0001564590-18-010998 | 10-Q | XBRL Viewer | Summit Midstream Partners LP

FINANCIAL INSTRUMENTS (Tables)

3 Months Ended

Mar. 31, 2018

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		21,658
Level 3 liability, March 31, 2018	$	384,617

Summary of the estimated fair value of debt instruments

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

	March 31, 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)	$	297,253	$	292,250	$	297,090	$	301,750
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		493,349		475,000		493,102		501,667

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 3,366	$ 1,430
Accounts receivable	68,811	72,301
Other current assets	3,535	4,327
Total current assets	75,712	78,058
Property, plant and equipment, net	1,858,312	1,795,129
Intangible assets, net	293,771	301,345
Goodwill	16,211	16,211
Investment in equity method investees	682,227	690,485
Other noncurrent assets	13,153	13,565
Total assets	2,939,386	2,894,793
Current liabilities:
Trade accounts payable	21,232	16,375
Accrued expenses	13,971	12,499
Due to affiliate	443	1,088
Deferred revenue	10,159	4,000
Ad valorem taxes payable	3,834	8,329
Accrued interest	15,383	12,310
Accrued environmental remediation	3,068	3,130
Other current liabilities	5,984	11,258
Total current liabilities	74,074	68,989
Long-term debt	1,091,602	1,051,192
Deferred Purchase Price Obligation	384,617	362,959
Noncurrent deferred revenue	36,587	12,707
Noncurrent accrued environmental remediation	1,916	2,214
Other noncurrent liabilities	6,509	7,063
Total liabilities	1,595,305	1,505,124
Commitments and contingencies (Note 16)
Series A Preferred Units (300,000 units issued and outstanding at March 31, 2018 and December 31, 2017)	300,741	294,426
Common limited partner capital (73,355,775 units issued and outstanding at March 31, 2018 and 73,085,996 units issued and outstanding at December 31, 2017)	1,005,409	1,056,510
General Partner interests (1,490,999 units issued and outstanding at March 31, 2018 and December 31, 2017)	27,033	27,920
Noncontrolling interest	10,898	10,813
Total partners' capital	1,344,081	1,389,669
Total liabilities and partners' capital	$ 2,939,386	$ 2,894,793

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Noncontrolling interest	Common	General Partner	Limited partners, Series A Preferred Units
Beginning balance at Dec. 31, 2016	$ 1,169,673	$ 11,247	$ 1,129,132	$ 29,294
Net (loss) income	(583)	102	(2,777)	2,092
Distributions to unitholders	(44,452)	0	(41,464)	(2,988)
Unit-based compensation	2,048	0	2,048	0
Tax withholdings on vested SMLP LTIP awards	(2,051)	0	(2,051)	0
ATM Program issuances, net of costs	367	0	367	0
Contribution from General Partner	113	0	0	113
Ending balance at Mar. 31, 2017	1,125,115	11,349	1,085,255	28,511
January 1, 2018 impact of Topic 606day 1 adoption	4,214	0	4,130	84	$ 0
Beginning balance (Adjustment)	1,393,883	10,813	1,060,640	28,004	294,426
Beginning balance at Dec. 31, 2017	1,389,669	10,813	1,056,510	27,920	294,426
Net (loss) income	(3,845)	85	(13,113)	2,058	7,125
Distributions to unitholders	(45,053)	0	(42,024)	(3,029)	0
Unit-based compensation	1,979	0	1,979	0	0
Tax withholdings on vested SMLP LTIP awards	(1,943)	0	(1,943)	0	0
Other	(940)	0	(130)	0	(810)
Ending balance at Mar. 31, 2018	$ 1,344,081	$ 10,898	$ 1,005,409	$ 27,033	$ 300,741

SEGMENT INFORMATION - Concentration Risk (Details) - Revenue - Customer concentration	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Counterparty A - Piceance/DJ Basins
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	0.00%
Counterparty B - Williston Basin
Segment Reporting Information [Line Items]
Concentration risk, percentage	0.00%	32.00%

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying value \| 5.5% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 297,253	$ 297,090
Carrying value \| Senior Notes 5.75%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	493,349	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	292,250	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	$ 475,000	$ 501,667

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

3 Months Ended

Mar. 31, 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

	March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Assets
Accounts receivable	$	68,811	$	66,386	$	2,425
Property, plant and equipment, net		1,858,312		1,824,484		33,828

Liabilities
Deferred revenue, current		10,159		4,071		6,088
Deferred revenue, noncurrent		36,587		12,707		23,880

Partners' Capital (1)		1,032,442		1,026,157		6,285

________

(1) Includes common limited partner capital and general partner interests.

Unaudited condensed consolidated statement of operations

	Three months ended March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Revenues
Gathering services and related fees	$	84,361	$	85,303	$	(942	)
Costs and expenses
Cost of natural gas and NGLs		20,286		23,602		(3,316	)
Depreciation and amortization		26,677		26,374		303

Unaudited condensed consolidated statement of cash flows

	Three months ended March 31, 2018
	As Reported			Balances Without Adoption of Topic 606			Effect of Change Increase / (Decrease)
	(In thousands)
Cash flows from operating activities:
Net loss	$	(3,845	)	$	(5,916	)	$	2,071
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization		26,526			26,223			303
Cash flows from operating activities:
Accounts receivable		3,490			5,915			(2,425	)
Deferred revenue, net		1,130			1,079			51

•

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. We have not yet adopted the following accounting pronouncements as of March 31, 2018:

•

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.

•

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.

DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Total long-term debt	$ 1,091,602	$ 1,051,192
SMP Holdings
Line of Credit Facility [Line Items]
Total long-term debt	1,091,602	1,051,192
SMP Holdings \| Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility	301,000	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	(2,747)	(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	$ (6,651)	$ (6,898)

PARTNERS' CAPITAL - Incentive Distribution Rights (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
IDR payments	$ 2,128	$ 2,100

REVENUE - Schedule of Estimated Revenue Expected to be Recognized and MVC Shortfall Payments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
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	9 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	$ 115,834
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	133,743
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	$ 174,227

DEFERRED REVENUE

3 Months Ended

Mar. 31, 2018

Deferred Revenue Disclosure [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		5		325		5,344		400		9		6,083
Less revenue recognized		5		254		5,344		400		9		6,012
Current deferred revenue, March 31, 2018	$	18	$	1,088	$	7,396	$	1,619	$	38	$	10,159

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		—		—		2,833		724		—		3,557
Less reclassification to current deferred revenue		5		254		1,830		400		9		2,498
Noncurrent deferred revenue, March 31, 2018	$	34	$	3,961	$	23,727	$	8,541	$	324	$	36,587

EQUITY METHOD INVESTMENTS - Statements of Operations Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2018	Feb. 28, 2017
OGC
Schedule Of Equity Method Investments [Line Items]
Total revenues	$ 34,960	$ 37,075
Total operating expenses	26,775	27,105
Net income (loss)	8,180	7,973
OCC
Schedule Of Equity Method Investments [Line Items]
Total revenues	2,489	2,053
Total operating expenses	2,141	2,473
Net income (loss)	$ 180	$ (1,215)

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - Meadowlark Midstream Gathering System $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrued environmental remediation, beginning balance	$ 5,344
Payments made	(360)
Accrued environmental remediation, ending balance	$ 4,984

SUBSEQUENT EVENTS - Narrative (Details) - Utica Shale - USD ($) $ in Millions	1 Months Ended
	Apr. 30, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Deferred purchase price obligation		$ 467.5
Subsequent Event
Subsequent Event [Line Items]
Deferred purchase price obligation, change in amount	$ 49.6
Deferred purchase price obligation	$ 517.1

RELATED-PARTY TRANSACTIONS - Expenses Incurred by the General Partner and Reimbursed (Details) - General Partner - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operation and maintenance expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 7,623	$ 6,881
General and administrative expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 8,117	$ 8,295

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 80,932	$ 81,503
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	8,715	7,912
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,477	9,073
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	15,970	17,809
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Adjusted EBITDA	29,235	28,974
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	9,859	12,088
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 6,676	$ 5,647

DEBT - Revolving Credit Facility (Narrative) (Details) - Revolving credit facility	3 Months Ended
	Mar. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,250,000,000
Revolving credit facility maturity date	2022-05
Accordion feature	$ 250,000,000.0
Commitment fee on unused portion of the facility	0.375%
Interest rate at period end	3.90%
Unused portion under the facility	$ 949,000,000.0
Debt issuance costs	10,300,000
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%

CONDENSED CONSOLIDATING FINANCIAL INFORMATION

3 Months Ended

Mar. 31, 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 March 31, 2018 and December 31, 2017 follow.

