ 9,727 $ 28,437 $ 28,979 Williston Basin 29,010 27,821 90,850 123,820 Piceance/DJ Basins 42,465 53,875 127,044 122,446 Barnett Shale 21,020 16,694 53,345 55,340 Marcellus Shale 7,150 8,160 23,025 22,429 Total reportable segments revenue 107,619 116,277 322,701 353,014 Corporate and Other 23,636 11,816 57,234 14,964 Eliminations (3,776 ) (3,148 ) (6,953 ) (5,436 ) Total revenues $ 127,479 $ 124,945 $ 372,982 $ 362,542 (1) Excludes revenues earned by Ohio Gathering due to equity method accounting. Counterparties accounting for more than 10% of total revenues were as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Percentage of total revenues (1)(2): Counterparty A - Piceance/DJ Basins 11 % 17 % 11 % * Counterparty B - Barnett Shale 12 % * 10 % * Counterparty C - Williston Basin * * * 16 % (1) Includes recognition of revenue that was previously deferred in connection with minimum volume commitments. (2) Excludes revenues earned by Ohio Gathering due to equity method accounting. * Less than 10% Depreciation and amortization, including the amortization expense associated with our favorable and unfavorable gas gathering contracts as reported in other revenues, by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Depreciation and amortization (1): Utica Shale $ 1,887 $ 1,818 $ 5,773 $ 5,213 Williston Basin 5,672 8,405 16,903 25,171 Piceance/DJ Basins 12,512 12,199 37,517 36,635 Barnett Shale (2) 3,760 3,735 11,276 11,259 Marcellus Shale 2,273 2,268 6,819 6,794 Total reportable segment depreciation and amortization 26,104 28,425 78,288 85,072 Corporate and Other 488 352 1,464 660 Total depreciation and amortization $ 26,592 $ 28,777 $ 79,752 $ 85,732 (1) Excludes depreciation and amortization recognized by Ohio Gathering due to equity method accounting. (2) Includes the amortization expense associated with our favorable and unfavorable gas gathering contracts as reported in other revenues. Cash paid for capital expenditures by reportable segment follow. Nine months ended September 30, 2018 2017 (In thousands) Cash paid for capital expenditures (1): Utica Shale $ 3,922 $ 21,425 Williston Basin 18,463 13,735 Piceance/DJ Basins 44,166 17,902 Barnett Shale 914 119 Marcellus Shale 557 628 Total reportable segment capital expenditures 68,022 53,809 Corporate and Other 69,011 32,397 Total cash paid for capital expenditures $ 137,033 $ 86,206 (1) Excludes cash paid for capital expenditures by Ohio Gathering due to equity method accounting. During the nine months ended September 30, 2018, Corporate included cash paid of $2.1 million for corporate purposes; the remainder represents capital expenditures for Summit Permian. We assess the performance of our reportable segments based on segment adjusted EBITDA. For the purpose of evaluating segment performance, we exclude the effect of Corporate and Other revenues and expenses, such as certain general and administrative expenses (including compensation-related expenses and professional services fees), natural gas and crude oil marketing services, transaction costs, interest expense, change in the Deferred Purchase Price Obligation fair value, early extinguishment of debt expense and income tax expense or benefit from segment adjusted EBITDA. Segment adjusted EBITDA by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 6,521 $ 8,412 $ 24,459 $ 25,857 Ohio Gathering 10,171 10,522 29,583 29,201 Williston Basin 19,849 16,212 54,849 51,176 Piceance/DJ Basins 29,831 30,008 86,739 86,256 Barnett Shale 10,818 10,838 31,770 35,924 Marcellus Shale 5,550 6,682 18,769 17,775 Total of reportable segments' measures of profit $ 82,740 $ 82,674 $ 246,169 $ 246,189 A reconciliation of income or loss before income taxes and income or loss from equity method investees to total of reportable segments' measures of profit or loss follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Reconciliation of income before income taxes and (loss) income from equity method investees to total of reportable segments' measures of profit: Income before income taxes and (loss) income from equity method investees $ 58,589 $ 93,463 $ 7,488 $ 108,408 Add: Corporate and Other 9,324 9,197 28,949 28,725 Interest expense 14,862 17,614 44,821 51,883 Early extinguishment of debt — — — 22,020 Deferred Purchase Price Obligation (37,204 ) (70,499 ) 53,759 (54,674 ) Depreciation and amortization 26,592 28,777 79,752 85,732 Proportional adjusted EBITDA for equity method investees 10,171 10,522 29,583 29,201 Adjustments related to MVC shortfall payments (2,999 ) (10,124 ) (6,541 ) (33,186 ) Adjustments related to capital reimbursement activity (106 ) — 49 — Unit-based and noncash compensation 1,965 1,974 6,188 5,973 Loss (gain) on asset sales, net 6 460 (6 ) 530 Long-lived asset impairment 1,540 1,290 2,127 1,577 Total of reportable segments' measures of profit $ 82,740 $ 82,674 $ 246,169 $ 246,189 For the three and nine months ended September 30, 2017, we included adjustments related to MVC shortfall payments in our calculation of segment adjusted EBITDA to account for (i) the net increases or decreases in deferred revenue for MVC shortfall payments and (ii) our inclusion of expected annual or multi-year MVC shortfall payments. With respect to the impact of a net change in deferred revenue for MVC shortfall payments, we treated increases in deferred revenue balances as a favorable adjustment to segment adjusted EBITDA, while decreases in deferred revenue balances were treated as an unfavorable adjustment to segment adjusted EBITDA. We also included a proportional amount of any historical and expected MVC shortfall payments in each quarter prior to the quarter in which we actually recognized the shortfall payment. For the three and nine months ended September 30, 2018, in accordance with Topic 606, adjustments related to MVC shortfall payments are recognized in gathering services and related fees (see Note 3). In accordance with Topic 606, contributions in aid of construction are recognized over the remaining term of the respective contract. We include adjustments related to capital reimbursement activity in our calculation of segment adjusted EBITDA to account for revenue recognized from contributions in aid of construction. Adjustments related to MVC shortfall payments by reportable segment follow. Three months ended September 30, 2018 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments 2,032 — (5,031 ) (2,999 ) Total adjustments related to MVC shortfall payments $ 2,032 $ — $ (5,031 ) $ (2,999 ) Three months ended September 30, 2017 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments 1,982 (12,200 ) 94 (10,124 ) Total adjustments related to MVC shortfall payments $ 1,982 $ (12,200 ) $ 94 $ (10,124 ) Nine months ended September 30, 2018 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments (1,354 ) (93 ) (5,094 ) (6,541 ) Total adjustments related to MVC shortfall payments $ (1,354 ) $ (93 ) $ (5,094 ) $ (6,541 ) Nine months ended September 30, 2017 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ (37,693 ) $ (1,978 ) $ — $ (39,671 ) Expected MVC shortfall adjustments 5,946 867 (328 ) 6,485 Total adjustments related to MVC shortfall payments $ (31,747 ) $ (1,111 ) $ (328 ) $ (33,186 )

PROPERTY, PLANT, AND EQUIPMENT,

PROPERTY, PLANT, AND EQUIPMENT, NET	9 Months Ended
	Sep. 30, 2018
Property Plant And Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT, NET	5. PROPERTY, PLANT AND EQUIPMENT, NET Details on property, plant and equipment follow. September 30, 2018 December 31, 2017 (In thousands) Gathering and processing systems and related equipment $ 2,031,540 $ 1,973,722 Construction in progress 194,472 78,850 Land and line fill 11,747 11,735 Other 42,286 40,262 Total 2,280,045 2,104,569 Less accumulated depreciation 368,415 309,440 Property, plant and equipment, net $ 1,911,630 $ 1,795,129 Depreciation expense and capitalized interest follow. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Depreciation expense $ 18,567 $ 18,837 $ 55,781 $ 55,935 Capitalized interest 2,451 644 5,536 1,562

AMORTIZING INTANGIBLE ASSETS AN

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT	9 Months Ended
	Sep. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT	6. AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT Details regarding our intangible assets and the unfavorable gas gathering contract (included in other noncurrent liabilities), all of which are subject to amortization, follow. September 30, 2018 Gross carrying amount Accumulated amortization Net (In thousands) Favorable gas gathering contracts $ 24,195 $ (13,517 ) $ 10,678 Contract intangibles 278,448 (137,426 ) 141,022 Rights-of-way 165,445 (35,938 ) 129,507 Total intangible assets $ 468,088 $ (186,881 ) $ 281,207 Unfavorable gas gathering contract $ 10,962 $ (10,692 ) $ 270 December 31, 2017 Gross carrying amount Accumulated amortization Net (In thousands) Favorable gas gathering contracts $ 24,195 $ (12,350 ) $ 11,845 Contract intangibles 278,448 (117,821 ) 160,627 Rights-of-way 159,986 (31,113 ) 128,873 Total intangible assets $ 462,629 $ (161,284 ) $ 301,345 Unfavorable gas gathering contract $ 10,962 $ (9,074 ) $ 1,888 We recognized amortization expense in other revenues as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Amortization expense – favorable gas gathering contracts $ (389 ) $ (390 ) $ (1,166 ) $ (1,167 ) Amortization expense – unfavorable gas gathering contract 540 540 1,618 1,619 We recognized amortization expense in costs and expenses as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Amortization expense – contract intangibles $ 6,535 $ 8,550 $ 19,605 $ 25,652 Amortization expense – rights-of-way 1,641 1,540 4,818 4,597 The estimated aggregate annual amortization expected to be recognized for the remainder of 2018 and each of the four succeeding fiscal years follows. Intangible assets Unfavorable gas gathering contract (In thousands) 2018 $ 8,562 $ 270 2019 33,321 — 2020 33,145 — 2021 29,453 — 2022 26,386 —

GOODWILL

GOODWILL	9 Months Ended
	Sep. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
GOODWILL	7. GOODWILL We evaluate goodwill for impairment annually on September 30. We also evaluate goodwill whenever events or circumstances indicate that it is more likely than not that the fair value of a reporting unit is less than its carrying value, including goodwill. We test goodwill for impairment by comparing the fair value of the reporting unit to its carrying value, including goodwill. If the reporting unit’s fair value exceeds its carrying value, including goodwill, we conclude that the goodwill of the reporting unit has not been impaired and no further work is performed. If we determine that the reporting unit’s carrying value, including goodwill, exceeds its fair value, we recognize the excess of the carrying value over the fair value as a goodwill impairment loss. We performed our annual goodwill impairment testing for the Mountaineer Midstream reporting unit as of September 30, 2018, using a combination of the income and market approaches. We determined that the fair value of the Mountaineer Midstream reporting unit substantially exceeded its carrying value, including goodwill; as such, there have been no impairments of goodwill during the nine months ended September 30, 2018. Fair Value Measurement. Our impairment determinations, in the context of (i) our annual impairment evaluations and (ii) our other-than-annual impairment evaluations involved significant assumptions and judgments, as discussed in the 2017 Annual Report. Differing assumptions regarding any of these inputs could have a significant effect on the various valuations. As such, the fair value measurements utilized within these models are classified as non-recurring Level 3 measurements in the fair value hierarchy because they are not observable from objective sources. Due to the volatility of the inputs used, we cannot predict the likelihood of any future impairment.

EQUITY METHOD INVESTMENTS

EQUITY METHOD INVESTMENTS	9 Months Ended
	Sep. 30, 2018
Equity Method Investments And Joint Ventures [Abstract]
EQUITY METHOD INVESTMENTS	8. EQUITY METHOD INVESTMENTS Ohio Gathering owns, operates and is currently developing midstream infrastructure consisting of a liquids-rich natural gas gathering system, a dry natural gas gathering system and a condensate stabilization facility in the Utica Shale in southeastern Ohio. Ohio Gathering provides gathering services pursuant to primarily long-term, fee-based gathering agreements, which include acreage dedications. In September 2018, an impairment loss was recognized by Ohio Gathering. Although we recognize activity for Ohio Gathering on a one-month lag, we recorded the impairment loss in our results of operations for the third quarter of 2018 because the information was available to us. We recorded our 40% share of the impairment loss, or $1.8 million, in September 2018 in loss from equity method investees in the unaudited condensed consolidated statements of operations. A reconciliation of our Investment in equity method investees, September 30, 2018 $ 660,254 September cash distributions 2,912 Impairment loss 1,837 Basis difference (120,170 ) Investment in equity method investees, net of basis difference, August 31, 2018 $ 544,833 For the three and nine months ended September 30, 2018, there were no contributions to Ohio Gathering. Summarized statements of operations information for OGC and OCC follow (amounts represent 100% of investee financial information). Results include gross asset impairments of $4.6 million and $16.9 million for the three and nine months ending September 30, 2018 and $8.7 million for the three and nine months ending September 30, 2017. Three months ended August 31, 2018 Three months ended August 31, 2017 OGC OCC OGC OCC (In thousands) Total revenues $ 37,180 $ 2,465 $ 35,144 $ 1,814 Total operating expenses 31,751 2,323 25,720 1,877 Net income (loss) 5,429 (5 ) 9,424 (204 ) Nine months ended August 31, 2018 Nine months ended August 31, 2017 OGC OCC OGC OCC (In thousands) Total revenues $ 106,263 $ 7,024 $ 103,302 $ 5,871 Total operating expenses 94,044 6,422 86,046 6,186 Net income (loss) 12,213 116 17,258 (1,396 )

DEFERRED REVENUE

DEFERRED REVENUE	9 Months Ended
	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
DEFERRED REVENUE	9. DEFERRED REVENUE A rollforward of current deferred revenue follows. Utica Shale Williston Basin Piceance/DJ Basins Barnett Shale Marcellus Shale Total current (In thousands) Current deferred revenue, December 31, 2017, as reported $ — $ — $ 4,000 $ — $ — $ 4,000 Net impact of Topic 606 day 1 adoption 18 1,017 3,396 1,619 38 6,088 Current deferred revenue, January 1, 2018 18 1,017 7,396 1,619 38 10,088 Additions 14 1,367 16,846 1,236 63 19,526 Less revenue recognized 14 985 16,186 1,214 63 18,462 Current deferred revenue, September 30, 2018 $ 18 $ 1,399 $ 8,056 $ 1,641 $ 38 $ 11,152 A rollforward of noncurrent deferred revenue follows. Utica Shale Williston Basin Piceance/DJ Basins Barnett Shale Marcellus Shale Total noncurrent (In thousands) Noncurrent deferred revenue, December 31, 2017, as reported $ — $ — $ 12,707 $ — $ — $ 12,707 Net impact of Topic 606 day 1 adoption 39 4,215 10,017 8,217 333 22,821 Noncurrent deferred revenue, January 1, 2018 39 4,215 22,724 8,217 333 35,528 Additions — 1,851 9,014 2,323 — 13,188 Less reclassification to current deferred revenue 14 1,296 6,483 1,236 63 9,092 Noncurrent deferred revenue, September 30, 2018 $ 25 $ 4,770 $ 25,255 $ 9,304 $ 270 $ 39,624

DEBT

DEBT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
DEBT	10. DEBT Debt consisted of the following: September 30, 2018 December 31, 2017 (In thousands) Summit Holdings' variable rate senior secured Revolving Credit Facility (4.50% at September 30, 2018 and 4.07% at December 31, 2017) due May 2022 $ 384,000 $ 261,000 Summit Holdings' 5.5% senior unsecured notes due August 2022 300,000 300,000 Less unamortized debt issuance costs (1) (2,530 ) (2,910 ) Summit Holdings' 5.75% senior unsecured notes due April 2025 500,000 500,000 Less unamortized debt issuance costs (1) (6,157 ) (6,898 ) Total long-term debt $ 1,175,313 $ 1,051,192 (1) Issuance costs are being amortized over the life of the notes. Revolving Credit Facility. Summit Holdings has a senior secured revolving credit facility that allows for revolving loans, letters of credit and swing line loans. The Revolving Credit Facility has a $1.25 billion borrowing capacity, matures in May 2022, and includes a $250.0 million accordion feature. Bison Midstream and its subsidiaries, Grand River and its subsidiary, DFW Midstream, Summit Marketing, Summit Permian, Permian Finance, Summit Niobrara, OpCo, Summit Utica, Meadowlark Midstream, Tioga Midstream and SMLP fully and unconditionally and jointly and severally guarantee, and pledge substantially all of their assets in support of, the indebtedness outstanding under the Revolving Credit Facility. Borrowings under the Revolving Credit Facility bear interest, at the election of Summit Holdings, at a rate based on the alternate base rate (as defined in the credit agreement) plus an applicable margin ranging from 0.75% to 1.75% or the adjusted Eurodollar rate (as defined in the credit agreement) plus an applicable margin ranging from 1.75% to 2.75%, with the commitment fee ranging from 0.30% to 0.50% in each case based on our relative leverage at the time of determination. At September 30, 2018, the applicable margin under LIBOR borrowings was 2.25% and the interest rate was 4.50%. The unused portion of the Revolving Credit Facility totaled $866.0 million (subject to a commitment fee of 0.375%). As of September 30, 2018, we had As of and during the nine months ended September 30, 2018, we were in compliance with the Revolving Credit Facility's covenants. There were Senior Notes. In July 2014, Summit Holdings and its 100 owned finance subsidiary, Finance Corp. (together with Summit Holdings, the "Co-Issuers") co-issued $300.0 million of 5.5 senior unsecured notes maturing August 15, 2022 (the "5.5% Senior Notes" and, together with the 5.75 Senior Notes (defined below, the “Senior Notes”). In February 2017, the Co-Issuers completed a public offering of Bison Midstream and its subsidiaries, Grand River and its subsidiary, DFW Midstream, Summit Marketing, Summit Permian, Permian Finance and Summit Niobrara (collectively the "Guarantor Subsidiaries") and SMLP fully and unconditionally and jointly and severally guarantee the 5.5% Senior Notes and the 5.75% Senior Notes. The Senior Notes are not guaranteed by OpCo, Summit Utica, Meadowlark Midstream and Tioga Midstream (collectively, the "Non-Guarantor Subsidiaries"). There are no significant restrictions on the ability of SMLP or Summit Holdings to obtain funds from its subsidiaries by dividend or loan. Finance Corp. has had no assets or operations since inception in 2013. At no time have the Senior Notes been guaranteed by the Co-Issuers. As of and during the nine months ended September 30, 2018, we were in compliance with the covenants governing our Senior Notes. There were no defaults or events of default during the nine months ended September 30, 2018.

FINANCIAL INSTRUMENTS

FINANCIAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
FINANCIAL INSTRUMENTS	11. FINANCIAL INSTRUMENTS Concentrations of Credit Risk. Financial instruments that potentially subject us to concentrations of credit risk consist of cash and cash equivalents and accounts receivable. We maintain our cash and cash equivalents in bank deposit accounts that frequently exceed federally insured limits. We have not experienced any losses in such accounts and do not believe we are exposed to any significant risk. Accounts receivable primarily comprise amounts due for the gathering, treating and processing services we provide to our customers and also the sale of natural gas liquids resulting from our processing services. This industry concentration has the potential to impact our overall exposure to credit risk, either positively or negatively, in that our customers may be similarly affected by changes in economic, industry or other conditions. We monitor the creditworthiness of our counterparties and can require letters of credit for receivables from counterparties that are judged to have substandard credit, unless the credit risk can otherwise be mitigated. Our top Fair Value. The carrying amount of cash and cash equivalents, accounts receivable and trade accounts payable reported on the balance sheet approximates fair value due to their short-term maturities. The Deferred Purchase Price Obligation's carrying value is its fair value because carrying value represents the present value of the payment expected to be made in 2020. Our calculation of the Deferred Purchase Price Obligation involves significant assumptions and judgments. Differing assumptions regarding any of these inputs could have a material effect on the ultimate cash payment and the Deferred Purchase Price Obligation. As such, its fair value measurement is classified as a recurring Level 3 measurement in the fair value hierarchy because our assumptions and judgments are not observable from objective sources (see Note 17). The Deferred Purchase Price Obligation represents our only Level 3 financial instrument fair value measurement. A rollforward of our Level 3 liability measured at fair value on a recurring basis follows (in thousands). Level 3 liability, January 1, 2018 $ 362,959 Change in fair value 53,759 Level 3 liability, September 30, 2018 $ 416,718 A summary of the estimated fair value of our debt financial instruments follows. September 30, 2018 December 31, 2017 Carrying value Estimated fair value (Level 2) Carrying value Estimated fair value (Level 2) (In thousands) Summit Holdings 5.5% Senior Notes ($300.0 million principal) $ 297,470 $ 300,000 $ 297,090 $ 301,750 Summit Holdings 5.75% Senior Notes ($500.0 million principal) 493,843 481,250 493,102 501,667 The carrying value on the balance sheet of the Revolving Credit Facility is its fair value due to its floating interest rate. The fair value for the Senior Notes is based on an average of nonbinding broker quotes as of September 30, 2018 and December 31, 2017. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the Senior Notes.

PARTNERS' CAPITAL

PARTNERS' CAPITAL	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
PARTNERS' CAPITAL	12. PARTNERS' CAPITAL A rollforward of the number of common limited partner and General Partner units follows. Limited partners Series A Preferred Units Common General Partner Units, January 1, 2018 300,000 73,085,996 1,490,999 Net units issued under the SMLP LTIP — 269,779 — Units, September 30, 2018 300,000 73,355,775 1,490,999 At-the-market Program. In 2017, we executed a new equity distribution agreement and filed a prospectus and a prospectus supplement with the SEC for the issuance and sale from time to time of SMLP common units having an aggregate offering price of up to $150.0 million (the "ATM Program"). These sales will be made (i) pursuant to the terms of the equity distribution agreement between us and the sales agents named therein and (ii) by means of ordinary brokers' transactions at market prices, in block transactions or as otherwise agreed between us and the sales agents. Sales of our common units may be made in negotiated transactions or transactions that are deemed to be at-the-market offerings as defined by SEC rules During the three and nine months ended September 30, 2018, there were no Series A Preferred Units. In 2017, we issued 300,000 Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units (the “Series A Preferred Units”) representing limited partner interests in the Partnership at a price to the public of $1,000 per unit as described in the 2017 Annual Report. Noncontrolling Interest. We have recorded Summit Investments' indirect retained ownership interest in OpCo and its subsidiaries as a noncontrolling interest in the unaudited condensed consolidated financial statements. Cash Distributions Paid and Declared. We paid the following per-unit distributions during the three and nine months ended September 30: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Per-unit distributions to unitholders $ 0.575 $ 0.575 $ 1.725 $ 1.725 On October 25, 2018, the Board of Directors of our General Partner declared a distribution of $0.575 Incentive Distribution Rights. Our general partner also currently holds IDRs that entitle it to receive increasing percentage allocations, up to a maximum of 50 $0.46 per unit per quarter. Our payment of IDRs as reported in distributions to unitholders – general partner in the statement of partners' capital during the three and nine months ended September 30 follow. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) IDR payments $ 2,136 $ 2,127 $ 6,400 $ 6,333 For the purposes of calculating net income attributable to General Partner in the statements of operations and partners' capital, the financial impact of IDRs is recognized in respect of the quarter for which the distributions were declared. For the purposes of calculating distributions to unitholders in the statements of partners' capital and cash flows, IDR payments are recognized in the quarter in which they are paid.

EARNINGS PER UNIT

EARNINGS PER UNIT	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
EARNINGS PER UNIT	13. EARNINGS PER UNIT The following table details the components of EPU. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (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 $ 54,151 $ 89,547 $ (2,948 ) $ 95,576 Less net income attributable to Series A Preferred Units 7,125 — 21,375 — Net income (loss) attributable to common limited partners $ 47,026 $ 89,547 $ (24,323 ) $ 95,576 Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 73,356 73,059 73,283 72,583 Effect of nonvested phantom units 400 374 — 318 Weighted-average common units outstanding – diluted 73,756 73,433 73,283 72,901 Earnings (loss) per limited partner unit: Common unit – basic $ 0.64 $ 1.23 $ (0.33 ) $ 1.32 Common unit – diluted $ 0.64 $ 1.22 $ (0.33 ) $ 1.31 Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 1 — 2 55

UNIT-BASED AND NONCASH COMPENSA

UNIT-BASED AND NONCASH COMPENSATION	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
UNIT-BASED AND NONCASH COMPENSATION	14. UNIT-BASED AND NONCASH COMPENSATION SMLP Long-Term Incentive Plan. The SMLP LTIP provides for equity awards to eligible officers, employees, consultants and directors of our General Partner and its affiliates. Items to note: • In March 2018, we granted 515,358 phantom units and associated distribution equivalent rights to employees in connection with our annual incentive compensation award cycle. These awards had a grant date fair value of $15.25 and vest ratably over a three-year • Also in March 2018, 328,388 phantom units vested. • As of September 30, 2018, approximately 3.2 common units remained available for future issuance under the SMLP LTIP.

RELATED-PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
RELATED-PARTY TRANSACTIONS	15. RELATED-PARTY TRANSACTIONS Acquisitions. See Notes 11 and 16 of the 2017 Annual Report. Reimbursement of Expenses from General Partner. Our General Partner and its affiliates do not receive a management fee or other compensation in connection with the management of our business, but will be reimbursed for expenses incurred on our behalf. Under our Partnership Agreement, we reimburse our General Partner and its affiliates for certain expenses incurred on our behalf, including, without limitation, salary, bonus, incentive compensation and other amounts paid to our General Partner's employees and executive officers who perform services necessary to run our business. Our Partnership Agreement provides that our General Partner will determine in good faith the expenses that are allocable to us. The "Due to affiliate" line item on the consolidated balance sheet represents the payables to our General Partner for expenses incurred by it and paid on our behalf. Expenses incurred by the General Partner and reimbursed by us under our Partnership Agreement were as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Operation and maintenance expense $ 7,161 $ 6,792 $ 21,898 $ 20,404 General and administrative expense 7,220 6,840 22,818 23,030

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	16. COMMITMENTS AND CONTINGENCIES Operating Leases. We and Summit Investments lease certain office space and equipment to support our operations. We have determined that our leases are operating leases. We recognize total rent expense incurred or allocated to us in general and administrative expenses. Rent expense related to operating leases, including rent expense incurred on our behalf and allocated to us, was as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Rent expense $ 957 $ 1,009 $ 2,935 $ 2,811 Environmental Matters. Although we believe that we are in material compliance with applicable environmental regulations, the risk of environmental remediation costs and liabilities are inherent in pipeline ownership and operation. Furthermore, we can provide no assurances that significant environmental remediation costs and liabilities will not be incurred by the Partnership in the future. We are currently not aware of any material contingent liabilities that exist with respect to environmental matters, except as noted below. As described in the 2017 Annual Report, in 2015, Summit Investments learned of the rupture of a four-inch produced water gathering pipeline on the Meadowlark Midstream system near Williston, North Dakota. The incident, which was covered by Summit Investments' insurance policies, was subject to maximum coverage of A rollforward of the aggregate accrued environmental remediation liabilities follows. Total (In thousands) Accrued environmental remediation, January 1, 2018 $ 5,344 Payments made (3,060 ) Additional accruals 1,600 Accrued environmental remediation, September 30, 2018 $ 3,884 As of September 30, 2018, we have recognized (i) a current liability for remediation effort expenditures expected to be incurred within the next 12 months and (ii) a noncurrent liability for estimated remediation expenditures and fines expected to be incurred subsequent to September 30, 2019. Each of these amounts represent our best estimate for costs expected to be incurred. Neither of these amounts has been discounted to its present value. 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. As described in the 2017 Annual Report, in 2015 and 2016, the U.S. Department of Justice (“DOJ”) issued grand jury subpoenas to Summit Investments, the Partnership, our General Partner and Meadowlark Midstream requesting certain materials related to the incident. SMLP has continued to exchange information with the DOJ and is cooperating with the investigation. While we cannot predict the ultimate outcome of this matter with certainty for Summit Investments or Meadowlark Midstream, especially as it relates to any material liability as a result of any governmental proceeding related to the incident, we believe at this time that it is unlikely that SMLP or its General Partner will be subject to any material liability as a result of any governmental proceeding related to the rupture.

ACQUISITIONS AND DROP DOWN TRAN

ACQUISITIONS AND DROP DOWN TRANSACTIONS	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
ACQUISITIONS AND DROP DOWN TRANSACTIONS	17. ACQUISITIONS AND DROP DOWN TRANSACTIONS 2016 Drop Down. In 2016, SMLP acquired a controlling interest in OpCo, the entity which owns the 2016 Drop Down Assets. These assets include certain natural gas, crude oil and produced water gathering systems located in the Utica Shale, the Williston Basin and the DJ Basin, as well as ownership interests in a natural gas gathering system and a condensate stabilization facility, both located in the Utica Shale. The net consideration paid and recognized in connection with the 2016 Drop Down (i) consisted of a cash payment to SMP Holdings of The present value of the Deferred Purchase Price Obligation is reflected as a liability on our balance sheet until paid. As of September 30, 2018, Remaining Consideration was estimated to be $470.9 million We currently expect that the Deferred Purchase Price Obligation will be financed with a combination of (i) net proceeds from the issuance of equity securities by us, (ii) the net proceeds from the issuance of senior unsecured debt by us, (iii) borrowings under our Revolving Credit Facility and/or (iv) other internally generated sources of cash.