	March 31, 2018
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	213	$	368	$	2,331	$	454	$	—		$	3,366
Accounts receivable		22		—		60,378		8,411		—			68,811
Other current assets		1,194		—		1,955		386		—			3,535
Due from affiliate		—		—		500,061		37,581		(537,642	)		—
Total current assets		1,429		368		564,725		46,832		(537,642	)		75,712
Property, plant and equipment, net		4,063		—		1,504,830		349,419		—			1,858,312
Intangible assets, net		—		—		271,504		22,267		—			293,771
Goodwill		—		—		16,211		—		—			16,211
Investment in equity method investees		—		—		—		682,227		—			682,227
Other noncurrent assets		2,768		10,286		99		—		—			13,153
Investment in subsidiaries		2,041,996		3,361,858		—		—		(5,403,854	)		—
Total assets	$	2,050,256	$	3,372,512	$	2,357,369	$	1,100,745	$	(5,941,496	)	$	2,939,386

Liabilities and Partners' Capital
Trade accounts payable	$	56	$	—	$	16,822	$	4,354	$	—		$	21,232
Accrued expenses		940		—		11,607		1,424		—			13,971
Due to affiliate		314,554		223,531		—		—		(537,642	)		443
Deferred revenue		—		—		9,722		437		—			10,159
Ad valorem taxes payable		5		—		3,693		136		—			3,834
Accrued interest		—		15,383		—		—		—			15,383
Accrued environmental remediation		—		—		—		3,068		—			3,068
Other current liabilities		2,314		—		3,338		332		—			5,984
Total current liabilities		317,869		238,914		45,182		9,751		(537,642	)		74,074
Long-term debt		—		1,091,602		—		—		—			1,091,602
Deferred Purchase Price Obligation		384,617		—		—		—		—			384,617
Noncurrent deferred revenue		—		—		34,775		1,812		—			36,587
Noncurrent accrued environmental remediation		—		—		—		1,916		—			1,916
Other noncurrent liabilities		3,689		—		2,744		76		—			6,509
Total liabilities		706,175		1,330,516		82,701		13,555		(537,642	)		1,595,305

Total partners' capital		1,344,081		2,041,996		2,274,668		1,087,190		(5,403,854	)		1,344,081
Total liabilities and partners' capital	$	2,050,256	$	3,372,512	$	2,357,369	$	1,100,745	$	(5,941,496	)	$	2,939,386

	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
Noncurrent 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 months ended March 31, 2018 and 2017 follow.

	Three months ended March 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	69,466		$	14,895	$	—		$	84,361
Natural gas, NGLs and condensate sales		—			—			26,117			—		—			26,117
Other revenues		—			—			6,727			115		—			6,842
Total revenues		—			—			102,310			15,010		—			117,320
Costs and expenses:
Cost of natural gas and NGLs		—			—			20,286			—		—			20,286
Operation and maintenance		—			—			22,153			2,451		—			24,604
General and administrative		—			—			12,287			2,098		—			14,385
Depreciation and amortization		432			—			22,861			3,384		—			26,677
Transaction costs		57			—			—			—		—			57
Gain on asset sales, net		—			—			(74	)				—			(74	)
Total costs and expenses		489			—			77,513			7,933		—			85,935
Other expense		(7	)		—			—			—		—			(7	)
Interest expense		—			(15,122	)		—			—		—			(15,122	)
Deferred Purchase Price Obligation		(21,658	)		—			—			—		—			(21,658	)
(Loss) income before income taxes and income from equity method investees		(22,154	)		(15,122	)		24,797			7,077		—			(5,402	)
Income tax benefit		171			—			—			—		—			171
Income from equity method investees		—			—			—			1,386		—			1,386
Equity in earnings of consolidated subsidiaries		18,138			33,260			—			—		(51,398	)		—
Net (loss) income	$	(3,845	)	$	18,138		$	24,797		$	8,463	$	(51,398	)	$	(3,845	)

	Three months ended March 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	102,513	$	15,500		$	—		$	118,013
Natural gas, NGLs and condensate sales		—			—			11,120		—			—			11,120
Other revenues		—			—			6,600		72			—			6,672
Total revenues		—			—			120,233		15,572			—			135,805
Costs and expenses:
Cost of natural gas and NGLs		—			—			9,052		—			—			9,052
Operation and maintenance		—			—			22,020		1,672			—			23,692
General and administrative		—			—			12,485		1,647			—			14,132
Depreciation and amortization		154			—			25,242		3,173			—			28,569
Loss on asset sales, net		—			—			3		—			—			3
Long-lived asset impairment		—			—			—		284			—			284
Total costs and expenses		154			—			68,802		6,776			—			75,732
Other income		71			—			—		—			—			71
Interest expense		—			(16,716	)		—		—			—			(16,716	)
Early extinguishment of debt		—			(22,020	)		—		—			—			(22,020	)
Deferred Purchase Price Obligation		(20,883	)		—			—		—			—			(20,883	)
(Loss) income before income taxes and loss from equity method investees		(20,966	)		(38,736	)		51,431		8,796			—			525
Income tax expense		(452	)		—			—		—			—			(452	)
Loss from equity method investees		—			—			—		(656	)		—			(656	)
Equity in earnings of consolidated subsidiaries		20,835			59,571			—		—			(80,406	)		—
Net (loss) income	$	(583	)	$	20,835		$	51,431	$	8,140		$	(80,406	)	$	(583	)

Condensed Consolidating Statements of Cash Flows. Statements of cash flows for the three months ended March 31, 2018 and 2017 follow.

	March 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$	(2,721	)	$	(10,985	)	$	47,495		$	17,421		$	—		$	51,210

Cash flows from investing activities:
Capital expenditures		(297	)		—			(39,001	)		(1,480	)		—			(40,778	)
Other, net		(221	)		—			—			—			—			(221	)
Advances to affiliates		—			(28,718	)		(6,995	)		(15,549	)		51,262			—
Net cash used in investing activities		(518	)		(28,718	)		(45,996	)		(17,029	)		51,262			(40,999	)

Cash flows from financing activities:
Distributions to unitholders		(45,053	)		—			—			—			—			(45,053	)
Borrowings under Revolving Credit Facility		—			50,000			—			—			—			50,000
Repayments under Revolving Credit Facility		—			(10,000	)		—			—			—			(10,000	)
Debt issuance costs		—			(4	)		—			—			—			(4	)
Other, net		(2,883	)		—			(306	)		(29	)		—			(3,218	)
Advances from affiliates		51,262			—			—			—			(51,262	)		—
Net cash provided by (used in) financing activities		3,326			39,996			(306	)		(29	)		(51,262	)		(8,275	)
Net change in cash and cash equivalents		87			293			1,193			363			—			1,936
Cash and cash equivalents, beginning of period		126			75			1,138			91			—			1,430
Cash and cash equivalents, end of period	$	213		$	368		$	2,331		$	454		$	—		$	3,366