CONDENSED CONSOLIDATING FINANCI

CONDENSED CONSOLIDATING FINANCIAL INFORMATION	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
CONDENSED CONSOLIDATING FINANCIAL INFORMATION	18. CONDENSED CONSOLIDATING FINANCIAL INFORMATION The Senior Notes are fully and unconditionally guaranteed, jointly and severally, on a senior unsecured basis by SMLP and the Guarantor Subsidiaries (see Note 10). The following supplemental condensed consolidating financial information reflects SMLP's separate accounts, the combined accounts of the Co-Issuers, the combined accounts of the Guarantor Subsidiaries, the combined accounts of the Non-Guarantor Subsidiaries and the consolidating adjustments for the dates and periods indicated. For purposes of the following consolidating information each of SMLP and the Co-Issuers account for their subsidiary investments, if any, under the equity method of accounting. Condensed Consolidating Balance Sheets. Balance sheets as of September 30, 2018 and December 31, 2017 follow. September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Assets Cash and cash equivalents $ 29 $ 3 $ 330 $ 8 $ — $ 370 Accounts receivable 22 — 74,766 10,670 — 85,458 Other current assets 843 — 2,922 595 — 4,360 Due from affiliate — — 513,867 68,121 (581,988 ) — Total current assets 894 3 591,885 79,394 (581,988 ) 90,188 Property, plant and equipment, net 5,134 — 1,563,950 342,546 — 1,911,630 Intangible assets, net — — 255,317 25,890 — 281,207 Goodwill — — 16,211 — — 16,211 Investment in equity method investees — — — 660,254 — 660,254 Other noncurrent assets 3,320 9,184 6,062 — — 18,566 Investment in subsidiaries 2,082,686 3,432,198 — — (5,514,884 ) — Total assets $ 2,092,034 $ 3,441,385 $ 2,433,425 $ 1,108,084 $ (6,096,872 ) $ 2,978,056 Liabilities and Partners' Capital Trade accounts payable $ 219 $ — $ 18,523 $ 3,827 $ — $ 22,569 Accrued expenses 725 — 16,051 1,571 — 18,347 Due to affiliate 413,900 168,101 — — (581,988 ) 13 Deferred revenue — — 10,716 436 — 11,152 Ad valorem taxes payable 14 — 7,802 407 — 8,223 Accrued interest — 15,285 — — — 15,285 Accrued environmental remediation — — — 2,702 — 2,702 Other current liabilities 5,386 — 4,488 514 — 10,388 Total current liabilities 420,244 183,386 57,580 9,457 (581,988 ) 88,679 Long-term debt — 1,175,313 — — — 1,175,313 Deferred Purchase Price Obligation 416,718 — — — — 416,718 Noncurrent deferred revenue — — 37,802 1,822 — 39,624 Noncurrent accrued environmental remediation — — — 1,182 — 1,182 Other noncurrent liabilities 4,057 — 1,437 31 — 5,525 Total liabilities 841,019 1,358,699 96,819 12,492 (581,988 ) 1,727,041 Total partners' capital 1,251,015 2,082,686 2,336,606 1,095,592 (5,514,884 ) 1,251,015 Total liabilities and partners' capital $ 2,092,034 $ 3,441,385 $ 2,433,425 $ 1,108,084 $ (6,096,872 ) $ 2,978,056 December 31, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Assets Cash and cash equivalents $ 126 $ 75 $ 1,138 $ 91 $ — $ 1,430 Accounts receivable 22 — 65,842 6,437 — 72,301 Other current assets 1,188 — 2,697 442 — 4,327 Due from affiliate — — 493,067 22,030 (515,097 ) — Total current assets 1,336 75 562,744 29,000 (515,097 ) 78,058 Property, plant and equipment, net 4,206 — 1,442,333 348,590 — 1,795,129 Intangible assets, net — — 278,958 22,387 — 301,345 Goodwill — — 16,211 — — 16,211 Investment in equity method investees — — — 690,485 — 690,485 Other noncurrent assets 2,547 10,913 105 — — 13,565 Investment in subsidiaries 2,019,700 3,324,464 — — (5,344,164 ) — Total assets $ 2,027,789 $ 3,335,452 $ 2,300,351 $ 1,090,462 $ (5,859,261 ) $ 2,894,793 Liabilities and Partners' Capital Trade accounts payable $ 209 $ — $ 11,283 $ 4,883 $ — $ 16,375 Accrued expenses 928 — 10,592 979 — 12,499 Due to affiliate 263,935 252,250 — — (515,097 ) 1,088 Deferred revenue — — 4,000 — — 4,000 Ad valorem taxes payable — — 7,809 520 — 8,329 Accrued interest — 12,310 — — — 12,310 Accrued environmental remediation — — — 3,130 — 3,130 Other current liabilities 6,395 — 4,385 478 — 11,258 Total current liabilities 271,467 264,560 38,069 9,990 (515,097 ) 68,989 Long-term debt — 1,051,192 — — — 1,051,192 Deferred Purchase Price Obligation 362,959 — — — — 362,959 Deferred revenue — — 12,707 — — 12,707 Noncurrent accrued environmental remediation — — — 2,214 — 2,214 Other noncurrent liabilities 3,694 — 3,293 76 — 7,063 Total liabilities 638,120 1,315,752 54,069 12,280 (515,097 ) 1,505,124 Total partners' capital 1,389,669 2,019,700 2,246,282 1,078,182 (5,344,164 ) 1,389,669 Total liabilities and partners' capital $ 2,027,789 $ 3,335,452 $ 2,300,351 $ 1,090,462 $ (5,859,261 ) $ 2,894,793 Condensed Consolidating Statements of Operations. For the purposes of the following condensed consolidating statements of operations, we allocate general and administrative expenses recognized at the SMLP parent to the Guarantor Subsidiaries and Non-Guarantor Subsidiaries to reflect what those entities' results would have been had they operated on a stand-alone basis. Statements of operations for the three and nine months ended September 30, 2018 and 2017 follow. Three months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 73,014 $ 13,413 $ — $ 86,427 Natural gas, NGLs and condensate sales — — 34,017 — — 34,017 Other revenues — — 6,806 229 — 7,035 Total revenues — — 113,837 13,642 — 127,479 Costs and expenses: Cost of natural gas and NGLs — — 26,879 — — 26,879 Operation and maintenance — — 21,721 2,661 — 24,382 General and administrative — — 10,535 1,205 — 11,740 Depreciation and amortization 429 — 22,863 3,451 — 26,743 Loss on asset sales, net — — 1 5 — 6 Long-lived asset impairment — — 275 1,265 — 1,540 Total costs and expenses 429 — 82,274 8,587 — 91,290 Other income 58 — — — — 58 Interest expense — (14,862 ) — — — (14,862 ) Deferred Purchase Price Obligation 37,204 — — — — 37,204 Income (loss) before income taxes and loss from equity method investees 36,833 (14,862 ) 31,563 5,055 — 58,589 Income tax benefit 35 — — — — 35 Loss from equity method investees — — — (1,169 ) — (1,169 ) Equity in earnings of consolidated subsidiaries 20,587 35,449 — — (56,036 ) — Net income $ 57,455 $ 20,587 $ 31,563 $ 3,886 $ (56,036 ) $ 57,455 Three months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 82,152 $ 13,918 $ — $ 96,070 Natural gas, NGLs and condensate sales — — 22,940 — — 22,940 Other revenues — — 5,877 58 — 5,935 Total revenues — — 110,969 13,976 — 124,945 Costs and expenses: Cost of natural gas and NGLs — — 18,177 — — 18,177 Operation and maintenance — — 20,217 2,086 — 22,303 General and administrative — — 11,919 1,370 — 13,289 Depreciation and amortization 352 — 25,247 3,328 — 28,927 Transaction costs — — — — — — (Gain) loss on asset sales, net — — (82 ) 542 — 460 Long-lived asset impairment — — 696 594 — 1,290 Total costs and expenses 352 — 76,174 7,920 — 84,446 Other income 79 — — — — 79 Interest expense — (17,614 ) — — — (17,614 ) Deferred Purchase Price Obligation 70,499 — — — — 70,499 Income (loss) before income taxes and income from equity method investees 70,226 (17,614 ) 34,795 6,056 — 93,463 Income tax expense (176 ) — — — — (176 ) Income from equity method investees — — — 350 — 350 Equity in earnings of consolidated subsidiaries 23,587 41,201 — — (64,788 ) — Net income $ 93,637 $ 23,587 $ 34,795 $ 6,406 $ (64,788 ) $ 93,637 Nine months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 216,371 $ 44,002 $ — $ 260,373 Natural gas, NGLs and condensate sales — — 92,025 — — 92,025 Other revenues — — 20,042 542 — 20,584 Total revenues — — 328,438 44,544 — 372,982 Costs and expenses: Cost of natural gas and NGLs — — 71,549 — — 71,549 Operation and maintenance — — 66,095 7,357 — 73,452 General and administrative — — 34,786 4,880 — 39,666 Depreciation and amortization 1,305 — 68,500 10,399 — 80,204 (Gain) loss on asset sales, net — — (74 ) 68 — (6 ) Long-lived asset impairment — — 862 1,265 — 2,127 Total costs and expenses 1,305 — 241,718 23,969 — 266,992 Other income 78 — — — — 78 Interest expense — (44,821 ) — — — (44,821 ) Deferred Purchase Price Obligation (53,759 ) — — — — (53,759 ) (Loss) income before income taxes and loss from equity method investees (54,986 ) (44,821 ) 86,720 20,575 — 7,488 Income tax expense (88 ) — — — — (88 ) Loss from equity method investees — — — (3,703 ) — (3,703 ) Equity in earnings of consolidated subsidiaries 58,771 103,592 — — (162,363 ) — Net income $ 3,697 $ 58,771 $ 86,720 $ 16,872 $ (162,363 ) $ 3,697 Nine months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 252,344 $ 46,540 $ — $ 298,884 Natural gas, NGLs and condensate sales — — 44,655 — — 44,655 Other revenues — — 18,809 194 — 19,003 Total revenues — — 315,808 46,734 — 362,542 Costs and expenses: Cost of natural gas and NGLs — — 36,328 — — 36,328 Operation and maintenance — — 64,405 5,606 — 70,011 General and administrative — — 35,283 5,087 — 40,370 Depreciation and amortization 660 — 75,772 9,752 — 86,184 Transaction costs 119 — — — — 119 (Gain) loss on asset sales, net — — (11 ) 541 — 530 Long-lived asset impairment — — 698 879 — 1,577 Total costs and expenses 779 — 212,475 21,865 — 235,119 Other income 214 — — — — 214 Interest expense — (51,883 ) — — — (51,883 ) Early extinguishment of debt — (22,020 ) — — — (22,020 ) Deferred Purchase Price Obligation 54,674 — — — — 54,674 Income (loss) before income taxes and loss from equity method investees 54,109 (73,903 ) 103,333 24,869 — 108,408 Income tax expense (417 ) — — — — (417 ) Loss from equity method investees — — — (3,691 ) — (3,691 ) Equity in earnings of consolidated subsidiaries 50,608 124,511 — — (175,119 ) — Net income $ 104,300 $ 50,608 $ 103,333 $ 21,178 $ (175,119 ) $ 104,300 Condensed Consolidating Statements of Cash Flows. Statements of cash flows for the nine months ended September 30, 2018 and 2017 follow. Nine months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Cash flows from operating activities: Net cash provided by (used in) operating activities $ 3,687 $ (38,590 ) $ 148,237 $ 53,158 $ — $ 166,492 Cash flows from investing activities: Capital expenditures (2,101 ) — (127,362 ) (7,570 ) — (137,033 ) Proceeds from asset sales — — — 496 — 496 Other, net (209 ) — — — — (209 ) Advances to affiliates — (84,148 ) (20,802 ) (46,090 ) 151,040 — Net cash used in investing activities (2,310 ) (84,148 ) (148,164 ) (53,164 ) 151,040 (136,746 ) Cash flows from financing activities: Distributions to common unitholders (135,484 ) — — — — (135,484 ) Distributions to Series A Preferred unitholders (14,250 ) — — — — (14,250 ) Borrowings under Revolving Credit Facility — 202,000 — — — 202,000 Repayments under Revolving Credit Facility — (79,000 ) — — — (79,000 ) Debt issuance costs — (334 ) — — — (334 ) Other, net (2,780 ) — (881 ) (77 ) — (3,738 ) Advances from affiliates 151,040 — — — (151,040 ) — Net cash (used in) provided by financing activities (1,474 ) 122,666 (881 ) (77 ) (151,040 ) (30,806 ) Net change in cash and cash equivalents (97 ) (72 ) (808 ) (83 ) — (1,060 ) Cash and cash equivalents, beginning of period 126 75 1,138 91 — 1,430 Cash and cash equivalents, end of period $ 29 $ 3 $ 330 $ 8 $ — $ 370 Nine months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Cash flows from operating activities: Net cash provided by (used in) operating activities $ 5,707 $ (45,854 ) $ 176,442 $ 60,202 $ — $ 196,497 Cash flows from investing activities: Capital expenditures (995 ) — (64,413 ) (20,798 ) — (86,206 ) Proceeds from asset sales — — — 2,300 — 2,300 Contributions to equity method investees — — — (21,581 ) — (21,581 ) Other, net (579 ) — — — — (579 ) Advances to affiliates 11,768 21,658 (116,254 ) (8,441 ) 91,269 — Net cash provided by (used in) investing activities 10,194 21,658 (180,667 ) (48,520 ) 91,269 (106,066 ) Cash flows from financing activities: Distributions to unitholders (134,066 ) — — — — (134,066 ) Borrowings under Revolving Credit Facility — 177,500 — — — 177,500 Repayments under Revolving Credit Facility — (319,500 ) — — — (319,500 ) Debt issuance costs — (15,891 ) — — — (15,891 ) Payment of redemption and call premiums on senior notes — (17,913 ) — — — (17,913 ) Proceeds from ATM Program issuances, net of costs 17,251 — — — — 17,251 Contribution from General Partner 465 — — — — 465 Issuance of senior notes — 500,000 — — — 500,000 Tender and redemption of senior notes — (300,000 ) — — — (300,000 ) Other, net (2,794 ) — — — — (2,794 ) Advances from affiliates 103,037 — — (11,768 ) (91,269 ) — Net cash (used in) provided by financing activities (16,107 ) 24,196 — (11,768 ) (91,269 ) (94,948 ) Net change in cash and cash equivalents (206 ) — (4,225 ) (86 ) — (4,517 ) Cash and cash equivalents, beginning of period 698 51 5,768 911 — 7,428 Cash and cash equivalents, end of period $ 492 $ 51 $ 1,543 $ 825 $ — $ 2,911

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	19. SUBSEQUENT EVENTS We have evaluated subsequent events for recognition or disclosure in the unaudited condensed consolidated financial statements and no events have occurred that require disclosure, except for the following: In October 2018, we received information from customers on our Utica Shale, Ohio Gathering and Williston Basin segments. The impact of this new information would result in a decrease to the calculation of the undiscounted value of the Deferred Purchase Price Obligation of approximately $16.9 million, from $470.9 million to $454.0 million.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Accounting Pronouncements	Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. We review new pronouncements to determine the impact, if any, on our financial statements. Accounting standards that have or could possibly have a material effect on our financial statements are discussed below. Recently Adopted Accounting Pronouncements . We have recently adopted the following accounting pronouncements: • ASU No. 2014-09 Revenue from Contracts with Customers (“Topic 606”). We adopted Topic 606 with a date of initial application of January 1, 2018. We applied Topic 606 by recognizing the cumulative effect of initially applying Topic 606 as an adjustment to the opening balance of partners’ capital at January 1, 2018. The comparative information has not been adjusted and is reported under the accounting standards in effect for those periods. For contracts where we perform gathering services and earn a per-unit fee which is recognized at a point in time, revenue is recognized over time as the service is performed and results in revenue recognition materially consistent with historical GAAP. In addition, our contracts generally contain forms of variable consideration, which will likely be constrained as the volumes are susceptible to factors outside of our control and influence. As a result of applying the constraint guidance, timing of revenue recognition will be materially consistent with historical GAAP. Prior to the adoption of Topic 606, contributions in aid of construction were recognized as a reduction to our cost basis of property, plant and equipment and facility fees were recognized as revenue when the amounts were billed. Upon adoption of Topic 606, the contributions in aid of construction amounts previously received were capitalized to property, plant and equipment, net of any accumulated depreciation, and will be depreciated over the remaining useful lives. Any future contributions in aid of construction will be recognized as revenue over the remaining term of the respective contract in accordance with Topic 606. Additionally, facility fees will be deferred and recognized over the contract term. There are certain percent-of-proceeds contracts within our Williston Basin reportable segment where we previously recognized revenue for services provided to producers in gathering services and related fees. Such amounts which were previously presented gross in gathering services and related fees are presented net within cost of natural gas and NGLs. This change did not have any impact on our net income (loss), cash flows, or the amount we present as segment adjusted EBITDA. For contracts containing MVC arrangements with banking mechanisms we previously deferred revenue. Under Topic 606, the recognition of revenue was accelerated. This acceleration totaled $16.7 million and is included in the Topic 606 day one adjustment amounts below in deferred revenue. The cumulative effect of the changes made to our consolidated January 1, 2018 balance sheet for the adoption of Topic 606 was as follows: Balance at December 31, 2017 Adjustments Due to Topic 606 Balance at January 1, 2018 (In thousands) Assets Property, plant and equipment, net $ 1,795,129 $ 33,123 $ 1,828,252 Liabilities Deferred revenue, current 4,000 6,088 10,088 Deferred revenue, noncurrent 12,707 22,821 35,528 Partners' Capital (1) 1,084,430 4,214 1,088,644 ________ (1) Includes common limited partner capital and general partner interests. Impact on financial statements The following tables summarize the impact of Topic 606 adoption on our unaudited condensed consolidated financial statements. Unaudited condensed consolidated balance sheet September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Assets Accounts receivable $ 85,458 $ 76,656 $ 8,802 Other noncurrent assets 18,566 12,566 6,000 Property, plant and equipment, net 1,911,630 1,874,388 37,242 Liabilities Deferred revenue, current 11,152 4,071 7,081 Deferred revenue, noncurrent 39,624 10,065 29,559 Partners' Capital (1) 939,293 923,889 15,404 ________ (1) Includes common limited partner capital and general partner interests. Unaudited condensed consolidated statement of operations Three months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 86,427 $ 83,351 $ 3,076 Costs and expenses Cost of natural gas and NGLs 26,879 30,307 (3,428 ) Depreciation and amortization 26,743 26,373 370 Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 260,373 $ 255,546 $ 4,827 Costs and expenses Cost of natural gas and NGLs 71,549 81,468 (9,919 ) Depreciation and amortization 80,204 79,219 985 Unaudited condensed consolidated statement of cash flows Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Cash flows from operating activities: Net income (loss) $ 3,697 $ (10,064 ) $ 13,761 Adjustments to reconcile net loss to net cash provided by operating activities: Depreciation and amortization 79,752 78,767 985 Changes in operating assets and liabilities: Accounts receivable (11,557 ) (2,755 ) (8,802 ) Other, net (7,634 ) (1,634 ) (6,000 ) Deferred revenue, net 5,160 5,104 56 • ASU No. 2017-04 Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"). ASU 2017-04 simplifies the subsequent measurement of goodwill by, among other things, eliminating step two from the goodwill impairment test. ASU 2017-04 is effective for public companies for fiscal years beginning after December 15, 2019 and it specifies the amendments in ASU 2017-04 should be applied on a prospective basis. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We adopted the provisions of ASU 2017-04 effective January 1, 2018. The adoption of this standard had no impact on our consolidated financial statements. Accounting Pronouncements Pending Adoption • ASU No. 2016-02 Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 requires that lessees recognize all leases on the balance sheet, with the exception of short-term leases. A lease liability will be recorded for the obligation of a lessee to make lease payments arising from a lease. A right-of-use asset will be recorded which represents the lessee’s right to use, or to control the use of, a specified asset for a lease term. ASU 2016-02 is effective for public companies for fiscal years beginning after December 15, 2018, and requires the modified retrospective approach for transition. We are currently evaluating the provisions of ASU 2016-02 to determine its impact on our financial statements and related disclosures and will adopt its provisions effective January 1, 2019. We expect to utilize certain practical expedients including (i) not being required to reassess whether any expired or existing contracts are or contain leases; (ii) not being required to reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with Topic 840 will be classified as operating leases, and all existing leases that were classified as capital leases in accordance with Topic 840 will be classified as finance leases); and (iii) not being required to reassess initial direct costs for any existing leases. • ASU No. 2018-01 Leases: Land Easement Practical Expedient for Transition to Topic 842 (“ASU 2018-01”). ASU 2018-01 provides an optional transition practical expedient to not evaluate existing or expired land easements that were not previously accounted for as leases under the current lease guidance in Topic 840. Upon adoption of Topic 842, an entity that elects this practical expedient should evaluate new or modified land easements under Topic 842 beginning at the date the entity adopts Topic 842. We expect to adopt the optional transition practical expedient of ASU 2018-01 effective January 1, 2019. • ASU No. 2018-13 Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 updates the disclosure requirements on fair value measurements including new disclosures for the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 modifies existing disclosures including clarifying the measurement uncertainty disclosure. ASU 2018-13 removes certain existing disclosure requirements including the amount and reasons for transfers between Level 1 and Level 2 fair value measurements and the policy for the timing of transfer between levels. We are currently evaluating the provisions of ASU 2018-13 to determine its impact on our financial statements and related disclosures and will adopt its provisions effective January 1, 2020.
Basis of Presentation	Presentation and Consolidation. We prepare our unaudited condensed consolidated financial statements in accordance with GAAP as established by the FASB. We make estimates and assumptions that affect the reported amounts of assets and liabilities at the balance sheet dates, including fair value measurements, the reported amounts of revenue and expense and the disclosure of contingencies. Although management believes these estimates are reasonable, actual results could differ from its estimates. These unaudited condensed consolidated financial statements have been prepared pursuant to the rules and the regulations of the SEC. Certain information and note disclosures normally included in the annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. We believe that the disclosures made are adequate to make the information not misleading. In the opinion of management, the unaudited condensed consolidated financial statements contain all adjustments, including normal recurring adjustments, which are necessary to fairly present the unaudited condensed consolidated balance sheet as of September 30, 2018, the unaudited condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017 and the unaudited condensed consolidated statements of partners’ capital and cash flows for the nine months ended September 30, 2018 and 2017. The balance sheet at December 31, 2017 included herein was derived from our audited financial statements, but does not include all disclosures required by GAAP. See Notes 2 and 3 for the impact relating to the adoption of the new revenue standard. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto that are included in our annual report on Form 10-K for the year ended December 31, 2017, as filed with the SEC on February 26, 2018 (the "2017 Annual Report"). The results of operations for an interim period are not necessarily indicative of results expected for a full year.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule of Cumulative Effect of Changes made to Balance Sheet for the Adoption of Topic 606	The cumulative effect of the changes made to our consolidated January 1, 2018 balance sheet for the adoption of Topic 606 was as follows: Balance at December 31, 2017 Adjustments Due to Topic 606 Balance at January 1, 2018 (In thousands) Assets Property, plant and equipment, net $ 1,795,129 $ 33,123 $ 1,828,252 Liabilities Deferred revenue, current 4,000 6,088 10,088 Deferred revenue, noncurrent 12,707 22,821 35,528 Partners' Capital (1) 1,084,430 4,214 1,088,644 ________ (1) Includes common limited partner capital and general partner interests.
Summary of Impact of Topic 606 Adoption on Unaudited Condensed Consolidated Financial Statements	The following tables summarize the impact of Topic 606 adoption on our unaudited condensed consolidated financial statements. Unaudited condensed consolidated balance sheet September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Assets Accounts receivable $ 85,458 $ 76,656 $ 8,802 Other noncurrent assets 18,566 12,566 6,000 Property, plant and equipment, net 1,911,630 1,874,388 37,242 Liabilities Deferred revenue, current 11,152 4,071 7,081 Deferred revenue, noncurrent 39,624 10,065 29,559 Partners' Capital (1) 939,293 923,889 15,404 ________ (1) Includes common limited partner capital and general partner interests. Unaudited condensed consolidated statement of operations Three months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 86,427 $ 83,351 $ 3,076 Costs and expenses Cost of natural gas and NGLs 26,879 30,307 (3,428 ) Depreciation and amortization 26,743 26,373 370 Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Revenues Gathering services and related fees $ 260,373 $ 255,546 $ 4,827 Costs and expenses Cost of natural gas and NGLs 71,549 81,468 (9,919 ) Depreciation and amortization 80,204 79,219 985 Unaudited condensed consolidated statement of cash flows Nine months ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase / (Decrease) (In thousands) Cash flows from operating activities: Net income (loss) $ 3,697 $ (10,064 ) $ 13,761 Adjustments to reconcile net loss to net cash provided by operating activities: Depreciation and amortization 79,752 78,767 985 Changes in operating assets and liabilities: Accounts receivable (11,557 ) (2,755 ) (8,802 ) Other, net (7,634 ) (1,634 ) (6,000 ) Deferred revenue, net 5,160 5,104 56

REVENUE (Tables)

REVENUE (Tables)	9 Months Ended
	Sep. 30, 2018
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 2018 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments. We applied the practical expedient in paragraph 606-10-50-14 of Topic 606 for certain arrangements that we consider optional purchases (i.e., there is no enforceable obligation for the customer to make purchases) and those amounts are excluded from the table. 2018 2019 2020 2021 2022 Thereafter (In thousands) Gathering services and related fees $ 84,164 $ 127,743 $ 122,429 $ 102,777 $ 83,648 $ 174,825
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 4. Reportable Segments Three months ended September 30, 2018 Utica Shale Williston Basin Piceance / DJ Basins Barnett Shale Marcellus Shale Total reportable segments All other segments Total (In thousands) Major products/services lines Gathering services and related fees $ 7,974 $ 18,020 $ 36,743 $ 18,318 $ 7,150 $ 88,205 $ (1,778 ) $ 86,427 Natural gas, NGLs and condensate sales — 7,953 3,650 789 — 12,392 21,625 34,017 Other revenues — 3,037 2,072 1,913 — 7,022 13 7,035 Total $ 7,974 $ 29,010 $ 42,465 $ 21,020 $ 7,150 $ 107,619 $ 19,860 $ 127,479 Reportable Segments Nine months ended September 30, 2018 Utica Shale Williston Basin Piceance / DJ Basins Barnett Shale Marcellus Shale Total reportable segments All other segments Total (In thousands) Major products/services lines Gathering services and related fees $ 28,437 $ 58,792 $ 108,207 $ 46,035 $ 23,025 $ 264,496 $ (4,123 ) $ 260,373 Natural gas, NGLs and condensate sales — 23,149 12,650 1,715 — 37,514 54,511 92,025 Other revenues — 8,909 6,187 5,595 — 20,691 (107 ) 20,584 Total $ 28,437 $ 90,850 $ 127,044 $ 53,345 $ 23,025 $ 322,701 $ 50,281 $ 372,982
Schedule of Information about Contract Assets from Contracts with Customers	The following table provides information about contract assets from contracts with customers: September 30, 2018 (In thousands) Contract assets, December 31, 2017 $ — Net impact of Topic 606 day 1 adoption 3,514 Additions 14,906 Transfers out (7,169 ) Contract assets, September 30, 2018 $ 11,251

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule of assets by reportable segment	Assets by reportable segment follow. September 30, 2018 December 31, 2017 (In thousands) Assets: Utica Shale $ 209,105 $ 212,311 Ohio Gathering 660,254 690,485 Williston Basin 529,370 512,860 Piceance/DJ Basins 839,166 798,722 Barnett Shale 380,161 383,306 Marcellus Shale 210,509 217,362 Total reportable segment assets 2,828,565 2,815,046 Corporate and Other 152,375 79,996 Eliminations (2,884 ) (249 ) Total assets $ 2,978,056 $ 2,894,793
Schedule of segment reporting information	Revenues by reportable segment follow. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Revenues (1): Utica Shale $ 7,974 $ 9,727 $ 28,437 $ 28,979 Williston Basin 29,010 27,821 90,850 123,820 Piceance/DJ Basins 42,465 53,875 127,044 122,446 Barnett Shale 21,020 16,694 53,345 55,340 Marcellus Shale 7,150 8,160 23,025 22,429 Total reportable segments revenue 107,619 116,277 322,701 353,014 Corporate and Other 23,636 11,816 57,234 14,964 Eliminations (3,776 ) (3,148 ) (6,953 ) (5,436 ) Total revenues $ 127,479 $ 124,945 $ 372,982 $ 362,542 (1) Excludes revenues earned by Ohio Gathering due to equity method accounting. Depreciation and amortization, including the amortization expense associated with our favorable and unfavorable gas gathering contracts as reported in other revenues, by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Depreciation and amortization (1): Utica Shale $ 1,887 $ 1,818 $ 5,773 $ 5,213 Williston Basin 5,672 8,405 16,903 25,171 Piceance/DJ Basins 12,512 12,199 37,517 36,635 Barnett Shale (2) 3,760 3,735 11,276 11,259 Marcellus Shale 2,273 2,268 6,819 6,794 Total reportable segment depreciation and amortization 26,104 28,425 78,288 85,072 Corporate and Other 488 352 1,464 660 Total depreciation and amortization $ 26,592 $ 28,777 $ 79,752 $ 85,732 (1) Excludes depreciation and amortization recognized by Ohio Gathering due to equity method accounting. (2) Includes the amortization expense associated with our favorable and unfavorable gas gathering contracts as reported in other revenues. Cash paid for capital expenditures by reportable segment follow. Nine months ended September 30, 2018 2017 (In thousands) Cash paid for capital expenditures (1): Utica Shale $ 3,922 $ 21,425 Williston Basin 18,463 13,735 Piceance/DJ Basins 44,166 17,902 Barnett Shale 914 119 Marcellus Shale 557 628 Total reportable segment capital expenditures 68,022 53,809 Corporate and Other 69,011 32,397 Total cash paid for capital expenditures $ 137,033 $ 86,206 (1) Excludes cash paid for capital expenditures by Ohio Gathering due to equity method accounting.
Schedule of counterparties accounting for more than 10% of total revenues	Counterparties accounting for more than 10% of total revenues were as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Percentage of total revenues (1)(2): Counterparty A - Piceance/DJ Basins 11 % 17 % 11 % * Counterparty B - Barnett Shale 12 % * 10 % * Counterparty C - Williston Basin * * * 16 % (1) Includes recognition of revenue that was previously deferred in connection with minimum volume commitments. (2) Excludes revenues earned by Ohio Gathering due to equity method accounting. * Less than 10%
Reconciliation of net income to adjusted EBITDA	Segment adjusted EBITDA by reportable segment follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Reportable segment adjusted EBITDA Utica Shale $ 6,521 $ 8,412 $ 24,459 $ 25,857 Ohio Gathering 10,171 10,522 29,583 29,201 Williston Basin 19,849 16,212 54,849 51,176 Piceance/DJ Basins 29,831 30,008 86,739 86,256 Barnett Shale 10,818 10,838 31,770 35,924 Marcellus Shale 5,550 6,682 18,769 17,775 Total of reportable segments' measures of profit $ 82,740 $ 82,674 $ 246,169 $ 246,189 A reconciliation of income or loss before income taxes and income or loss from equity method investees to total of reportable segments' measures of profit or loss follows. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Reconciliation of income before income taxes and (loss) income from equity method investees to total of reportable segments' measures of profit: Income before income taxes and (loss) income from equity method investees $ 58,589 $ 93,463 $ 7,488 $ 108,408 Add: Corporate and Other 9,324 9,197 28,949 28,725 Interest expense 14,862 17,614 44,821 51,883 Early extinguishment of debt — — — 22,020 Deferred Purchase Price Obligation (37,204 ) (70,499 ) 53,759 (54,674 ) Depreciation and amortization 26,592 28,777 79,752 85,732 Proportional adjusted EBITDA for equity method investees 10,171 10,522 29,583 29,201 Adjustments related to MVC shortfall payments (2,999 ) (10,124 ) (6,541 ) (33,186 ) Adjustments related to capital reimbursement activity (106 ) — 49 — Unit-based and noncash compensation 1,965 1,974 6,188 5,973 Loss (gain) on asset sales, net 6 460 (6 ) 530 Long-lived asset impairment 1,540 1,290 2,127 1,577 Total of reportable segments' measures of profit $ 82,740 $ 82,674 $ 246,169 $ 246,189
Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments	Adjustments related to MVC shortfall payments by reportable segment follow. Three months ended September 30, 2018 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments 2,032 — (5,031 ) (2,999 ) Total adjustments related to MVC shortfall payments $ 2,032 $ — $ (5,031 ) $ (2,999 ) Three months ended September 30, 2017 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments 1,982 (12,200 ) 94 (10,124 ) Total adjustments related to MVC shortfall payments $ 1,982 $ (12,200 ) $ 94 $ (10,124 ) Nine months ended September 30, 2018 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ — $ — $ — $ — Expected MVC shortfall adjustments (1,354 ) (93 ) (5,094 ) (6,541 ) Total adjustments related to MVC shortfall payments $ (1,354 ) $ (93 ) $ (5,094 ) $ (6,541 ) Nine months ended September 30, 2017 Williston Basin Piceance/DJ Basins Barnett Shale Total (In thousands) Adjustments related to MVC shortfall payments: Net change in deferred revenue for MVC shortfall payments $ (37,693 ) $ (1,978 ) $ — $ (39,671 ) Expected MVC shortfall adjustments 5,946 867 (328 ) 6,485 Total adjustments related to MVC shortfall payments $ (31,747 ) $ (1,111 ) $ (328 ) $ (33,186 )

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)	9 Months Ended
	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Schedule of property, plant, and equipment, net	Details on property, plant and equipment follow. September 30, 2018 December 31, 2017 (In thousands) Gathering and processing systems and related equipment $ 2,031,540 $ 1,973,722 Construction in progress 194,472 78,850 Land and line fill 11,747 11,735 Other 42,286 40,262 Total 2,280,045 2,104,569 Less accumulated depreciation 368,415 309,440 Property, plant and equipment, net $ 1,911,630 $ 1,795,129
Schedule of depreciation expense and capitalized interest costs	Depreciation expense and capitalized interest follow. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Depreciation expense $ 18,567 $ 18,837 $ 55,781 $ 55,935 Capitalized interest 2,451 644 5,536 1,562

AMORTIZING INTANGIBLE ASSETS _2

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible assets and liabilities subject to amortization	Details regarding our intangible assets and the unfavorable gas gathering contract (included in other noncurrent liabilities), all of which are subject to amortization, follow. September 30, 2018 Gross carrying amount Accumulated amortization Net (In thousands) Favorable gas gathering contracts $ 24,195 $ (13,517 ) $ 10,678 Contract intangibles 278,448 (137,426 ) 141,022 Rights-of-way 165,445 (35,938 ) 129,507 Total intangible assets $ 468,088 $ (186,881 ) $ 281,207 Unfavorable gas gathering contract $ 10,962 $ (10,692 ) $ 270 December 31, 2017 Gross carrying amount Accumulated amortization Net (In thousands) Favorable gas gathering contracts $ 24,195 $ (12,350 ) $ 11,845 Contract intangibles 278,448 (117,821 ) 160,627 Rights-of-way 159,986 (31,113 ) 128,873 Total intangible assets $ 462,629 $ (161,284 ) $ 301,345 Unfavorable gas gathering contract $ 10,962 $ (9,074 ) $ 1,888
Recognized amortization expense in other revenues and cost and expenses	We recognized amortization expense in other revenues as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Amortization expense – favorable gas gathering contracts $ (389 ) $ (390 ) $ (1,166 ) $ (1,167 ) Amortization expense – unfavorable gas gathering contract 540 540 1,618 1,619 We recognized amortization expense in costs and expenses as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Amortization expense – contract intangibles $ 6,535 $ 8,550 $ 19,605 $ 25,652 Amortization expense – rights-of-way 1,641 1,540 4,818 4,597
Estimated aggregate annual amortization expected to be recognized	The estimated aggregate annual amortization expected to be recognized for the remainder of 2018 and each of the four succeeding fiscal years follows. Intangible assets Unfavorable gas gathering contract (In thousands) 2018 $ 8,562 $ 270 2019 33,321 — 2020 33,145 — 2021 29,453 — 2022 26,386 —

EQUITY METHOD INVESTMENTS (Tabl

EQUITY METHOD INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Equity Method Investments And Joint Ventures [Abstract]
Equity Method Investments	A reconciliation of our Investment in equity method investees, September 30, 2018 $ 660,254 September cash distributions 2,912 Impairment loss 1,837 Basis difference (120,170 ) Investment in equity method investees, net of basis difference, August 31, 2018 $ 544,833 For the three and nine months ended September 30, 2018, there were no contributions to Ohio Gathering. Summarized statements of operations information for OGC and OCC follow (amounts represent 100% of investee financial information). Results include gross asset impairments of $4.6 million and $16.9 million for the three and nine months ending September 30, 2018 and $8.7 million for the three and nine months ending September 30, 2017. Three months ended August 31, 2018 Three months ended August 31, 2017 OGC OCC OGC OCC (In thousands) Total revenues $ 37,180 $ 2,465 $ 35,144 $ 1,814 Total operating expenses 31,751 2,323 25,720 1,877 Net income (loss) 5,429 (5 ) 9,424 (204 ) Nine months ended August 31, 2018 Nine months ended August 31, 2017 OGC OCC OGC OCC (In thousands) Total revenues $ 106,263 $ 7,024 $ 103,302 $ 5,871 Total operating expenses 94,044 6,422 86,046 6,186 Net income (loss) 12,213 116 17,258 (1,396 )

DEFERRED REVENUE (Tables)

DEFERRED REVENUE (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
Rollforward of deferred revenue	A rollforward of current deferred revenue follows. Utica Shale Williston Basin Piceance/DJ Basins Barnett Shale Marcellus Shale Total current (In thousands) Current deferred revenue, December 31, 2017, as reported $ — $ — $ 4,000 $ — $ — $ 4,000 Net impact of Topic 606 day 1 adoption 18 1,017 3,396 1,619 38 6,088 Current deferred revenue, January 1, 2018 18 1,017 7,396 1,619 38 10,088 Additions 14 1,367 16,846 1,236 63 19,526 Less revenue recognized 14 985 16,186 1,214 63 18,462 Current deferred revenue, September 30, 2018 $ 18 $ 1,399 $ 8,056 $ 1,641 $ 38 $ 11,152 A rollforward of noncurrent deferred revenue follows. Utica Shale Williston Basin Piceance/DJ Basins Barnett Shale Marcellus Shale Total noncurrent (In thousands) Noncurrent deferred revenue, December 31, 2017, as reported $ — $ — $ 12,707 $ — $ — $ 12,707 Net impact of Topic 606 day 1 adoption 39 4,215 10,017 8,217 333 22,821 Noncurrent deferred revenue, January 1, 2018 39 4,215 22,724 8,217 333 35,528 Additions — 1,851 9,014 2,323 — 13,188 Less reclassification to current deferred revenue 14 1,296 6,483 1,236 63 9,092 Noncurrent deferred revenue, September 30, 2018 $ 25 $ 4,770 $ 25,255 $ 9,304 $ 270 $ 39,624

DEBT (Tables)

DEBT (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of debt and capital leases	Debt consisted of the following: September 30, 2018 December 31, 2017 (In thousands) Summit Holdings' variable rate senior secured Revolving Credit Facility (4.50% at September 30, 2018 and 4.07% at December 31, 2017) due May 2022 $ 384,000 $ 261,000 Summit Holdings' 5.5% senior unsecured notes due August 2022 300,000 300,000 Less unamortized debt issuance costs (1) (2,530 ) (2,910 ) Summit Holdings' 5.75% senior unsecured notes due April 2025 500,000 500,000 Less unamortized debt issuance costs (1) (6,157 ) (6,898 ) Total long-term debt $ 1,175,313 $ 1,051,192 (1) Issuance costs are being amortized over the life of the notes.