	March 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$	(2,021	)	$	(27,574	)	$	75,271		$	16,773		$	—		$	62,449

Cash flows from investing activities:
Capital expenditures		(1,003	)		—			(6,089	)		(7,336	)		—			(14,428	)
Contributions to equity method investees		—			—			—			(4,936	)		—			(4,936	)
Other, net		(361	)		—			—			—			—			(361	)
Advances to affiliates		(20,185	)		—			(72,075	)		—			92,260			—
Net cash used in investing activities		(21,549	)		—			(78,164	)		(12,272	)		92,260			(19,725	)

Cash flows from financing activities:
Distributions to unitholders		(44,452	)		—			—			—			—			(44,452	)
Borrowings under Revolving Credit Facility		—			72,000			—			—			—			72,000
Repayments under Revolving Credit Facility		—			(245,000	)		—			—			—			(245,000	)
Debt issuance costs		—			(6,825	)		—			—			—			(6,825	)
Payment of redemption and call premiums on senior notes		—			(17,913	)		—			—			—			(17,913	)
Proceeds from ATM Program issuances, net of costs		367			—			—			—			—			367
Contribution from General Partner		113			—			—			—			—			113
Issuance of senior notes		—			500,000			—			—			—			500,000
Tender and redemption of senior notes		—			(300,000	)		—			—			—			(300,000	)
Other, net		(2,051	)		—			(91	)		(15	)		—			(2,157	)
Advances from affiliates		72,075			25,266			—			(5,081	)		(92,260	)		—
Net cash provided by (used in) financing activities		26,052			27,528			(91	)		(5,096	)		(92,260	)		(43,867	)
Net change in cash and cash equivalents		2,482			(46	)		(2,984	)		(595	)		—			(1,143	)
Cash and cash equivalents, beginning of period		698			51			5,768			911			—			7,428
Cash and cash equivalents, end of period	$	3,180		$	5		$	2,784		$	316		$	—		$	6,285

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Impact of Topic 606 Adoption on Unaudited Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 68,811
Property, plant and equipment, net	1,858,312	$ 1,828,252	$ 1,795,129
Liabilities
Deferred revenue	10,159	10,088	4,000
Deferred revenue, noncurrent	36,587	35,528	12,707
Partners' Capital	1,032,442	1,088,644
Balances Without Adoption of Topic 606
Assets
Accounts receivable	66,386
Property, plant and equipment, net	1,824,484		1,795,129
Liabilities
Deferred revenue	4,071		4,000
Deferred revenue, noncurrent	12,707		12,707
Partners' Capital	1,026,157		1,084,430
Effect of Change Increase / (Decrease)
Liabilities
Deferred revenue			6,088
Deferred revenue, noncurrent			$ 22,821
Accounting Standard Update 2014-09 \| Effect of Change Increase / (Decrease)
Assets
Accounts receivable	2,425
Property, plant and equipment, net	33,828	33,123
Liabilities
Deferred revenue	6,088	6,088
Deferred revenue, noncurrent	23,880	22,821
Partners' Capital	$ 6,285	$ 4,214

DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 4,000
Current deferred revenue, Additions	6,083
Current deferred revenue, Less revenue recognized	6,012
Current deferred revenue, ending balance	10,159
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	3,557
Noncurrent deferred revenue, Less reclassification to current deferred revenue	2,498
Noncurrent deferred revenue, ending balance	36,587
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
Adjustment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	10,088
Noncurrent deferred revenue, beginning balance	35,528
Utica Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	5
Current deferred revenue, Less revenue recognized	5
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	5
Noncurrent deferred revenue, ending balance	34
Utica Shale \| Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Noncurrent deferred revenue, beginning balance	39
Utica Shale \| Adjustment
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	325
Current deferred revenue, Less revenue recognized	254
Current deferred revenue, ending balance	1,088
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	254
Noncurrent deferred revenue, ending balance	3,961
Williston Basin \| 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
Williston Basin \| Adjustment
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	5,344
Current deferred revenue, Less revenue recognized	5,344
Current deferred revenue, ending balance	7,396
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	2,833
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,830
Noncurrent deferred revenue, ending balance	23,727
Piceance/DJ Basins \| 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
Piceance/DJ Basins \| Adjustment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	7,396
Noncurrent deferred revenue, beginning balance	22,724
Barnett Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	400
Current deferred revenue, Less revenue recognized	400
Current deferred revenue, ending balance	1,619
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	724
Noncurrent deferred revenue, Less reclassification to current deferred revenue	400
Noncurrent deferred revenue, ending balance	8,541
Barnett Shale \| 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
Barnett Shale \| Adjustment
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	9
Current deferred revenue, Less revenue recognized	9
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	9
Noncurrent deferred revenue, ending balance	324
Marcellus Shale \| Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	333
Marcellus Shale \| Adjustment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	$ 333

ACQUISITIONS AND DROP DOWN TRANSACTIONS

3 Months Ended

Mar. 31, 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 $360.0 million funded with borrowings under our Revolving Credit Facility and a $0.6 million working

capital adjustment received in June 2016 (the “Initial Payment”) and (ii) includes the Deferred Purchase Price Obligation payment due in 2020.

The present value of the Deferred Purchase Price Obligation is reflected as a liability on our balance sheet until paid. As of March 31, 2018, Remaining Consideration was estimated to be $467.5 million and the net present value, as recognized on the consolidated balance sheet, was $384.6 million, using a discount rate of 10.25%. Any subsequent changes to the estimated future payment obligation will be calculated using a discounted cash flow model with a commensurate risk-adjusted discount rate. Such changes and the impact on the liability due to the passage of time will be recorded as a change in the Deferred Purchase Price Obligation fair value on the consolidated statements of operations in the period of the change.

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.

REVENUE - Schedule of Disaggregated Revenue by Geographic Area and Major Products and Services Reportable Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Disaggregation Of Revenue [Line Items]
Revenue	$ 117,320
Utica Shale
Disaggregation Of Revenue [Line Items]
Revenue	10,041
Williston Basin
Disaggregation Of Revenue [Line Items]
Revenue	28,424
Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Revenue	41,587
Barnett Shale
Disaggregation Of Revenue [Line Items]
Revenue	16,170
Marcellus Shale
Disaggregation Of Revenue [Line Items]
Revenue	7,825
Total Reportable Segments
Disaggregation Of Revenue [Line Items]
Revenue	104,047
All Other Segments
Disaggregation Of Revenue [Line Items]
Revenue	13,273
Gathering Services and Related Fees
Disaggregation Of Revenue [Line Items]
Revenue	84,361
Gathering Services and Related Fees \| Utica Shale
Disaggregation Of Revenue [Line Items]
Revenue	10,041
Gathering Services and Related Fees \| Williston Basin
Disaggregation Of Revenue [Line Items]
Revenue	17,666
Gathering Services and Related Fees \| Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Revenue	35,294
Gathering Services and Related Fees \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Revenue	13,637
Gathering Services and Related Fees \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Revenue	7,825
Gathering Services and Related Fees \| Total Reportable Segments
Disaggregation Of Revenue [Line Items]
Revenue	84,463
Gathering Services and Related Fees \| All Other Segments
Disaggregation Of Revenue [Line Items]
Revenue	(102)
Natural Gas, NGLs and Condensate Sales
Disaggregation Of Revenue [Line Items]
Revenue	26,117
Natural Gas, NGLs and Condensate Sales \| Utica Shale
Disaggregation Of Revenue [Line Items]
Revenue	0
Natural Gas, NGLs and Condensate Sales \| Williston Basin
Disaggregation Of Revenue [Line Items]
Revenue	7,846
Natural Gas, NGLs and Condensate Sales \| Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Revenue	4,325
Natural Gas, NGLs and Condensate Sales \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Revenue	545
Natural Gas, NGLs and Condensate Sales \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Revenue	0
Natural Gas, NGLs and Condensate Sales \| Total Reportable Segments
Disaggregation Of Revenue [Line Items]
Revenue	12,716
Natural Gas, NGLs and Condensate Sales \| All Other Segments
Disaggregation Of Revenue [Line Items]
Revenue	13,401
Other Revenues
Disaggregation Of Revenue [Line Items]
Revenue	6,842
Other Revenues \| Utica Shale
Disaggregation Of Revenue [Line Items]
Revenue	0
Other Revenues \| Williston Basin
Disaggregation Of Revenue [Line Items]
Revenue	2,912
Other Revenues \| Piceance/DJ Basins
Disaggregation Of Revenue [Line Items]
Revenue	1,968
Other Revenues \| Barnett Shale
Disaggregation Of Revenue [Line Items]
Revenue	1,988
Other Revenues \| Marcellus Shale
Disaggregation Of Revenue [Line Items]
Revenue	0
Other Revenues \| Total Reportable Segments
Disaggregation Of Revenue [Line Items]
Revenue	6,868
Other Revenues \| All Other Segments
Disaggregation Of Revenue [Line Items]
Revenue	$ (26)