FINANCIAL INSTRUMENTS (Tables)

FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	A rollforward of our Level 3 liability measured at fair value on a recurring basis follows (in thousands). Level 3 liability, January 1, 2018 $ 362,959 Change in fair value 53,759 Level 3 liability, September 30, 2018 $ 416,718
Summary of the estimated fair value of debt instruments	A summary of the estimated fair value of our debt financial instruments follows. September 30, 2018 December 31, 2017 Carrying value Estimated fair value (Level 2) Carrying value Estimated fair value (Level 2) (In thousands) Summit Holdings 5.5% Senior Notes ($300.0 million principal) $ 297,470 $ 300,000 $ 297,090 $ 301,750 Summit Holdings 5.75% Senior Notes ($500.0 million principal) 493,843 481,250 493,102 501,667

PARTNERS' CAPITAL (Tables)

PARTNERS' CAPITAL (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Schedule of partner units activity	A rollforward of the number of common limited partner and General Partner units follows. Limited partners Series A Preferred Units Common General Partner Units, January 1, 2018 300,000 73,085,996 1,490,999 Net units issued under the SMLP LTIP — 269,779 — Units, September 30, 2018 300,000 73,355,775 1,490,999
Details of cash distributions	We paid the following per-unit distributions during the three and nine months ended September 30: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Per-unit distributions to unitholders $ 0.575 $ 0.575 $ 1.725 $ 1.725 Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) IDR payments $ 2,136 $ 2,127 $ 6,400 $ 6,333

EARNINGS PER UNIT (Tables)

EARNINGS PER UNIT (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 2017 2018 2017 (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 $ 54,151 $ 89,547 $ (2,948 ) $ 95,576 Less net income attributable to Series A Preferred Units 7,125 — 21,375 — Net income (loss) attributable to common limited partners $ 47,026 $ 89,547 $ (24,323 ) $ 95,576 Denominator for basic and diluted EPU: Weighted-average common units outstanding – basic 73,356 73,059 73,283 72,583 Effect of nonvested phantom units 400 374 — 318 Weighted-average common units outstanding – diluted 73,756 73,433 73,283 72,901 Earnings (loss) per limited partner unit: Common unit – basic $ 0.64 $ 1.23 $ (0.33 ) $ 1.32 Common unit – diluted $ 0.64 $ 1.22 $ (0.33 ) $ 1.31 Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU 1 — 2 55

RELATED-PARTY TRANSACTIONS (Tab

RELATED-PARTY TRANSACTIONS (Tables)	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Schedule of related party transactions	Expenses incurred by the General Partner and reimbursed by us under our Partnership Agreement were as follows: Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Operation and maintenance expense $ 7,161 $ 6,792 $ 21,898 $ 20,404 General and administrative expense 7,220 6,840 22,818 23,030

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of total rent expense related to operating leases	Rent expense related to operating leases, including rent expense incurred on our behalf and allocated to us, was as follows Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (In thousands) Rent expense $ 957 $ 1,009 $ 2,935 $ 2,811
Schedule of accrued environmental remediation	A rollforward of the aggregate accrued environmental remediation liabilities follows. Total (In thousands) Accrued environmental remediation, January 1, 2018 $ 5,344 Payments made (3,060 ) Additional accruals 1,600 Accrued environmental remediation, September 30, 2018 $ 3,884

CONDENSED CONSOLIDATING FINAN_2

CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Condensed Balance Sheet	Balance sheets as of September 30, 2018 and December 31, 2017 follow. September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Assets Cash and cash equivalents $ 29 $ 3 $ 330 $ 8 $ — $ 370 Accounts receivable 22 — 74,766 10,670 — 85,458 Other current assets 843 — 2,922 595 — 4,360 Due from affiliate — — 513,867 68,121 (581,988 ) — Total current assets 894 3 591,885 79,394 (581,988 ) 90,188 Property, plant and equipment, net 5,134 — 1,563,950 342,546 — 1,911,630 Intangible assets, net — — 255,317 25,890 — 281,207 Goodwill — — 16,211 — — 16,211 Investment in equity method investees — — — 660,254 — 660,254 Other noncurrent assets 3,320 9,184 6,062 — — 18,566 Investment in subsidiaries 2,082,686 3,432,198 — — (5,514,884 ) — Total assets $ 2,092,034 $ 3,441,385 $ 2,433,425 $ 1,108,084 $ (6,096,872 ) $ 2,978,056 Liabilities and Partners' Capital Trade accounts payable $ 219 $ — $ 18,523 $ 3,827 $ — $ 22,569 Accrued expenses 725 — 16,051 1,571 — 18,347 Due to affiliate 413,900 168,101 — — (581,988 ) 13 Deferred revenue — — 10,716 436 — 11,152 Ad valorem taxes payable 14 — 7,802 407 — 8,223 Accrued interest — 15,285 — — — 15,285 Accrued environmental remediation — — — 2,702 — 2,702 Other current liabilities 5,386 — 4,488 514 — 10,388 Total current liabilities 420,244 183,386 57,580 9,457 (581,988 ) 88,679 Long-term debt — 1,175,313 — — — 1,175,313 Deferred Purchase Price Obligation 416,718 — — — — 416,718 Noncurrent deferred revenue — — 37,802 1,822 — 39,624 Noncurrent accrued environmental remediation — — — 1,182 — 1,182 Other noncurrent liabilities 4,057 — 1,437 31 — 5,525 Total liabilities 841,019 1,358,699 96,819 12,492 (581,988 ) 1,727,041 Total partners' capital 1,251,015 2,082,686 2,336,606 1,095,592 (5,514,884 ) 1,251,015 Total liabilities and partners' capital $ 2,092,034 $ 3,441,385 $ 2,433,425 $ 1,108,084 $ (6,096,872 ) $ 2,978,056 December 31, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Assets Cash and cash equivalents $ 126 $ 75 $ 1,138 $ 91 $ — $ 1,430 Accounts receivable 22 — 65,842 6,437 — 72,301 Other current assets 1,188 — 2,697 442 — 4,327 Due from affiliate — — 493,067 22,030 (515,097 ) — Total current assets 1,336 75 562,744 29,000 (515,097 ) 78,058 Property, plant and equipment, net 4,206 — 1,442,333 348,590 — 1,795,129 Intangible assets, net — — 278,958 22,387 — 301,345 Goodwill — — 16,211 — — 16,211 Investment in equity method investees — — — 690,485 — 690,485 Other noncurrent assets 2,547 10,913 105 — — 13,565 Investment in subsidiaries 2,019,700 3,324,464 — — (5,344,164 ) — Total assets $ 2,027,789 $ 3,335,452 $ 2,300,351 $ 1,090,462 $ (5,859,261 ) $ 2,894,793 Liabilities and Partners' Capital Trade accounts payable $ 209 $ — $ 11,283 $ 4,883 $ — $ 16,375 Accrued expenses 928 — 10,592 979 — 12,499 Due to affiliate 263,935 252,250 — — (515,097 ) 1,088 Deferred revenue — — 4,000 — — 4,000 Ad valorem taxes payable — — 7,809 520 — 8,329 Accrued interest — 12,310 — — — 12,310 Accrued environmental remediation — — — 3,130 — 3,130 Other current liabilities 6,395 — 4,385 478 — 11,258 Total current liabilities 271,467 264,560 38,069 9,990 (515,097 ) 68,989 Long-term debt — 1,051,192 — — — 1,051,192 Deferred Purchase Price Obligation 362,959 — — — — 362,959 Deferred revenue — — 12,707 — — 12,707 Noncurrent accrued environmental remediation — — — 2,214 — 2,214 Other noncurrent liabilities 3,694 — 3,293 76 — 7,063 Total liabilities 638,120 1,315,752 54,069 12,280 (515,097 ) 1,505,124 Total partners' capital 1,389,669 2,019,700 2,246,282 1,078,182 (5,344,164 ) 1,389,669 Total liabilities and partners' capital $ 2,027,789 $ 3,335,452 $ 2,300,351 $ 1,090,462 $ (5,859,261 ) $ 2,894,793
Condensed Statement of Operations	Statements of operations for the three and nine months ended September 30, 2018 and 2017 follow. Three months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 73,014 $ 13,413 $ — $ 86,427 Natural gas, NGLs and condensate sales — — 34,017 — — 34,017 Other revenues — — 6,806 229 — 7,035 Total revenues — — 113,837 13,642 — 127,479 Costs and expenses: Cost of natural gas and NGLs — — 26,879 — — 26,879 Operation and maintenance — — 21,721 2,661 — 24,382 General and administrative — — 10,535 1,205 — 11,740 Depreciation and amortization 429 — 22,863 3,451 — 26,743 Loss on asset sales, net — — 1 5 — 6 Long-lived asset impairment — — 275 1,265 — 1,540 Total costs and expenses 429 — 82,274 8,587 — 91,290 Other income 58 — — — — 58 Interest expense — (14,862 ) — — — (14,862 ) Deferred Purchase Price Obligation 37,204 — — — — 37,204 Income (loss) before income taxes and loss from equity method investees 36,833 (14,862 ) 31,563 5,055 — 58,589 Income tax benefit 35 — — — — 35 Loss from equity method investees — — — (1,169 ) — (1,169 ) Equity in earnings of consolidated subsidiaries 20,587 35,449 — — (56,036 ) — Net income $ 57,455 $ 20,587 $ 31,563 $ 3,886 $ (56,036 ) $ 57,455 Three months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 82,152 $ 13,918 $ — $ 96,070 Natural gas, NGLs and condensate sales — — 22,940 — — 22,940 Other revenues — — 5,877 58 — 5,935 Total revenues — — 110,969 13,976 — 124,945 Costs and expenses: Cost of natural gas and NGLs — — 18,177 — — 18,177 Operation and maintenance — — 20,217 2,086 — 22,303 General and administrative — — 11,919 1,370 — 13,289 Depreciation and amortization 352 — 25,247 3,328 — 28,927 Transaction costs — — — — — — (Gain) loss on asset sales, net — — (82 ) 542 — 460 Long-lived asset impairment — — 696 594 — 1,290 Total costs and expenses 352 — 76,174 7,920 — 84,446 Other income 79 — — — — 79 Interest expense — (17,614 ) — — — (17,614 ) Deferred Purchase Price Obligation 70,499 — — — — 70,499 Income (loss) before income taxes and income from equity method investees 70,226 (17,614 ) 34,795 6,056 — 93,463 Income tax expense (176 ) — — — — (176 ) Income from equity method investees — — — 350 — 350 Equity in earnings of consolidated subsidiaries 23,587 41,201 — — (64,788 ) — Net income $ 93,637 $ 23,587 $ 34,795 $ 6,406 $ (64,788 ) $ 93,637 Nine months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 216,371 $ 44,002 $ — $ 260,373 Natural gas, NGLs and condensate sales — — 92,025 — — 92,025 Other revenues — — 20,042 542 — 20,584 Total revenues — — 328,438 44,544 — 372,982 Costs and expenses: Cost of natural gas and NGLs — — 71,549 — — 71,549 Operation and maintenance — — 66,095 7,357 — 73,452 General and administrative — — 34,786 4,880 — 39,666 Depreciation and amortization 1,305 — 68,500 10,399 — 80,204 (Gain) loss on asset sales, net — — (74 ) 68 — (6 ) Long-lived asset impairment — — 862 1,265 — 2,127 Total costs and expenses 1,305 — 241,718 23,969 — 266,992 Other income 78 — — — — 78 Interest expense — (44,821 ) — — — (44,821 ) Deferred Purchase Price Obligation (53,759 ) — — — — (53,759 ) (Loss) income before income taxes and loss from equity method investees (54,986 ) (44,821 ) 86,720 20,575 — 7,488 Income tax expense (88 ) — — — — (88 ) Loss from equity method investees — — — (3,703 ) — (3,703 ) Equity in earnings of consolidated subsidiaries 58,771 103,592 — — (162,363 ) — Net income $ 3,697 $ 58,771 $ 86,720 $ 16,872 $ (162,363 ) $ 3,697 Nine months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Revenues: Gathering services and related fees $ — $ — $ 252,344 $ 46,540 $ — $ 298,884 Natural gas, NGLs and condensate sales — — 44,655 — — 44,655 Other revenues — — 18,809 194 — 19,003 Total revenues — — 315,808 46,734 — 362,542 Costs and expenses: Cost of natural gas and NGLs — — 36,328 — — 36,328 Operation and maintenance — — 64,405 5,606 — 70,011 General and administrative — — 35,283 5,087 — 40,370 Depreciation and amortization 660 — 75,772 9,752 — 86,184 Transaction costs 119 — — — — 119 (Gain) loss on asset sales, net — — (11 ) 541 — 530 Long-lived asset impairment — — 698 879 — 1,577 Total costs and expenses 779 — 212,475 21,865 — 235,119 Other income 214 — — — — 214 Interest expense — (51,883 ) — — — (51,883 ) Early extinguishment of debt — (22,020 ) — — — (22,020 ) Deferred Purchase Price Obligation 54,674 — — — — 54,674 Income (loss) before income taxes and loss from equity method investees 54,109 (73,903 ) 103,333 24,869 — 108,408 Income tax expense (417 ) — — — — (417 ) Loss from equity method investees — — — (3,691 ) — (3,691 ) Equity in earnings of consolidated subsidiaries 50,608 124,511 — — (175,119 ) — Net income $ 104,300 $ 50,608 $ 103,333 $ 21,178 $ (175,119 ) $ 104,300
Condensed Cash Flow Statement	Statements of cash flows for the nine months ended September 30, 2018 and 2017 follow. Nine months ended September 30, 2018 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Cash flows from operating activities: Net cash provided by (used in) operating activities $ 3,687 $ (38,590 ) $ 148,237 $ 53,158 $ — $ 166,492 Cash flows from investing activities: Capital expenditures (2,101 ) — (127,362 ) (7,570 ) — (137,033 ) Proceeds from asset sales — — — 496 — 496 Other, net (209 ) — — — — (209 ) Advances to affiliates — (84,148 ) (20,802 ) (46,090 ) 151,040 — Net cash used in investing activities (2,310 ) (84,148 ) (148,164 ) (53,164 ) 151,040 (136,746 ) Cash flows from financing activities: Distributions to common unitholders (135,484 ) — — — — (135,484 ) Distributions to Series A Preferred unitholders (14,250 ) — — — — (14,250 ) Borrowings under Revolving Credit Facility — 202,000 — — — 202,000 Repayments under Revolving Credit Facility — (79,000 ) — — — (79,000 ) Debt issuance costs — (334 ) — — — (334 ) Other, net (2,780 ) — (881 ) (77 ) — (3,738 ) Advances from affiliates 151,040 — — — (151,040 ) — Net cash (used in) provided by financing activities (1,474 ) 122,666 (881 ) (77 ) (151,040 ) (30,806 ) Net change in cash and cash equivalents (97 ) (72 ) (808 ) (83 ) — (1,060 ) Cash and cash equivalents, beginning of period 126 75 1,138 91 — 1,430 Cash and cash equivalents, end of period $ 29 $ 3 $ 330 $ 8 $ — $ 370 Nine months ended September 30, 2017 SMLP Co-Issuers Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating adjustments Total (In thousands) Cash flows from operating activities: Net cash provided by (used in) operating activities $ 5,707 $ (45,854 ) $ 176,442 $ 60,202 $ — $ 196,497 Cash flows from investing activities: Capital expenditures (995 ) — (64,413 ) (20,798 ) — (86,206 ) Proceeds from asset sales — — — 2,300 — 2,300 Contributions to equity method investees — — — (21,581 ) — (21,581 ) Other, net (579 ) — — — — (579 ) Advances to affiliates 11,768 21,658 (116,254 ) (8,441 ) 91,269 — Net cash provided by (used in) investing activities 10,194 21,658 (180,667 ) (48,520 ) 91,269 (106,066 ) Cash flows from financing activities: Distributions to unitholders (134,066 ) — — — — (134,066 ) Borrowings under Revolving Credit Facility — 177,500 — — — 177,500 Repayments under Revolving Credit Facility — (319,500 ) — — — (319,500 ) Debt issuance costs — (15,891 ) — — — (15,891 ) Payment of redemption and call premiums on senior notes — (17,913 ) — — — (17,913 ) Proceeds from ATM Program issuances, net of costs 17,251 — — — — 17,251 Contribution from General Partner 465 — — — — 465 Issuance of senior notes — 500,000 — — — 500,000 Tender and redemption of senior notes — (300,000 ) — — — (300,000 ) Other, net (2,794 ) — — — — (2,794 ) Advances from affiliates 103,037 — — (11,768 ) (91,269 ) — Net cash (used in) provided by financing activities (16,107 ) 24,196 — (11,768 ) (91,269 ) (94,948 ) Net change in cash and cash equivalents (206 ) — (4,225 ) (86 ) — (4,517 ) Cash and cash equivalents, beginning of period 698 51 5,768 911 — 7,428 Cash and cash equivalents, end of period $ 492 $ 51 $ 1,543 $ 825 $ — $ 2,911