SEGMENT INFORMATION - Narrative (Details) - USD ($)	3 Months Ended
SEGMENT INFORMATION - Narrative (Details) - USD ($)	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting [Abstract]
Adjustments related to MVC shortfall payments	$ 0	$ (28,640,000)

SEGMENT INFORMATION - Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments		$ (38,485,000)
Expected MVC shortfall adjustments		9,845,000
Total adjustments related to MVC shortfall payments	$ 0	(28,640,000)
Williston Basin
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments		(37,693,000)
Expected MVC shortfall adjustments		1,982,000
Total adjustments related to MVC shortfall payments		(35,711,000)
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments		(792,000)
Expected MVC shortfall adjustments		6,545,000
Total adjustments related to MVC shortfall payments		5,753,000
Barnett Shale
Segment Reporting Information [Line Items]
Net change in deferred revenue for MVC shortfall payments		0
Expected MVC shortfall adjustments		1,318,000
Total adjustments related to MVC shortfall payments		$ 1,318,000

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
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (3,845)	$ (583)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	26,526	28,418
Cash flows from operating activities:
Accounts receivable	3,490	43,695
Deferred revenue, net	1,130	$ (38,485)
Balances Without Adoption of Topic 606
Cash flows from operating activities:
Net loss	(5,916)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	26,223
Cash flows from operating activities:
Accounts receivable	5,915
Deferred revenue, net	1,079
Accounting Standard Update 2014-09 \| Effect of Change Increase / (Decrease)
Cash flows from operating activities:
Net loss	2,071
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	303
Cash flows from operating activities:
Accounts receivable	(2,425)
Deferred revenue, net	$ 51

GOODWILL - Narrative (Details)	3 Months Ended
GOODWILL - Narrative (Details)	Mar. 31, 2018 USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

FINANCIAL INSTRUMENTS - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
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	21,658
Level 3 liability, end of period	$ 384,617

PARTNERS' CAPITAL

3 Months Ended

Mar. 31, 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, March 31, 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 months ended March 31, 2018, there were no transactions under the ATM Program. Following the effectiveness of the new ATM registration statement and after taking into account the aggregate sales price of common units sold under the ATM Program through March 31, 2018, we have the capacity to issue additional common units under the ATM Program up to an aggregate $132.3 million.

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 months ended March 31:

	Three months ended March 31,
	2018		2017
Per-unit distributions to unitholders	$	0.575	$	0.575

On April 26, 2018, the Board of Directors of our General Partner declared a distribution of $0.575 per unit for the quarterly period ended March 31, 2018. This distribution, which totaled $45.2 million, will be paid on May 15, 2018 to unitholders of record at the close of business on May 8, 2018.

Incentive Distribution Rights. Our general partner also currently holds IDRs that entitle it to receive increasing percentage allocations, up to a maximum of 50%, of the cash we distribute from operating surplus in excess of $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 months ended March 31 follow.

	Three months ended March 31,
	2018		2017
	(In thousands)
IDR payments	$	2,128	$	2,100

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.

COMMITMENTS AND CONTINGENCIES - Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Rent expense	$ 1,022	$ 688

REVENUE - Narrative (Details) $ in Millions	3 Months Ended
REVENUE - Narrative (Details) $ in Millions	Mar. 31, 2018 USD ($)
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	$ 63.4
Contract assets included in accounts receivable	3.4
Gathering Services and Related Fees
Revenue From Contract With Customer [Line Items]
Contract liabilities, revenue	$ 1.1
Maximum
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, Period	25 years