ORGANIZATION, BUSINESS OPERAT_2

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - shares	1 Months Ended	9 Months Ended
	Feb. 29, 2016	Sep. 30, 2018	Dec. 31, 2017	Jun. 30, 2016
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		73,355,775	73,085,996
Summit Midstream Niobrara, LLC | Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
Cost method ownership interest			1.00%
SMP Holdings | Contributed Entities
Organization And Business Operations [Line Items]
Percent of issued and outstanding membership interest	100.00%
SMP Holdings | OGC
Organization And Business Operations [Line Items]
Percentage of ownership interest	40.00%
Subsidiary of Summit Investments
Organization And Business Operations [Line Items]
Ownership interest				1.00%
Grand River Gathering, LLC
Organization And Business Operations [Line Items]
Percentage of ownership interest			100.00%
Common units | SMP Holdings
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		25,854,581
Common units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		5,915,827
General Partner
Organization And Business Operations [Line Items]
General partner interest		2.00%
General Partner | Summit Investments | Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner interest		2.00%

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Acceleration totaled, recognition of revenue	$ 16.7

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cumulative Effect of Changes made to Balance Sheet for the Adoption of Topic 606 (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Property, plant and equipment, net	$ 1,911,630	$ 1,828,252	$ 1,795,129
Liabilities
Deferred revenue	11,152	10,088	4,000
Deferred revenue, noncurrent	39,624	35,528	12,707
Partners' Capital	939,293	1,088,644
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Property, plant and equipment, net	1,874,388		1,795,129
Liabilities
Deferred revenue	4,071		4,000
Deferred revenue, noncurrent	10,065		12,707
Partners' Capital	923,889		$ 1,084,430
Accounting Standard Update 2014-09 | Adjustments Due to Topic 606
Assets
Property, plant and equipment, net	37,242	33,123
Liabilities
Deferred revenue	7,081	6,088
Deferred revenue, noncurrent	29,559	22,821
Partners' Capital	$ 15,404	$ 4,214

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Impact of Topic 606 Adoption on Unaudited Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 85,458
Other noncurrent assets	18,566		$ 13,565
Property, plant and equipment, net	1,911,630	$ 1,828,252	1,795,129
Liabilities
Deferred revenue	11,152	10,088	4,000
Deferred revenue, noncurrent	39,624	35,528	12,707
Partners' Capital	939,293	1,088,644
Balances Without Adoption of Topic 606
Assets
Accounts receivable	76,656
Other noncurrent assets	12,566
Property, plant and equipment, net	1,874,388		1,795,129
Liabilities
Deferred revenue	4,071		4,000
Deferred revenue, noncurrent	10,065		12,707
Partners' Capital	923,889		$ 1,084,430
Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Assets
Accounts receivable	8,802
Other noncurrent assets	6,000
Property, plant and equipment, net	37,242	33,123
Liabilities
Deferred revenue	7,081	6,088
Deferred revenue, noncurrent	29,559	22,821
Partners' Capital	$ 15,404	$ 4,214

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Impact of Topic 606 Adoption on Unaudited Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Gathering services and related fees	$ 127,479	$ 124,945	$ 372,982	$ 362,542
Costs and expenses:
Cost of natural gas and NGLs	$ 26,879	$ 18,177	$ 71,549	$ 36,328
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Depreciation and amortization	$ 26,743	$ 28,927	$ 80,204	$ 86,184
Balances Without Adoption of Topic 606
Costs and expenses:
Cost of natural gas and NGLs	$ 30,307		$ 81,468
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember		us-gaap:OilAndGasPurchasedMember
Depreciation and amortization	$ 26,373		$ 79,219
Gathering Services and Related Fees
Revenues:
Gathering services and related fees	86,427	$ 96,070	260,373	$ 298,884
Gathering Services and Related Fees | Balances Without Adoption of Topic 606
Revenues:
Gathering services and related fees	83,351		255,546
Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Costs and expenses:
Cost of natural gas and NGLs	$ (3,428)		$ (9,919)
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember		us-gaap:OilAndGasPurchasedMember
Depreciation and amortization	$ 370		$ 985
Accounting Standard Update 2014-09 | Gathering Services and Related Fees | Effect of Change Increase / (Decrease)
Revenues:
Gathering services and related fees	$ 3,076		$ 4,827

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Impact of Topic 606 Adoption on Unaudited Condensed Consolidated Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income (loss)	$ 57,455	$ 93,637	$ 3,697	$ 104,300
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	$ 26,592	$ 28,777	79,752	85,732
Changes in operating assets and liabilities:
Accounts receivable			(11,557)	36,097
Other, net			(7,634)	(2,689)
Deferred revenue, net			5,160	$ (39,671)
Balances Without Adoption of Topic 606
Cash flows from operating activities:
Net income (loss)			(10,064)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization			78,767
Changes in operating assets and liabilities:
Accounts receivable			(2,755)
Other, net			(1,634)
Deferred revenue, net			5,104
Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Cash flows from operating activities:
Net income (loss)			13,761
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization			985
Changes in operating assets and liabilities:
Accounts receivable			(8,802)
Other, net			(6,000)
Deferred revenue, net			$ 56

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Revenue From Contract With Customer [Line Items]
Revenue, performance obligation, description of payment terms		Our services are typically billed on a monthly basis and we do not offer extended payment terms. We do not have contracts with financing components.
Receivables with customers	$ 70,800	$ 70,800
Contract assets included in accounts receivable	11,251	11,251	$ 0
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	2,800	7,800
Other Noncurrent Assets
Revenue From Contract With Customer [Line Items]
Long-term contract assets included in other noncurrent assets	$ 6,000	$ 6,000
Maximum
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	25 years	25 years

REVENUE - Schedule of Estimated

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) $ in Thousands	Sep. 30, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01
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, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, 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, 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, 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	21 years
Gathering Services and Related Fees | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 84,164
Gathering Services and Related Fees | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation	127,743
Gathering Services and Related Fees | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation	122,429
Gathering Services and Related Fees | 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	102,777
Gathering Services and Related Fees | 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	83,648
Gathering Services and Related Fees | 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	$ 174,825

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenues	$ 127,479	$ 124,945	$ 372,982	$ 362,542
All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	19,860		50,281
Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	107,619	116,277	322,701	353,014
Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,974	9,727	28,437	28,979
Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	29,010	27,821	90,850	123,820
Reportable Segments | Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Total revenues	42,465	53,875	127,044	122,446
Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	21,020	16,694	53,345	55,340
Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,150	$ 8,160	23,025	$ 22,429
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Total revenues	86,427		260,373
Gathering Services and Related Fees | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	(1,778)		(4,123)
Gathering Services and Related Fees | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	88,205		264,496
Gathering Services and Related Fees | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,974		28,437
Gathering Services and Related Fees | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	18,020		58,792
Gathering Services and Related Fees | Reportable Segments | Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Total revenues	36,743		108,207
Gathering Services and Related Fees | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	18,318		46,035
Gathering Services and Related Fees | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	7,150		23,025
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Total revenues	34,017		92,025
Natural Gas, NGLs and Condensate Sales | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	21,625		54,511
Natural Gas, NGLs and Condensate Sales | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	12,392		37,514
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0		0
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	7,953		23,149
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Total revenues	3,650		12,650
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	789		1,715
Natural Gas, NGLs and Condensate Sales | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0		0
Other Revenues
Disaggregation Of Revenue [Line Items]
Total revenues	7,035		20,584
Other Revenues | All Other Segments
Disaggregation Of Revenue [Line Items]
Total revenues	13		(107)
Other Revenues | Reportable Segments
Disaggregation Of Revenue [Line Items]
Total revenues	7,022		20,691
Other Revenues | Reportable Segments | Utica Shale
Disaggregation Of Revenue [Line Items]
Total revenues	0		0
Other Revenues | Reportable Segments | Williston Basin
Disaggregation Of Revenue [Line Items]
Total revenues	3,037		8,909
Other Revenues | Reportable Segments | Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Total revenues	2,072		6,187
Other Revenues | Reportable Segments | Barnett Shale
Disaggregation Of Revenue [Line Items]
Total revenues	1,913		5,595
Other Revenues | Reportable Segments | Marcellus Shale
Disaggregation Of Revenue [Line Items]
Total revenues	$ 0		$ 0

REVENUE - Schedule of Informati

REVENUE - Schedule of Information about Contract Assets from Contracts with Customers (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Contract With Customer Asset And Liability [Abstract]
Contract assets, December 31, 2017	$ 0
Net impact of Topic 606 day 1 adoption	3,514
Additions	14,906
Transfers out	(7,169)
Contract assets, September 30, 2018	$ 11,251

SEGMENT INFORMATION - Assets, R

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 2,978,056		$ 2,978,056		$ 2,894,793
Revenues	127,479	$ 124,945	372,982	$ 362,542
Depreciation and amortization	26,592	28,777	79,752	85,732
Capital expenditures			137,033	86,206
Corporate
Segment Reporting Information [Line Items]
Capital expenditures			2,100
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,828,565		2,828,565		2,815,046
Revenues	107,619	116,277	322,701	353,014
Depreciation and amortization	26,104	28,425	78,288	85,072
Capital expenditures			68,022	53,809
Reportable Segments | Utica Shale
Segment Reporting Information [Line Items]
Assets	209,105		209,105		212,311
Revenues	7,974	9,727	28,437	28,979
Depreciation and amortization	1,887	1,818	5,773	5,213
Capital expenditures			3,922	21,425
Reportable Segments | Ohio Gathering
Segment Reporting Information [Line Items]
Assets	660,254		660,254		690,485
Reportable Segments | Williston Basin
Segment Reporting Information [Line Items]
Assets	529,370		529,370		512,860
Revenues	29,010	27,821	90,850	123,820
Depreciation and amortization	5,672	8,405	16,903	25,171
Capital expenditures			18,463	13,735
Reportable Segments | Piceance/DJ Basins
Segment Reporting Information [Line Items]
Assets	839,166		839,166		798,722
Revenues	42,465	53,875	127,044	122,446
Depreciation and amortization	12,512	12,199	37,517	36,635
Capital expenditures			44,166	17,902
Reportable Segments | Barnett Shale
Segment Reporting Information [Line Items]
Assets	380,161		380,161		383,306
Revenues	21,020	16,694	53,345	55,340
Depreciation and amortization	3,760	3,735	11,276	11,259
Capital expenditures			914	119
Reportable Segments | Marcellus Shale
Segment Reporting Information [Line Items]
Assets	210,509		210,509		217,362
Revenues	7,150	8,160	23,025	22,429
Depreciation and amortization	2,273	2,268	6,819	6,794
Capital expenditures			557	628
Corporate and Other
Segment Reporting Information [Line Items]
Assets	152,375		152,375		79,996
Revenues	23,636	11,816	57,234	14,964
Depreciation and amortization	488	352	1,464	660
Capital expenditures			69,011	32,397
Eliminations
Segment Reporting Information [Line Items]
Assets	(2,884)		(2,884)		$ (249)
Revenues	$ (3,776)	$ (3,148)	$ (6,953)	$ (5,436)

SEGMENT INFORMATION - Concentra

SEGMENT INFORMATION - Concentration Risk (Details) - Revenue - Customer concentration	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Counterparty A - Piceance/DJ Basins
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	17.00%	11.00%	0.00%
Counterparty B - Barnett Shale
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	0.00%	10.00%	0.00%
Counterparty C - Williston Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	0.00%	0.00%	0.00%	16.00%

SEGMENT INFORMATION - Adjusted

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 82,740	$ 82,674	$ 246,169	$ 246,189
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,521	8,412	24,459	25,857
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,171	10,522	29,583	29,201
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	19,849	16,212	54,849	51,176
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Adjusted EBITDA	29,831	30,008	86,739	86,256
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,818	10,838	31,770	35,924
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 5,550	$ 6,682	$ 18,769	$ 17,775

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Income before income taxes and (loss) income from equity method investees	$ 58,589,000	$ 93,463,000	$ 7,488,000	$ 108,408,000
Add:
Corporate and Other	9,324,000	9,197,000	28,949,000	28,725,000
Interest expense	14,862,000	17,614,000	44,821,000	51,883,000
Early extinguishment of debt	0	0	0	22,020,000
Deferred Purchase Price Obligation	(37,204,000)	(70,499,000)	53,759,000	(54,674,000)
Depreciation and amortization	26,592,000	28,777,000	79,752,000	85,732,000
Proportional adjusted EBITDA for equity method investees	10,171,000	10,522,000	29,583,000	29,201,000
Adjustments related to MVC shortfall payments	(2,999,000)	(10,124,000)	(6,541,000)	(33,186,000)
Adjustments related to capital reimbursement activity	(106,000)	0	49,000	0
Unit-based and noncash compensation	1,965,000	1,974,000	6,188,000	5,973,000
Loss (gain) on asset sales, net	6,000	460,000	(6,000)	530,000
Long-lived asset impairment	1,540,000	1,290,000	2,127,000	1,577,000
Total of reportable segments' measures of profit	$ 82,740,000	$ 82,674,000	$ 246,169,000	$ 246,189,000

SEGMENT INFORMATION - Schedule

SEGMENT INFORMATION - Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments	$ 0	$ 0	$ 0	$ (39,671,000)
Expected MVC shortfall adjustments	(2,999,000)	(10,124,000)	(6,541,000)	6,485,000
Total adjustments related to MVC shortfall payments	(2,999,000)	(10,124,000)	(6,541,000)	(33,186,000)
Williston Basin
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments	0	0	0	(37,693,000)
Expected MVC shortfall adjustments	2,032,000	1,982,000	(1,354,000)	5,946,000
Total adjustments related to MVC shortfall payments	2,032,000	1,982,000	(1,354,000)	(31,747,000)
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments	0	0	0	(1,978,000)
Expected MVC shortfall adjustments	0	(12,200,000)	(93,000)	867,000
Total adjustments related to MVC shortfall payments	0	(12,200,000)	(93,000)	(1,111,000)
Barnett Shale
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments	0	0	0	0
Expected MVC shortfall adjustments	(5,031,000)	94,000	(5,094,000)	(328,000)
Total adjustments related to MVC shortfall payments	$ (5,031,000)	$ 94,000	$ (5,094,000)	$ (328,000)

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,280,045		$ 2,104,569
Less accumulated depreciation	368,415		309,440
Property, plant and equipment, net	1,911,630	$ 1,828,252	1,795,129
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,031,540		1,973,722
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	194,472		78,850
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,747		11,735
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 42,286		$ 40,262

PROPERTY, PLANT, AND EQUIPMEN_4

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 18,567	$ 18,837	$ 55,781	$ 55,935
Capitalized interest	$ 2,451	$ 644	$ 5,536	$ 1,562

AMORTIZING INTANGIBLE ASSETS _3

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT - Intangible Assets and Liabilities Subject to Amortization (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 468,088	$ 462,629
Accumulated amortization	(186,881)	(161,284)
Net	281,207	301,345
Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24,195	24,195
Accumulated amortization	(13,517)	(12,350)
Net	10,678	11,845
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	278,448	278,448
Accumulated amortization	(137,426)	(117,821)
Net	141,022	160,627
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	165,445	159,986
Accumulated amortization	(35,938)	(31,113)
Net	129,507	128,873
Unfavorable Gas Gathering Contract
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	10,962	10,962
Accumulated amortization	(10,692)	(9,074)
Net	$ 270	$ 1,888

AMORTIZING INTANGIBLE ASSETS _4

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Revenue | Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (389)	$ (390)	$ (1,166)	$ (1,167)
Other Revenue | Unfavorable Gas Gathering Contract
Finite-Lived Intangible Assets [Line Items]
Amortization expense	540	540	1,618	1,619
Costs And Expenses | Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,535	8,550	19,605	25,652
Costs And Expenses | Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,641	$ 1,540	$ 4,818	$ 4,597

AMORTIZING INTANGIBLE ASSETS _5

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT - Estimated Aggregate Annual Amortization Expected to be Recognized (Details) $ in Thousands	Sep. 30, 2018USD ($)
Intangible assets
2,018	$ 8,562
2,019	33,321
2,020	33,145
2,021	29,453
2,022	26,386
Unfavorable gas gathering contract
2,018	270
2,019	0
2,020	0
2,021	0
2,022	$ 0