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 3,366		$ 1,430	$ 6,285	$ 7,428
Accounts receivable	68,811		72,301
Other current assets	3,535		4,327
Due from affiliate	0		0
Total current assets	75,712		78,058
Property, plant and equipment, net	1,858,312	$ 1,828,252	1,795,129
Intangible assets, net	293,771		301,345
Goodwill	16,211		16,211
Investment in equity method investees	682,227		690,485
Other noncurrent assets	13,153		13,565
Investment in subsidiaries	0		0
Total assets	2,939,386		2,894,793
Liabilities and Partners' Capital
Trade accounts payable	21,232		16,375
Accrued expenses	13,971		12,499
Due to affiliate	443		1,088
Deferred revenue	10,159	10,088	4,000
Ad valorem taxes payable	3,834		8,329
Accrued interest	15,383		12,310
Accrued environmental remediation	3,068		3,130
Other current liabilities	5,984		11,258
Total current liabilities	74,074		68,989
Long-term debt	1,091,602		1,051,192
Deferred Purchase Price Obligation	384,617		362,959
Noncurrent deferred revenue	36,587	$ 35,528	12,707
Noncurrent accrued environmental remediation	1,916		2,214
Other noncurrent liabilities	6,509		7,063
Total liabilities	1,595,305		1,505,124
Total partners' capital	1,344,081		1,389,669	1,125,115	1,169,673
Total liabilities and partners' capital	2,939,386		2,894,793
Consolidating adjustments
Assets
Cash and cash equivalents	0		0	0	0
Accounts receivable	0		0
Other current assets	0		0
Due from affiliate	(537,642)		(515,097)
Total current assets	(537,642)		(515,097)
Property, plant and equipment, net	0		0
Intangible assets, net	0		0
Goodwill	0		0
Investment in equity method investees	0		0
Other noncurrent assets	0		0
Investment in subsidiaries	(5,403,854)		(5,344,164)
Total assets	(5,941,496)		(5,859,261)
Liabilities and Partners' Capital
Trade accounts payable	0		0
Accrued expenses	0		0
Due to affiliate	(537,642)		(515,097)
Deferred revenue	0		0
Ad valorem taxes payable	0		0
Accrued interest	0		0
Accrued environmental remediation	0		0
Other current liabilities	0		0
Total current liabilities	(537,642)		(515,097)
Long-term debt	0		0
Deferred Purchase Price Obligation	0		0
Noncurrent deferred revenue	0		0
Noncurrent accrued environmental remediation	0		0
Other noncurrent liabilities	0		0
Total liabilities	(537,642)		(515,097)
Total partners' capital	(5,403,854)		(5,344,164)
Total liabilities and partners' capital	(5,941,496)		(5,859,261)
Summit Midstream Partners, LP \| Reportable Legal Entities
Assets
Cash and cash equivalents	213		126	3,180	698
Accounts receivable	22		22
Other current assets	1,194		1,188
Due from affiliate	0		0
Total current assets	1,429		1,336
Property, plant and equipment, net	4,063		4,206
Intangible assets, net	0		0
Goodwill	0		0
Investment in equity method investees	0		0
Other noncurrent assets	2,768		2,547
Investment in subsidiaries	2,041,996		2,019,700
Total assets	2,050,256		2,027,789
Liabilities and Partners' Capital
Trade accounts payable	56		209
Accrued expenses	940		928
Due to affiliate	314,554		263,935
Deferred revenue	0		0
Ad valorem taxes payable	5		0
Accrued interest	0		0
Accrued environmental remediation	0		0
Other current liabilities	2,314		6,395
Total current liabilities	317,869		271,467
Long-term debt	0		0
Deferred Purchase Price Obligation	384,617		362,959
Noncurrent deferred revenue	0		0
Noncurrent accrued environmental remediation	0		0
Other noncurrent liabilities	3,689		3,694
Total liabilities	706,175		638,120
Total partners' capital	1,344,081		1,389,669
Total liabilities and partners' capital	2,050,256		2,027,789
Co-Issuers \| Reportable Legal Entities
Assets
Cash and cash equivalents	368		75	5	51
Accounts receivable	0		0
Other current assets	0		0
Due from affiliate	0		0
Total current assets	368		75
Property, plant and equipment, net	0		0
Intangible assets, net	0		0
Goodwill	0		0
Investment in equity method investees	0		0
Other noncurrent assets	10,286		10,913
Investment in subsidiaries	3,361,858		3,324,464
Total assets	3,372,512		3,335,452
Liabilities and Partners' Capital
Trade accounts payable	0		0
Accrued expenses	0		0
Due to affiliate	223,531		252,250
Deferred revenue	0		0
Ad valorem taxes payable	0		0
Accrued interest	15,383		12,310
Accrued environmental remediation	0		0
Other current liabilities	0		0
Total current liabilities	238,914		264,560
Long-term debt	1,091,602		1,051,192
Deferred Purchase Price Obligation	0		0
Noncurrent deferred revenue	0		0
Noncurrent accrued environmental remediation	0		0
Other noncurrent liabilities	0		0
Total liabilities	1,330,516		1,315,752
Total partners' capital	2,041,996		2,019,700
Total liabilities and partners' capital	3,372,512		3,335,452
Guarantor Subsidiaries \| Reportable Legal Entities
Assets
Cash and cash equivalents	2,331		1,138	2,784	5,768
Accounts receivable	60,378		65,842
Other current assets	1,955		2,697
Due from affiliate	500,061		493,067
Total current assets	564,725		562,744
Property, plant and equipment, net	1,504,830		1,442,333
Intangible assets, net	271,504		278,958
Goodwill	16,211		16,211
Investment in equity method investees	0		0
Other noncurrent assets	99		105
Investment in subsidiaries	0		0
Total assets	2,357,369		2,300,351
Liabilities and Partners' Capital
Trade accounts payable	16,822		11,283
Accrued expenses	11,607		10,592
Due to affiliate	0		0
Deferred revenue	9,722		4,000
Ad valorem taxes payable	3,693		7,809
Accrued interest	0		0
Accrued environmental remediation	0		0
Other current liabilities	3,338		4,385
Total current liabilities	45,182		38,069
Long-term debt	0		0
Deferred Purchase Price Obligation	0		0
Noncurrent deferred revenue	34,775		12,707
Noncurrent accrued environmental remediation	0		0
Other noncurrent liabilities	2,744		3,293
Total liabilities	82,701		54,069
Total partners' capital	2,274,668		2,246,282
Total liabilities and partners' capital	2,357,369		2,300,351
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Assets
Cash and cash equivalents	454		91	$ 316	$ 911
Accounts receivable	8,411		6,437
Other current assets	386		442
Due from affiliate	37,581		22,030
Total current assets	46,832		29,000
Property, plant and equipment, net	349,419		348,590
Intangible assets, net	22,267		22,387
Goodwill	0		0
Investment in equity method investees	682,227		690,485
Other noncurrent assets	0		0
Investment in subsidiaries	0		0
Total assets	1,100,745		1,090,462
Liabilities and Partners' Capital
Trade accounts payable	4,354		4,883
Accrued expenses	1,424		979
Due to affiliate	0		0
Deferred revenue	437		0
Ad valorem taxes payable	136		520
Accrued interest	0		0
Accrued environmental remediation	3,068		3,130
Other current liabilities	332		478
Total current liabilities	9,751		9,990
Long-term debt	0		0
Deferred Purchase Price Obligation	0		0
Noncurrent deferred revenue	1,812		0
Noncurrent accrued environmental remediation	1,916		2,214
Other noncurrent liabilities	76		76
Total liabilities	13,555		12,280
Total partners' capital	1,087,190		1,078,182
Total liabilities and partners' capital	$ 1,100,745		$ 1,090,462

GOODWILL

3 Months Ended

Mar. 31, 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. There have been no impairments of goodwill during the three months ended March 31, 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.

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Gathering services and related fees	$ 84,361	$ 118,013
Natural gas, NGLs and condensate sales	26,117	11,120
Other revenues	6,842	6,672
Total revenues	117,320	135,805
Costs and expenses:
Cost of natural gas and NGLs	20,286	9,052
Operation and maintenance	24,604	23,692
General and administrative	14,385	14,132
Depreciation and amortization	26,677	28,569
Transaction costs	57	0
(Gain) loss on asset sales, net	(74)	3
Long-lived asset impairment	0	284
Total costs and expenses	85,935	75,732
Other (expense) income	(7)	71
Interest expense	(15,122)	(16,716)
Early extinguishment of debt	0	(22,020)
Deferred Purchase Price Obligation	(21,658)	(20,883)
(Loss) income before income taxes and income (loss) from equity method investees	(5,402)	525
Income tax benefit (expense)	171	(452)
Income (loss) from equity method investees	1,386	(656)
Equity in earnings of consolidated subsidiaries	0	0
Net loss	(3,845)	(583)
Consolidating adjustments
Revenues:
Gathering services and related fees	0	0
Natural gas, NGLs and condensate sales	0	0
Other revenues	0	0
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	0	0
Operation and maintenance	0	0
General and administrative	0	0
Depreciation and amortization	0	0
Transaction costs	0
(Gain) loss on asset sales, net	0	0
Long-lived asset impairment		0
Total costs and expenses	0	0
Other (expense) income	0	0
Interest expense	0	0
Early extinguishment of debt		0
Deferred Purchase Price Obligation	0	0
(Loss) income before income taxes and income (loss) from equity method investees	0	0
Income tax benefit (expense)	0	0
Income (loss) from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	(51,398)	(80,406)
Net loss	(51,398)	(80,406)
Summit Midstream Partners, LP \| Reportable Legal Entities
Revenues:
Gathering services and related fees	0	0
Natural gas, NGLs and condensate sales	0	0
Other revenues	0	0
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	0	0
Operation and maintenance	0	0
General and administrative	0	0
Depreciation and amortization	432	154
Transaction costs	57
(Gain) loss on asset sales, net	0	0
Long-lived asset impairment		0
Total costs and expenses	489	154
Other (expense) income	(7)	71
Interest expense	0	0
Early extinguishment of debt		0
Deferred Purchase Price Obligation	(21,658)	(20,883)
(Loss) income before income taxes and income (loss) from equity method investees	(22,154)	(20,966)
Income tax benefit (expense)	171	(452)
Income (loss) from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	18,138	20,835
Net loss	(3,845)	(583)
Co-Issuers \| Reportable Legal Entities
Revenues:
Gathering services and related fees	0	0
Natural gas, NGLs and condensate sales	0	0
Other revenues	0	0
Total revenues	0	0
Costs and expenses:
Cost of natural gas and NGLs	0	0
Operation and maintenance	0	0
General and administrative	0	0
Depreciation and amortization	0	0
Transaction costs	0
(Gain) loss on asset sales, net	0	0
Long-lived asset impairment		0
Total costs and expenses	0	0
Other (expense) income	0	0
Interest expense	(15,122)	(16,716)
Early extinguishment of debt		(22,020)
Deferred Purchase Price Obligation	0	0
(Loss) income before income taxes and income (loss) from equity method investees	(15,122)	(38,736)
Income tax benefit (expense)	0	0
Income (loss) from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	33,260	59,571
Net loss	18,138	20,835
Guarantor Subsidiaries \| Reportable Legal Entities
Revenues:
Gathering services and related fees	69,466	102,513
Natural gas, NGLs and condensate sales	26,117	11,120
Other revenues	6,727	6,600
Total revenues	102,310	120,233
Costs and expenses:
Cost of natural gas and NGLs	20,286	9,052
Operation and maintenance	22,153	22,020
General and administrative	12,287	12,485
Depreciation and amortization	22,861	25,242
Transaction costs	0
(Gain) loss on asset sales, net	(74)	3
Long-lived asset impairment		0
Total costs and expenses	77,513	68,802
Other (expense) income	0	0
Interest expense	0	0
Early extinguishment of debt		0
Deferred Purchase Price Obligation	0	0
(Loss) income before income taxes and income (loss) from equity method investees	24,797	51,431
Income tax benefit (expense)	0	0
Income (loss) from equity method investees	0	0
Equity in earnings of consolidated subsidiaries	0	0
Net loss	24,797	51,431
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Revenues:
Gathering services and related fees	14,895	15,500
Natural gas, NGLs and condensate sales	0	0
Other revenues	115	72
Total revenues	15,010	15,572
Costs and expenses:
Cost of natural gas and NGLs	0	0
Operation and maintenance	2,451	1,672
General and administrative	2,098	1,647
Depreciation and amortization	3,384	3,173
Transaction costs	0
(Gain) loss on asset sales, net	0	0
Long-lived asset impairment		284
Total costs and expenses	7,933	6,776
Other (expense) income	0	0
Interest expense	0	0
Early extinguishment of debt		0
Deferred Purchase Price Obligation	0	0
(Loss) income before income taxes and income (loss) from equity method investees	7,077	8,796
Income tax benefit (expense)	0	0
Income (loss) from equity method investees	1,386	(656)
Equity in earnings of consolidated subsidiaries	0	0
Net loss	$ 8,463	$ 8,140