GOODWILL - Narrative (Details)

GOODWILL - Narrative (Details)	9 Months Ended
	Sep. 30, 2018USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

EQUITY METHOD INVESTMENTS - Nar

EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Equity Method Investments [Line Items]
Impairment loss		$ 1,169,000	$ (350,000)	$ 3,703,000	$ 3,691,000
Contributions to acquire equity method investments				0	21,581,000
OGC
Schedule Of Equity Method Investments [Line Items]
Contributions to acquire equity method investments		$ 0		$ 0
OGC | Principal Owner
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest	40.00%	40.00%		40.00%
OGC | Summit Midstream Partners, LLC
Schedule Of Equity Method Investments [Line Items]
Impairment loss	$ 1,837,000
OGC and OCC
Schedule Of Equity Method Investments [Line Items]
Asset impairment		$ 4,600,000	$ 8,700,000	$ 16,900,000	$ 8,700,000

EQUITY METHOD INVESTMENTS - Rol

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity Method Investment [Roll Forward]
Investment in equity method investees, September 30, 2018	$ 660,254	$ 660,254		$ 660,254
September cash distributions				26,528	$ 28,715
Impairment loss		1,169	$ (350)	3,703	$ 3,691
Investment in equity method investees, net of basis difference, August 31, 2018				690,485
OGC | Summit Midstream Partners, LLC
Equity Method Investment [Roll Forward]
Investment in equity method investees, September 30, 2018	660,254	$ 660,254		$ 660,254
September cash distributions	2,912
Impairment loss	1,837
Basis difference	(120,170)
Investment in equity method investees, net of basis difference, August 31, 2018	$ 544,833

EQUITY METHOD INVESTMENTS - Sta

EQUITY METHOD INVESTMENTS - Statements of Operations Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2018	Aug. 31, 2017
OGC
Schedule Of Equity Method Investments [Line Items]
Total revenues	$ 37,180	$ 35,144	$ 106,263	$ 103,302
Total operating expenses	31,751	25,720	94,044	86,046
Net income (loss)	5,429	9,424	12,213	17,258
OCC
Schedule Of Equity Method Investments [Line Items]
Total revenues	2,465	1,814	7,024	5,871
Total operating expenses	2,323	1,877	6,422	6,186
Net income (loss)	$ (5)	$ (204)	$ 116	$ (1,396)

DEFERRED REVENUE - Rollforward

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 4,000
Current deferred revenue, Additions	19,526
Current deferred revenue, Less revenue recognized	18,462
Current deferred revenue, ending balance	11,152
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	13,188
Noncurrent deferred revenue, Less reclassification to current deferred revenue	9,092
Noncurrent deferred revenue, ending balance	39,624
Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	10,088
Noncurrent deferred revenue, beginning balance	35,528
Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	6,088
Noncurrent deferred revenue, beginning balance	22,821
Utica Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	14
Current deferred revenue, Less revenue recognized	14
Current deferred revenue, ending balance	18
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	14
Noncurrent deferred revenue, ending balance	25
Utica Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Noncurrent deferred revenue, beginning balance	39
Utica Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Noncurrent deferred revenue, beginning balance	39
Williston Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	1,367
Current deferred revenue, Less revenue recognized	985
Current deferred revenue, ending balance	1,399
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	1,851
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,296
Noncurrent deferred revenue, ending balance	4,770
Williston Basin | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,017
Noncurrent deferred revenue, beginning balance	4,215
Williston Basin | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,017
Noncurrent deferred revenue, beginning balance	4,215
Piceance/DJ Basins
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	4,000
Current deferred revenue, Additions	16,846
Current deferred revenue, Less revenue recognized	16,186
Current deferred revenue, ending balance	8,056
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	9,014
Noncurrent deferred revenue, Less reclassification to current deferred revenue	6,483
Noncurrent deferred revenue, ending balance	25,255
Piceance/DJ Basins | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	7,396
Noncurrent deferred revenue, beginning balance	22,724
Piceance/DJ Basins | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	3,396
Noncurrent deferred revenue, beginning balance	10,017
Barnett Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	1,236
Current deferred revenue, Less revenue recognized	1,214
Current deferred revenue, ending balance	1,641
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	2,323
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,236
Noncurrent deferred revenue, ending balance	9,304
Barnett Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,619
Noncurrent deferred revenue, beginning balance	8,217
Barnett Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,619
Noncurrent deferred revenue, beginning balance	8,217
Marcellus Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	63
Current deferred revenue, Less revenue recognized	63
Current deferred revenue, ending balance	38
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	63
Noncurrent deferred revenue, ending balance	270
Marcellus Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	333
Marcellus Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	$ 333

DEBT - Components of Long-Term

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Total long-term debt	$ 1,175,313	$ 1,051,192
SMP Holdings
Line of Credit Facility [Line Items]
Total long-term debt	1,175,313	1,051,192
SMP Holdings | Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility	384,000	261,000
SMP Holdings | Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Unsecured notes	300,000	300,000
Less unamortized debt issuance costs	(2,530)	(2,910)
SMP Holdings | Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Unsecured notes	500,000	500,000
Less unamortized debt issuance costs	$ (6,157)	$ (6,898)

DEBT - Components of Long-Ter_2

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - SMP Holdings	Sep. 30, 2018	Dec. 31, 2017
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	4.50%	4.07%
Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Stated interest rate	5.75%	5.75%

DEBT - Revolving Credit Facilit

DEBT - Revolving Credit Facility (Narrative) (Details) - Revolving credit facility	9 Months Ended
	Sep. 30, 2018USD ($)
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	0.375%
Interest rate at period end	4.50%
Unused portion under the facility	$ 866,000,000
Debt issuance costs	9,200,000
Debt defaults	$ 0
LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.25%
Minimum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility	0.30%
Minimum | ABR
Line of Credit Facility [Line Items]
Applicable margin	0.75%
Minimum | LIBOR
Line of Credit Facility [Line Items]
Applicable margin	1.75%
Maximum
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the facility	0.50%
Maximum | ABR
Line of Credit Facility [Line Items]
Applicable margin	1.75%
Maximum | LIBOR
Line of Credit Facility [Line Items]
Applicable margin	2.75%

DEBT - Senior Notes (Narrative)

DEBT - Senior Notes (Narrative) (Details) - USD ($)	Jul. 31, 2014	Jul. 31, 2014	Feb. 08, 2017
5.75% Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%	5.75%	5.75%
Debt face amount			$ 500,000,000
Summit Holdings and Finance Corporation | Senior Notes Due August 2022
Debt Instrument [Line Items]
Senior unsecured notes	$ 300,000,000	$ 300,000,000
Stated interest rate	5.50%	5.50%
Maturity date	Aug. 15, 2022
Finance Corp | Summit Holdings
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary		100.00%

FINANCIAL INSTRUMENTS - Concent

FINANCIAL INSTRUMENTS - Concentration Risk - Narrative (Details) - Customer	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
CONCENTRATIONS OF RISK
Number of top customers	5
Five Largest Customers | Accounts receivable | Customer concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage	46.00%	44.00%

FINANCIAL INSTRUMENTS - Fair Va

FINANCIAL INSTRUMENTS - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 liability, beginning of period	$ 362,959
Change in fair value	53,759
Level 3 liability, end of period	$ 416,718

FINANCIAL INSTRUMENTS - Fair _2

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying value | 5.5% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 297,470	$ 297,090
Carrying value | Senior Notes 5.75%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	493,843	493,102
Fair Value | 5.5% Senior Notes | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	300,000	301,750
Fair Value | Senior Notes 5.75% | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 481,250	$ 501,667

FINANCIAL INSTRUMENTS - Fair _3

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Parenthetical) (Details) - Summit Holdings - USD ($)	Sep. 30, 2018	Dec. 31, 2017
5.5% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	5.50%	5.50%
Debt face amount	$ 300,000,000	$ 300,000,000
Senior Notes 5.75%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	5.75%
Debt face amount	$ 500,000,000

PARTNERS' CAPITAL - Partners' C

PARTNERS' CAPITAL - Partners' Capital and Schedule of Units (Details)	9 Months Ended
	Sep. 30, 2018shares
Series A Preferred Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	300,000
Units, ending balance (in shares)	300,000
Net units issued under the SMLP LTIP (in shares)	0
Common
Rollforwards of the number of partner units
Units, beginning balance (in shares)	73,085,996
Units, ending balance (in shares)	73,355,775
Net units issued under the SMLP LTIP (in shares)	269,779
General Partner Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	1,490,999
Units, ending balance (in shares)	1,490,999
Net units issued under the SMLP LTIP (in shares)	0

PARTNERS' CAPITAL - Narrative (

PARTNERS' CAPITAL - Narrative (Details) $ / shares in Units, $ in Millions	Oct. 25, 2018USD ($)$ / shares	Sep. 30, 2018USD ($)Transaction$ / sharesshares	Sep. 30, 2017$ / shares	Sep. 30, 2018USD ($)Transaction$ / sharesshares	Sep. 30, 2017$ / shares	Dec. 31, 2017USD ($)$ / sharesshares
Partners Capital [Line Items]
Preferred units issued | shares		300,000		300,000		300,000
Per-unit annual distributions to unitholders (in dollars per unit)		$ 0.575	$ 0.575	$ 1.725	$ 1.725
Surplus in excess (in dollars per share)				$ 0.46
Subsequent Event
Partners Capital [Line Items]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.575
Cash paid to unit holders | $	$ 45.2
Cash distribution date	Nov. 14, 2018
Cash distribution date of record	Nov. 7, 2018
Series A Preferred Units
Partners Capital [Line Items]
Preferred units issued | shares						300,000
Interest in partnership per unit						$ 1,000
Common | Public Offering
Partners Capital [Line Items]
Aggregate offering price | $						$ 150
Transactions under ATM Program | Transaction		0		0
Aggregate offering price | $		$ 132.3		$ 132.3
General Partner
Partners Capital [Line Items]
Percentage interest in distributions (maximum)				50.00%

PARTNERS' CAPITAL - Cash Distri

PARTNERS' CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.575	$ 0.575	$ 1.725	$ 1.725

PARTNERS' CAPITAL - Incentive D

PARTNERS' CAPITAL - Incentive Distribution Rights (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
IDR payments	$ 2,136	$ 2,127	$ 6,400	$ 6,333

EARNINGS PER UNIT (Details)

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ 54,151	$ 89,547	$ (2,948)	$ 95,576
Phantom Units
Earnings (loss) per limited partner unit:
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU (in shares)	1	0	2	55
Series A Preferred Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ 7,125	$ 0	$ 21,375	$ 0
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ 47,026	$ 89,547	$ (24,323)	$ 95,576
Weighted-average units outstanding (in shares)	73,356	73,059	73,283	72,583
Effect of nonvested phantom units (in shares)	400	374	0	318
Weighted-average units outstanding – diluted (shares)	73,756	73,433	73,283	72,901
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.64	$ 1.23	$ (0.33)	$ 1.32
Diluted (in dollars per share)	$ 0.64	$ 1.22	$ (0.33)	$ 1.31

UNIT-BASED AND NONCASH COMPEN_2

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) - SMLP LTIP - $ / shares	1 Months Ended
	Mar. 31, 2018	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units remaining available (in shares)		3,200,000
Phantom Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted units (in shares)	515,358
Grant date fair value (in dollars per share)	$ 15.25
Vesting period (years)	3 years
Units vested (in shares)	328,388

RELATED-PARTY TRANSACTIONS - Ex

RELATED-PARTY TRANSACTIONS - Expenses Incurred by the General Partner and Reimbursed (Details) - General Partner - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operation and maintenance expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 7,161	$ 6,792	$ 21,898	$ 20,404
General and administrative expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 7,220	$ 6,840	$ 22,818	$ 23,030

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Rent expense	$ 957	$ 1,009	$ 2,935	$ 2,811

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($)	1 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2017	Sep. 30, 2018	Dec. 31, 2015
Maximum | Meadowlark Midstream Gathering System | Principal Owner
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy		$ 25,000,000	$ 25,000,000
Coverage from property and business interruption insurance policy		$ 200,000,000
Business Interruption
Loss Contingencies [Line Items]
Recoveries recognized	$ 2,600,000
Property Recoveries
Loss Contingencies [Line Items]
Recoveries recognized	$ 400,000

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 5,344
Payments made	(3,060)
Additional accruals	1,600
Accrued environmental remediation, ending balance	$ 3,884

ACQUISITIONS AND DROP DOWN TR_2

ACQUISITIONS AND DROP DOWN TRANSACTIONS - 2016 Drop Down (Details) - USD ($) $ in Thousands	Mar. 03, 2016	Jun. 30, 2016	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Deferred purchase price obligation			$ 416,718	$ 362,959
Drop Down Assets 2016 Acquisition
Business Acquisition [Line Items]
Initial payment	$ 360,000
Working capital adjustment		$ 600
Estimated future payment obligation			470,900
Deferred purchase price obligation			$ 416,700
Discount rate			8.50%

CONDENSED CONSOLIDATING FINAN_3

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 370		$ 1,430	$ 2,911	$ 7,428
Accounts receivable	85,458		72,301
Other current assets	4,360		4,327
Due from affiliate			0
Total current assets	90,188		78,058
Property, plant and equipment, net	1,911,630	$ 1,828,252	1,795,129
Intangible assets, net	281,207		301,345
Goodwill	16,211		16,211
Investment in equity method investees	660,254		690,485
Other noncurrent assets	18,566		13,565
Investment in subsidiaries			0
Total assets	2,978,056		2,894,793
Liabilities and Partners' Capital
Trade accounts payable	22,569		16,375
Accrued expenses	18,347		12,499
Due to affiliate	13		1,088
Deferred revenue	11,152	10,088	4,000
Ad valorem taxes payable	8,223		8,329
Accrued interest	15,285		12,310
Accrued environmental remediation	2,702		3,130
Other current liabilities	10,388		11,258
Total current liabilities	88,679		68,989
Long-term debt	1,175,313		1,051,192
Deferred Purchase Price Obligation	416,718		362,959
Noncurrent deferred revenue	39,624	$ 35,528	12,707
Noncurrent accrued environmental remediation	1,182		2,214
Other noncurrent liabilities	5,525		7,063
Total liabilities	1,727,041		1,505,124
Total partners' capital	1,251,015		1,389,669	1,161,308	1,169,673
Total liabilities and partners' capital	2,978,056		2,894,793
Consolidating adjustments
Assets
Cash and cash equivalents	0		0	0	0
Accounts receivable			0
Other current assets			0
Due from affiliate	(581,988)		(515,097)
Total current assets	(581,988)		(515,097)
Property, plant and equipment, net			0
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets			0
Investment in subsidiaries	(5,514,884)		(5,344,164)
Total assets	(6,096,872)		(5,859,261)
Liabilities and Partners' Capital
Trade accounts payable			0
Accrued expenses			0
Due to affiliate	(581,988)		(515,097)
Deferred revenue			0
Ad valorem taxes payable			0
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities			0
Total current liabilities	(581,988)		(515,097)
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities			0
Total liabilities	(581,988)		(515,097)
Total partners' capital	(5,514,884)		(5,344,164)
Total liabilities and partners' capital	(6,096,872)		(5,859,261)
Summit Midstream Partners, LP | Reportable Legal Entities
Assets
Cash and cash equivalents	29		126	492	698
Accounts receivable	22		22
Other current assets	843		1,188
Due from affiliate			0
Total current assets	894		1,336
Property, plant and equipment, net	5,134		4,206
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets	3,320		2,547
Investment in subsidiaries	2,082,686		2,019,700
Total assets	2,092,034		2,027,789
Liabilities and Partners' Capital
Trade accounts payable	219		209
Accrued expenses	725		928
Due to affiliate	413,900		263,935
Deferred revenue			0
Ad valorem taxes payable	14		0
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities	5,386		6,395
Total current liabilities	420,244		271,467
Long-term debt			0
Deferred Purchase Price Obligation	416,718		362,959
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities	4,057		3,694
Total liabilities	841,019		638,120
Total partners' capital	1,251,015		1,389,669
Total liabilities and partners' capital	2,092,034		2,027,789
Co-Issuers | Reportable Legal Entities
Assets
Cash and cash equivalents	3		75	51	51
Accounts receivable			0
Other current assets			0
Due from affiliate			0
Total current assets	3		75
Property, plant and equipment, net			0
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets	9,184		10,913
Investment in subsidiaries	3,432,198		3,324,464
Total assets	3,441,385		3,335,452
Liabilities and Partners' Capital
Trade accounts payable			0
Accrued expenses			0
Due to affiliate	168,101		252,250
Deferred revenue			0
Ad valorem taxes payable			0
Accrued interest	15,285		12,310
Accrued environmental remediation			0
Other current liabilities			0
Total current liabilities	183,386		264,560
Long-term debt	1,175,313		1,051,192
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities			0
Total liabilities	1,358,699		1,315,752
Total partners' capital	2,082,686		2,019,700
Total liabilities and partners' capital	3,441,385		3,335,452
Guarantor Subsidiaries | Reportable Legal Entities
Assets
Cash and cash equivalents	330		1,138	1,543	5,768
Accounts receivable	74,766		65,842
Other current assets	2,922		2,697
Due from affiliate	513,867		493,067
Total current assets	591,885		562,744
Property, plant and equipment, net	1,563,950		1,442,333
Intangible assets, net	255,317		278,958
Goodwill	16,211		16,211
Investment in equity method investees			0
Other noncurrent assets	6,062		105
Investment in subsidiaries			0
Total assets	2,433,425		2,300,351
Liabilities and Partners' Capital
Trade accounts payable	18,523		11,283
Accrued expenses	16,051		10,592
Due to affiliate			0
Deferred revenue	10,716		4,000
Ad valorem taxes payable	7,802		7,809
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities	4,488		4,385
Total current liabilities	57,580		38,069
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue	37,802		12,707
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities	1,437		3,293
Total liabilities	96,819		54,069
Total partners' capital	2,336,606		2,246,282
Total liabilities and partners' capital	2,433,425		2,300,351
Non-Guarantor Subsidiaries | Reportable Legal Entities
Assets
Cash and cash equivalents	8		91	$ 825	$ 911
Accounts receivable	10,670		6,437
Other current assets	595		442
Due from affiliate	68,121		22,030
Total current assets	79,394		29,000
Property, plant and equipment, net	342,546		348,590
Intangible assets, net	25,890		22,387
Goodwill			0
Investment in equity method investees	660,254		690,485
Other noncurrent assets			0
Investment in subsidiaries			0
Total assets	1,108,084		1,090,462
Liabilities and Partners' Capital
Trade accounts payable	3,827		4,883
Accrued expenses	1,571		979
Due to affiliate			0
Deferred revenue	436		0
Ad valorem taxes payable	407		520
Accrued interest			0
Accrued environmental remediation	2,702		3,130
Other current liabilities	514		478
Total current liabilities	9,457		9,990
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue	1,822		0
Noncurrent accrued environmental remediation	1,182		2,214
Other noncurrent liabilities	31		76
Total liabilities	12,492		12,280
Total partners' capital	1,095,592		1,078,182
Total liabilities and partners' capital	$ 1,108,084		$ 1,090,462