UNIT-BASED AND NONCASH COMPENSATION - Narrative (Details) - SMLP LTIP	1 Months Ended
	Mar. 31, 2018 $ / shares shares
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) \| $ / shares	$ 15.25
Vesting period (years)	3 years
Units vested (in shares)	328,388

RELATED-PARTY TRANSACTIONS

3 Months Ended

Mar. 31, 2018

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 March 31,
	2018		2017
	(In thousands)
Operation and maintenance expense	$	7,623	$	6,881
General and administrative expense		8,117		8,295

EQUITY METHOD INVESTMENTS

3 Months Ended

Mar. 31, 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.

A reconciliation of our 40% ownership interest in Ohio Gathering to our investment per Ohio Gathering's books and records follows (in thousands).

Investment in equity method investees, March 31, 2018	$	682,227
March cash distributions		2,568
Basis difference		(126,846	)
Investment in equity method investees, net of basis difference, February 28, 2018	$	557,949

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

	Three months ended February 28, 2018				Three months ended February 28, 2017
	OGC		OCC		OGC		OCC
	(In thousands)
Total revenues	$	34,960	$	2,489	$	37,075	$	2,053
Total operating expenses		26,775		2,141		27,105		2,473
Net income (loss)		8,180		180		7,973		(1,215	)

PARTNERS' CAPITAL - Narrative (Details) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
	Apr. 26, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) Transaction $ / shares shares	Mar. 31, 2017 $ / shares	Dec. 31, 2017 USD ($) $ / shares shares
Partners Capital [Line Items]
Preferred units issued \| shares		300,000		300,000
Per-unit annual distributions to unitholders (in dollars per unit)		$ 0.575	$ 0.575
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	May 15, 2018
Cash distribution date of record	May 08, 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 \| $				$ 150.0
Amount of stock sold (in shares) \| shares		0
Aggregate offering price \| $		$ 132.3
Transactions under ATM Program \| Transaction		0
General Partner
Partners Capital [Line Items]
Percentage interest in distributions (maximum)		50.00%

SEGMENT INFORMATION - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting [Abstract]
(Loss) income before income taxes and income (loss) from equity method investees	$ (5,402,000)	$ 525,000
Add:
Corporate and Other	10,623,000	10,093,000
Interest expense	15,122,000	16,716,000
Early extinguishment of debt	0	22,020,000
Deferred Purchase Price Obligation	21,658,000	20,883,000
Depreciation and amortization	26,526,000	28,418,000
Proportional adjusted EBITDA for equity method investees	10,477,000	9,073,000
Adjustments related to MVC shortfall payments	0	(28,640,000)
Adjustments related to capital reimbursement activity	40,000	0
Unit-based and noncash compensation	1,962,000	2,128,000
(Gain) loss on asset sales, net	(74,000)	3,000
Long-lived asset impairment	0	284,000
Total of reportable segments' measures of profit or loss	$ 80,932,000	$ 81,503,000

COMMITMENTS AND CONTINGENCIES (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2018		2017
	(In thousands)
Rent expense	$	1,022	$	688

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		(360	)
Accrued environmental remediation, March 31, 2018	$	4,984

DEBT (Tables)

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Schedule of debt and capital leases

Debt consisted of the following:

	March 31, 2018			December 31, 2017
	(In thousands)
Summit Holdings variable rate senior secured Revolving Credit Facility (3.90% at March 31, 2018 and 4.07% at December 31, 2017) due May 2022	$	301,000		$	261,000
Summit Holdings 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(2,747	)		(2,910	)
Summit Holdings 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(6,651	)		(6,898	)
Total long-term debt	$	1,091,602		$	1,051,192

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

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

+ Details

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2017	Mar. 31, 2018	Dec. 31, 2015
Maximum \| Meadowlark Midstream Gathering System \| Principal Owner
Loss Contingencies [Line Items]
Coverage from pollution liability insurance policy		$ 25,000,000.0	$ 25,000,000.0
Coverage from property and business interruption insurance policy		$ 200,000,000.0
Business Interruption
Loss Contingencies [Line Items]
Recoveries recognized	$ 2,600,000
Property Recoveries
Loss Contingencies [Line Items]
Recoveries recognized	$ 400,000

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Dec. 31, 2017	Feb. 29, 2016	Mar. 31, 2018	Jun. 30, 2016
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)	73,085,996		73,355,775
Summit Midstream Niobrara, LLC \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
Cost method ownership interest	1.00%
Purchase of Niobrara interest from Summit Epping LLC	$ 0.8
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%

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 30, 2018
Entity Information [Line Items]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	SMLP
Common units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		73,355,775
General Partner Units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,490,999

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT (Tables)

3 Months Ended

Mar. 31, 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.

	March 31, 2018
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(12,739	)	$	11,456
Contract intangibles		278,448		(124,356	)		154,092
Rights-of-way		160,931		(32,708	)		128,223
Total intangible assets	$	463,574	$	(169,803	)	$	293,771

Unfavorable gas gathering contract	$	10,962	$	(9,613	)	$	1,349

	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 March 31,
	2018			2017
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(389	)	$	(389	)
Amortization expense – unfavorable gas gathering contract		540			540

We recognized amortization expense in costs and expenses as follows:

	Three months ended March 31,
	2018		2017
	(In thousands)
Amortization expense – contract intangibles	$	6,535	$	8,551
Amortization expense – rights-of-way		1,585		1,527

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	$	25,544	$	1,349
2019		33,171		—
2020		32,995		—
2021		29,303		—
2022		26,236		—

UNIT-BASED AND NONCASH COMPENSATION

3 Months Ended

Mar. 31, 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 period.

•

Also in March 2018, 328,388 phantom units vested.

•

As of March 31, 2018, approximately 3.2 million common units remained available for future issuance under the SMLP LTIP.

PARTNERS' CAPITAL - Cash Distributions Paid and Declared (Details) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Per-unit annual distributions to unitholders (in dollars per unit)	$ 0.575	$ 0.575

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Mar. 31, 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

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

3 Months Ended

Mar. 31, 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 2% general partner interest in SMLP (including the IDRs), Summit Investments has indirect ownership interests in our common units. As of March 31, 2018, Summit Investments beneficially owned 25,854,581 SMLP common units and a subsidiary of Energy Capital Partners directly owned 5,915,827 SMLP common units.

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 and 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 under development in the northern Delaware Basin 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) 100% of the issued and outstanding membership interests of Summit Utica, Meadowlark Midstream and Tioga Midstream and collectively with Summit Utica and Meadowlark Midstream, (the "Contributed Entities"), each a limited liability company and (ii) a 40% ownership interest in each of OGC and OCC (collectively with OpCo and the Contributed Entities, the “2016 Drop Down Assets”)(the “2016 Drop Down”). The 2016 Drop Down closed in March 2016; concurrent therewith, a subsidiary of Summit Investments retained a 1% noncontrolling interest in OpCo.

In December 2017, the Niobrara 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 for approximately $0.8 million; 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, a Delaware limited liability company and a wholly owned subsidiary of Summit Holdings, manages OpCo, a Delaware limited liability partnership, and 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 March 31, 2018, the unaudited condensed consolidated statements of operations, partners’ capital and cash flows for the three months ended March 31, 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. 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.

RELATED-PARTY TRANSACTIONS (Tables)

3 Months Ended

Mar. 31, 2018

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 March 31,
	2018		2017
	(In thousands)
Operation and maintenance expense	$	7,623	$	6,881
General and administrative expense		8,117		8,295

SUBSEQUENT EVENTS

3 Months Ended

Mar. 31, 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 April 2018, we received information from a key customer on our Utica Shale segment and a new customer on our Williston Basin segment. The impact of this new information would result in an increase to the calculation of the undiscounted value of the Deferred Purchase Price Obligation of approximately $49.6 million, from $467.5 million to $517.1 million.

DEFERRED REVENUE (Tables)

3 Months Ended

Mar. 31, 2018

Deferred Revenue Disclosure [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		5		325		5,344		400		9		6,083
Less revenue recognized		5		254		5,344		400		9		6,012
Current deferred revenue, March 31, 2018	$	18	$	1,088	$	7,396	$	1,619	$	38	$	10,159

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		—		—		2,833		724		—		3,557
Less reclassification to current deferred revenue		5		254		1,830		400		9		2,498
Noncurrent deferred revenue, March 31, 2018	$	34	$	3,961	$	23,727	$	8,541	$	324	$	36,587

FINANCIAL INSTRUMENTS

3 Months Ended

Mar. 31, 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 five customers or counterparties accounted for 47% of total accounts receivable at March 31, 2018, compared with 44% as of December 31, 2017.

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 non-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		21,658
Level 3 liability, March 31, 2018	$	384,617

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

	March 31, 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)	$	297,253	$	292,250	$	297,090	$	301,750
Summit Holdings 5.75% Senior Notes ($500.0 million principal)		493,349		475,000		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 March 31, 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.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Accounting Pronouncements

Recently Adopted Accounting Pronouncements. We have recently adopted the following accounting pronouncements:

•

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

	March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Assets
Accounts receivable	$	68,811	$	66,386	$	2,425
Property, plant and equipment, net		1,858,312		1,824,484		33,828

Liabilities
Deferred revenue, current		10,159		4,071		6,088
Deferred revenue, noncurrent		36,587		12,707		23,880

Partners' Capital (1)		1,032,442		1,026,157		6,285

________

(1) Includes common limited partner capital and general partner interests.

Unaudited condensed consolidated statement of operations

	Three months ended March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Revenues
Gathering services and related fees	$	84,361	$	85,303	$	(942	)
Costs and expenses
Cost of natural gas and NGLs		20,286		23,602		(3,316	)
Depreciation and amortization		26,677		26,374		303

Unaudited condensed consolidated statement of cash flows

	Three months ended March 31, 2018
	As Reported			Balances Without Adoption of Topic 606			Effect of Change Increase / (Decrease)
	(In thousands)
Cash flows from operating activities:
Net loss	$	(3,845	)	$	(5,916	)	$	2,071
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization		26,526			26,223			303
Cash flows from operating activities:
Accounts receivable		3,490			5,915			(2,425	)
Deferred revenue, net		1,130			1,079			51

•

Accounting Pronouncements Pending Adoption. We have not yet adopted the following accounting pronouncements as of March 31, 2018:

•

Basis of Presentation

DEBT

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

DEBT

10. DEBT

Debt consisted of the following:

	March 31, 2018			December 31, 2017
	(In thousands)
Summit Holdings variable rate senior secured Revolving Credit Facility (3.90% at March 31, 2018 and 4.07% at December 31, 2017) due May 2022	$	301,000		$	261,000
Summit Holdings 5.5% senior unsecured notes due August 2022		300,000			300,000
Less unamortized debt issuance costs (1)		(2,747	)		(2,910	)
Summit Holdings 5.75% senior unsecured notes due April 2025		500,000			500,000
Less unamortized debt issuance costs (1)		(6,651	)		(6,898	)
Total long-term debt	$	1,091,602		$	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.

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 March 31, 2018, the applicable margin under LIBOR borrowings was 2.25%, the interest rate was 3.90% and the unused portion of the Revolving Credit Facility totaled $949.0 million (subject to a commitment fee of 0.375%).

As of March 31, 2018, we had $10.3 million of debt issuance costs attributable to our Revolving Credit Facility and related amendments which are included in noncurrent assets on the unaudited condensed consolidated balance sheet.

As of and during the three months ended March 31, 2018, we were in compliance with the Revolving Credit Facility's covenants. There were no defaults or events of default during the three months ended March 31, 2018.

Senior Notes. In June 2013, Summit Holdings and its 100% owned finance subsidiary, Finance Corp. (together with Summit Holdings, the "Co-Issuers") co-issued $300.0 million of 7.5% senior unsecured notes (the "7.5% Senior Notes"). In July 2014, 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 $500.0 million of 5.75% senior unsecured notes (the "5.75% Senior Notes") as described in the 2017 Annual Report. Concurrent with the 5.75% Senior Notes offering, we made a tender offer to purchase all the outstanding 7.5% Senior Notes. References to the “Senior Notes,” when used for dates or periods ended on or after the date of issuance of the 5.75% Senior Notes but before the redemption date, refer collectively to 5.5% Senior Notes, 7.5% Senior Notes and 5.75% Senior Notes. References to the "Senior Notes," when used for dates or periods ended on or prior to the date of issuance of the 5.75% Senior Notes, refer collectively to 5.5% Senior Notes and 7.5% Senior Notes. References to the "Senior Notes," when used for dates or periods that ended after the redemption date, refer collectively to the 5.5% Senior Notes and the 5.75% Senior Notes.

In 2017, we executed supplemental indentures and amendments to our Revolving Credit Facility to add three newly formed entities, Summit Permian, Permian Finance and Summit Niobrara, as guarantors. As a result, 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 three months ended March 31, 2018, we were in compliance with the covenants governing our Senior Notes. There were no defaults or events of default during the three months ended March 31, 2018.