CONDENSED CONSOLIDATING FINAN_4

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 127,479	$ 124,945	$ 372,982	$ 362,542
Costs and expenses:
Cost of natural gas and NGLs	$ 26,879	$ 18,177	$ 71,549	$ 36,328
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 24,382	$ 22,303	$ 73,452	$ 70,011
General and administrative	11,740	13,289	39,666	40,370
Depreciation and amortization	26,743	28,927	80,204	86,184
Transaction costs	0	0	0	119
Loss (gain) on asset sales, net	6	460	(6)	530
Long-lived asset impairment	1,540	1,290	2,127	1,577
Total costs and expenses	91,290	84,446	266,992	235,119
Other income	58	79	78	214
Interest expense	(14,862)	(17,614)	(44,821)	(51,883)
Early extinguishment of debt	0	0	0	(22,020)
Deferred Purchase Price Obligation	37,204	70,499	(53,759)	54,674
Income before income taxes and (loss) income from equity method investees	58,589	93,463	7,488	108,408
Income tax benefit (expense)	35	(176)	(88)	(417)
(Loss) income from equity method investees	(1,169)	350	(3,703)	(3,691)
Equity in earnings of consolidated subsidiaries	0	0
Net income	57,455	93,637	$ 3,697	$ 104,300
Consolidating adjustments
Revenues:
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	$ 0	$ 0
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 0	$ 0
General and administrative	0	0
Depreciation and amortization	0	0
Loss (gain) on asset sales, net	0	0
Long-lived asset impairment	0	0
Total costs and expenses	0	0
Other income	0	0
Interest expense	0	0
Deferred Purchase Price Obligation	0	0
Income before income taxes and (loss) income from equity method investees	0	0
Income tax benefit (expense)	0	0
(Loss) income from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	(56,036)	(64,788)	$ (162,363)	$ (175,119)
Net income	(56,036)	(64,788)	(162,363)	(175,119)
Gathering Services and Related Fees
Revenues:
Total revenues	86,427	96,070	260,373	298,884
Gathering Services and Related Fees | Consolidating adjustments
Revenues:
Total revenues	0	0
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	34,017	22,940	92,025	44,655
Natural Gas, NGLs and Condensate Sales | Consolidating adjustments
Revenues:
Total revenues	0	0
Other Revenues
Revenues:
Total revenues	7,035	5,935	$ 20,584	$ 19,003
Other Revenues | Consolidating adjustments
Revenues:
Total revenues	0	0
Summit Midstream Partners, LP | Reportable Legal Entities
Revenues:
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	$ 0	$ 0
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 0	$ 0
General and administrative	0	0
Depreciation and amortization	429	352	$ 1,305	$ 660
Transaction costs				119
Loss (gain) on asset sales, net	0	0
Long-lived asset impairment	0	0
Total costs and expenses	429	352	1,305	779
Other income	58	79	78	214
Interest expense	0	0
Deferred Purchase Price Obligation	37,204	70,499	(53,759)	54,674
Income before income taxes and (loss) income from equity method investees	36,833	70,226	(54,986)	54,109
Income tax benefit (expense)	35	(176)	(88)	(417)
(Loss) income from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	20,587	23,587	58,771	50,608
Net income	57,455	93,637	$ 3,697	$ 104,300
Summit Midstream Partners, LP | Gathering Services and Related Fees | Reportable Legal Entities
Revenues:
Total revenues	0	0
Summit Midstream Partners, LP | Natural Gas, NGLs and Condensate Sales | Reportable Legal Entities
Revenues:
Total revenues	0	0
Summit Midstream Partners, LP | Other Revenues | Reportable Legal Entities
Revenues:
Total revenues	0	0
Co-Issuers | Reportable Legal Entities
Revenues:
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	$ 0	$ 0
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 0	$ 0
General and administrative	0	0
Depreciation and amortization	0	0
Loss (gain) on asset sales, net	0	0
Long-lived asset impairment	0	0
Total costs and expenses	0	0
Other income	0	0
Interest expense	(14,862)	(17,614)	$ (44,821)	$ (51,883)
Early extinguishment of debt				(22,020)
Deferred Purchase Price Obligation	0	0
Income before income taxes and (loss) income from equity method investees	(14,862)	(17,614)	(44,821)	(73,903)
Income tax benefit (expense)	0	0
(Loss) income from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	35,449	41,201	103,592	124,511
Net income	20,587	23,587	58,771	50,608
Co-Issuers | Gathering Services and Related Fees | Reportable Legal Entities
Revenues:
Total revenues	0	0
Co-Issuers | Natural Gas, NGLs and Condensate Sales | Reportable Legal Entities
Revenues:
Total revenues	0	0
Co-Issuers | Other Revenues | Reportable Legal Entities
Revenues:
Total revenues	0	0
Guarantor Subsidiaries | Reportable Legal Entities
Revenues:
Total revenues	113,837	110,969	328,438	315,808
Costs and expenses:
Cost of natural gas and NGLs	$ 26,879	$ 18,177	$ 71,549	$ 36,328
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 21,721	$ 20,217	$ 66,095	$ 64,405
General and administrative	10,535	11,919	34,786	35,283
Depreciation and amortization	22,863	25,247	68,500	75,772
Loss (gain) on asset sales, net	1	(82)	(74)	(11)
Long-lived asset impairment	275	696	862	698
Total costs and expenses	82,274	76,174	241,718	212,475
Other income	0	0
Interest expense	0	0
Deferred Purchase Price Obligation	0	0
Income before income taxes and (loss) income from equity method investees	31,563	34,795	86,720	103,333
Income tax benefit (expense)	0	0
(Loss) income from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	0	0
Net income	31,563	34,795	86,720	103,333
Guarantor Subsidiaries | Gathering Services and Related Fees | Reportable Legal Entities
Revenues:
Total revenues	73,014	82,152	216,371	252,344
Guarantor Subsidiaries | Natural Gas, NGLs and Condensate Sales | Reportable Legal Entities
Revenues:
Total revenues	34,017	22,940	92,025	44,655
Guarantor Subsidiaries | Other Revenues | Reportable Legal Entities
Revenues:
Total revenues	6,806	5,877	20,042	18,809
Non-Guarantor Subsidiaries | Reportable Legal Entities
Revenues:
Total revenues	13,642	13,976	$ 44,544	$ 46,734
Costs and expenses:
Cost of natural gas and NGLs	$ 0	$ 0
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 2,661	$ 2,086	$ 7,357	$ 5,606
General and administrative	1,205	1,370	4,880	5,087
Depreciation and amortization	3,451	3,328	10,399	9,752
Loss (gain) on asset sales, net	5	542	68	541
Long-lived asset impairment	1,265	594	1,265	879
Total costs and expenses	8,587	7,920	23,969	21,865
Other income	0	0
Interest expense	0	0
Deferred Purchase Price Obligation	0	0
Income before income taxes and (loss) income from equity method investees	5,055	6,056	20,575	24,869
Income tax benefit (expense)	0	0
(Loss) income from equity method investees	(1,169)	350	(3,703)	(3,691)
Equity in earnings of consolidated subsidiaries	0	0
Net income	3,886	6,406	16,872	21,178
Non-Guarantor Subsidiaries | Gathering Services and Related Fees | Reportable Legal Entities
Revenues:
Total revenues	13,413	13,918	44,002	46,540
Non-Guarantor Subsidiaries | Natural Gas, NGLs and Condensate Sales | Reportable Legal Entities
Revenues:
Total revenues	0	0
Non-Guarantor Subsidiaries | Other Revenues | Reportable Legal Entities
Revenues:
Total revenues	$ 229	$ 58	$ 542	$ 194

CONDENSED CONSOLIDATING FINAN_5

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Cash Flow Statement (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$ 166,492	$ 196,497
Cash flows from investing activities:
Capital expenditures	(137,033)	(86,206)
Proceeds from asset sale	496	2,300
Contributions to equity method investees	0	(21,581)
Other, net	(209)	(579)
Advances to affiliates	0	0
Net cash provided by (used in) investing activities	(136,746)	(106,066)
Cash flows from financing activities:
Distributions to unitholders		(134,066)
Borrowings under Revolving Credit Facility	202,000	177,500
Repayments under Revolving Credit Facility	(79,000)	(319,500)
Debt issuance costs	(334)	(15,891)
Payment of redemption and call premiums on senior notes	0	(17,913)
Proceeds from ATM Program common unit issuances, net of costs	0	17,251
Contribution from General Partner	0	465
Issuance of senior notes	0	500,000
Tender and redemption of senior notes	0	(300,000)
Other, net	(3,738)	(2,794)
Advances from affiliates	0	0
Net cash provided by (used in) financing activities	(30,806)	(94,948)
Net change in cash and cash equivalents	(1,060)	(4,517)
Cash and cash equivalents, beginning of period	1,430	7,428
Cash and cash equivalents, end of period	370	2,911
Consolidating adjustments
Cash flows from operating activities:
Net cash provided by (used in) operating activities	0	0
Cash flows from investing activities:
Capital expenditures	0	0
Proceeds from asset sale	0	0
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	151,040	91,269
Net cash provided by (used in) investing activities	151,040	91,269
Cash flows from financing activities:
Distributions to unitholders		0
Borrowings under Revolving Credit Facility	0	0
Repayments under Revolving Credit Facility	0	0
Debt issuance costs	0	0
Payment of redemption and call premiums on senior notes		0
Proceeds from ATM Program common unit issuances, net of costs		0
Contribution from General Partner		0
Issuance of senior notes		0
Tender and redemption of senior notes		0
Other, net	0	0
Advances from affiliates	(151,040)	(91,269)
Net cash provided by (used in) financing activities	(151,040)	(91,269)
Net change in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Summit Midstream Partners, LP | Reportable Legal Entities
Cash flows from operating activities:
Net cash provided by (used in) operating activities	3,687	5,707
Cash flows from investing activities:
Capital expenditures	(2,101)	(995)
Proceeds from asset sale	0	0
Contributions to equity method investees		0
Other, net	(209)	(579)
Advances to affiliates	0	11,768
Net cash provided by (used in) investing activities	(2,310)	10,194
Cash flows from financing activities:
Distributions to unitholders		(134,066)
Borrowings under Revolving Credit Facility	0	0
Repayments under Revolving Credit Facility	0	0
Debt issuance costs	0	0
Payment of redemption and call premiums on senior notes		0
Proceeds from ATM Program common unit issuances, net of costs		17,251
Contribution from General Partner		465
Issuance of senior notes		0
Tender and redemption of senior notes		0
Other, net	(2,780)	(2,794)
Advances from affiliates	151,040	103,037
Net cash provided by (used in) financing activities	(1,474)	(16,107)
Net change in cash and cash equivalents	(97)	(206)
Cash and cash equivalents, beginning of period	126	698
Cash and cash equivalents, end of period	29	492
Co-Issuers | Reportable Legal Entities
Cash flows from operating activities:
Net cash provided by (used in) operating activities	(38,590)	(45,854)
Cash flows from investing activities:
Capital expenditures	0	0
Proceeds from asset sale	0	0
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	(84,148)	21,658
Net cash provided by (used in) investing activities	(84,148)	21,658
Cash flows from financing activities:
Distributions to unitholders		0
Borrowings under Revolving Credit Facility	202,000	177,500
Repayments under Revolving Credit Facility	(79,000)	(319,500)
Debt issuance costs	(334)	(15,891)
Payment of redemption and call premiums on senior notes		(17,913)
Proceeds from ATM Program common unit issuances, net of costs		0
Contribution from General Partner		0
Issuance of senior notes		500,000
Tender and redemption of senior notes		(300,000)
Other, net	0	0
Advances from affiliates	0	0
Net cash provided by (used in) financing activities	122,666	24,196
Net change in cash and cash equivalents	(72)	0
Cash and cash equivalents, beginning of period	75	51
Cash and cash equivalents, end of period	3	51
Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from operating activities:
Net cash provided by (used in) operating activities	148,237	176,442
Cash flows from investing activities:
Capital expenditures	(127,362)	(64,413)
Proceeds from asset sale	0	0
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	(20,802)	(116,254)
Net cash provided by (used in) investing activities	(148,164)	(180,667)
Cash flows from financing activities:
Distributions to unitholders		0
Borrowings under Revolving Credit Facility	0	0
Repayments under Revolving Credit Facility	0	0
Debt issuance costs	0	0
Payment of redemption and call premiums on senior notes		0
Proceeds from ATM Program common unit issuances, net of costs		0
Contribution from General Partner		0
Issuance of senior notes		0
Tender and redemption of senior notes		0
Other, net	(881)	0
Advances from affiliates	0	0
Net cash provided by (used in) financing activities	(881)	0
Net change in cash and cash equivalents	(808)	(4,225)
Cash and cash equivalents, beginning of period	1,138	5,768
Cash and cash equivalents, end of period	330	1,543
Non-Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from operating activities:
Net cash provided by (used in) operating activities	53,158	60,202
Cash flows from investing activities:
Capital expenditures	(7,570)	(20,798)
Proceeds from asset sale	496	2,300
Contributions to equity method investees		(21,581)
Other, net	0	0
Advances to affiliates	(46,090)	(8,441)
Net cash provided by (used in) investing activities	(53,164)	(48,520)
Cash flows from financing activities:
Distributions to unitholders		0
Borrowings under Revolving Credit Facility	0	0
Repayments under Revolving Credit Facility	0	0
Debt issuance costs	0	0
Payment of redemption and call premiums on senior notes		0
Proceeds from ATM Program common unit issuances, net of costs		0
Contribution from General Partner		0
Issuance of senior notes		0
Tender and redemption of senior notes		0
Other, net	(77)	0
Advances from affiliates	0	(11,768)
Net cash provided by (used in) financing activities	(77)	(11,768)
Net change in cash and cash equivalents	(83)	(86)
Cash and cash equivalents, beginning of period	91	911
Cash and cash equivalents, end of period	8	825
Common units
Cash flows from financing activities:
Distributions to unitholders	(135,484)	(134,066)
Common units | Consolidating adjustments
Cash flows from financing activities:
Distributions to unitholders	0
Common units | Summit Midstream Partners, LP | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	(135,484)
Common units | Co-Issuers | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	0
Common units | Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	0
Common units | Non-Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	0
Series A Preferred Units
Cash flows from financing activities:
Distributions to unitholders	(14,250)	$ 0
Series A Preferred Units | Consolidating adjustments
Cash flows from financing activities:
Distributions to unitholders	0
Series A Preferred Units | Summit Midstream Partners, LP | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	(14,250)
Series A Preferred Units | Co-Issuers | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	0
Series A Preferred Units | Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	0
Series A Preferred Units | Non-Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from financing activities:
Distributions to unitholders	$ 0

SUBSEQUENT EVENTS - Narrative (

SUBSEQUENT EVENTS - Narrative (Details) - Utica Shale, Ohio Gathering and Williston Basin Segments - USD ($) $ in Millions	1 Months Ended
	Oct. 31, 2018	Sep. 30, 2018
Subsequent Event [Line Items]
Estimated future payment obligation		$ 470.9
Subsequent Event
Subsequent Event [Line Items]
Deferred purchase price obligation, change in amount	$ 16.9
Deferred purchase price obligation	$ 454