COMMITMENTS AND CONTINGENCIES

3 Months Ended

Mar. 31, 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 March 31,
	2018		2017
	(In thousands)
Rent expense	$	1,022	$	688

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.

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 $25.0 million from its pollution liability insurance policy and $200.0 million from its property and business interruption insurance policy. Summit Investments exhausted the $25.0 million pollution liability policy in 2015. We submitted property and business interruption claim requests to the insurers and reached a settlement in January 2017. In connection therewith, we recognized $2.6 million of business interruption recoveries and $0.4 million of property recoveries.

A rollforward of the aggregate accrued environmental remediation liabilities follows.

	Total
	(In thousands)
Accrued environmental remediation, January 1, 2018	$	5,344
Payments made		(360	)
Accrued environmental remediation, March 31, 2018	$	4,984

As of March 31, 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 March 31, 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.

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.

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Gathering services and related fees	$ 84,361	$ 118,013
Natural gas, NGLs and condensate sales	26,117	11,120
Other revenues	6,842	6,672
Total revenues	117,320	135,805
Costs and expenses:
Cost of natural gas and NGLs	20,286	9,052
Operation and maintenance	24,604	23,692
General and administrative	14,385	14,132
Depreciation and amortization	26,677	28,569
Transaction costs	57	0
(Gain) loss on asset sales, net	(74)	3
Long-lived asset impairment	0	284
Total costs and expenses	85,935	75,732
Other (expense) income	(7)	71
Interest expense	(15,122)	(16,716)
Early extinguishment of debt	0	(22,020)
Deferred Purchase Price Obligation	(21,658)	(20,883)
(Loss) income before income taxes and income (loss) from equity method investees	(5,402)	525
Income tax benefit (expense)	171	(452)
Income (loss) from equity method investees	1,386	(656)
Net loss	(3,845)	(583)
Net income attributable to noncontrolling interest	85	102
Net loss attributable to SMLP	(3,930)	(685)
Less net income attributable to General Partner, including IDRs	2,058	2,092
Net income (loss) attributable to limited partners	(5,988)	(2,777)
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners	7,125	0
Common units
Costs and expenses:
Net income (loss) attributable to limited partners	$ (13,113)	$ (2,777)
Loss per limited partner unit:
Basic (in dollars per share)	$ (0.18)	$ (0.04)
Diluted (in dollars per share)	$ (0.18)	$ (0.04)
Weighted-average limited partner units outstanding:
Basic (shares)	73,134	72,149
Diluted (shares)	73,134	72,149

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Depreciation Expense and Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 18,557	$ 18,491
Capitalized interest	$ 1,222	$ 468

PARTNERS' CAPITAL - Partners' Capital and Schedule of Units (Details)	3 Months Ended
	Mar. 31, 2018 shares
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

DEBT - Senior Notes (Narrative) (Details) - USD ($)		1 Months Ended
DEBT - Senior Notes (Narrative) (Details) - USD ($)	Jul. 31, 2014	Jun. 30, 2013	Feb. 08, 2017
5.75% Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%		5.75%
Debt face amount			$ 500,000,000.0
Summit Holdings and Finance Corporation \| 7.5% Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes		$ 300,000,000.0
Stated interest rate		7.50%
Summit Holdings and Finance Corporation \| Senior Notes Due August 2022
Debt Instrument [Line Items]
Senior unsecured notes	$ 300,000,000.0
Stated interest rate	5.50%
Maturity date	Aug. 15, 2022
Finance Corp \| Summit Holdings
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary		100.00%

EARNINGS PER UNIT

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

EARNINGS PER UNIT

13. EARNINGS PER UNIT

The following table details the components of EPU.

	Three months ended March 31,
	2018			2017
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net loss among limited partner interests:
Net loss attributable to limited partners	$	(5,988	)	$	(2,777	)
Less net income attributable to Series A Preferred Units		7,125			—
Net loss attributable to common limited partners	$	(13,113	)	$	(2,777	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic		73,134			72,149
Effect of nonvested phantom units		—			—
Weighted-average common units outstanding – diluted		73,134			72,149

Loss per limited partner unit:
Common unit – basic	$	(0.18	)	$	(0.04	)
Common unit – diluted	$	(0.18	)	$	(0.04	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		4			167

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
	Mar. 31, 2018	Mar. 31, 2017
Other Revenue \| Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (389)	$ (389)
Other Revenue \| Unfavorable Gas Gathering Contract
Finite-Lived Intangible Assets [Line Items]
Amortization expense	540	540
Costs And Expenses \| Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,535	8,551
Costs And Expenses \| Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,585	$ 1,527

REVENUE (Tables)

3 Months Ended

Mar. 31, 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	$	115,834	$	133,743	$	122,429	$	102,777	$	83,648	$	174,227

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 March 31, 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	$	10,041	$	17,666	$	35,294	$	13,637	$	7,825	$	84,463	$	(102	)	$	84,361
Natural gas, NGLs and condensate sales		—		7,846		4,325		545		—		12,716		13,401			26,117
Other revenues		—		2,912		1,968		1,988		—		6,868		(26	)		6,842
Total	$	10,041	$	28,424	$	41,587	$	16,170	$	7,825	$	104,047	$	13,273		$	117,320

REVENUE

3 Months Ended

Mar. 31, 2018

Revenue From Contract With Customer [Abstract]

REVENUE

3. REVENUE

The majority of our revenue is derived from long-term and 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 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 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 will 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 picked up 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 picked up 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 or annual 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.

	2018		2019		2020		2021		2022		Thereafter
	(In thousands)
Gathering services and related fees	$	115,834	$	133,743	$	122,429	$	102,777	$	83,648	$	174,227

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 March 31, 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	$	10,041	$	17,666	$	35,294	$	13,637	$	7,825	$	84,463	$	(102	)	$	84,361
Natural gas, NGLs and condensate sales		—		7,846		4,325		545		—		12,716		13,401			26,117
Other revenues		—		2,912		1,968		1,988		—		6,868		(26	)		6,842
Total	$	10,041	$	28,424	$	41,587	$	16,170	$	7,825	$	104,047	$	13,273		$	117,320

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. As of March 31, 2018, receivables with customers totaled $63.4 million and contract assets totaled $3.4 million which were included in the accounts receivable 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 months ended March 31, 2018, we recognized $1.1 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.

PROPERTY, PLANT, AND EQUIPMENT, NET

3 Months Ended

Mar. 31, 2018

Property Plant And Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT, NET

5. PROPERTY, PLANT AND EQUIPMENT, NET

Details on property, plant and equipment follow.

	March 31, 2018		December 31, 2017
	(In thousands)
Gathering and processing systems and related equipment	$	2,014,522	$	1,973,722
Construction in progress		122,132		78,850
Land and line fill		11,735		11,735
Other		41,114		40,262
Total		2,189,503		2,104,569
Less accumulated depreciation		331,191		309,440
Property, plant and equipment, net	$	1,858,312	$	1,795,129

Depreciation expense and capitalized interest follow.

	Three months ended March 31,
	2018		2017
	(In thousands)
Depreciation expense	$	18,557	$	18,491
Capitalized interest		1,222		468

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT - Intangible Assets and Liabilities Subject to Amortization (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 463,574	$ 462,629
Accumulated amortization	(169,803)	(161,284)
Net	293,771	301,345
Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24,195	24,195
Accumulated amortization	(12,739)	(12,350)
Net	11,456	11,845
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	278,448	278,448
Accumulated amortization	(124,356)	(117,821)
Net	154,092	160,627
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	160,931	159,986
Accumulated amortization	(32,708)	(31,113)
Net	128,223	128,873
Unfavorable Gas Gathering Contract
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	10,962	10,962
Accumulated amortization	(9,613)	(9,074)
Net	$ 1,349	$ 1,888

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
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Gathering services and related fees	$ 84,361	$ 118,013
Costs and expenses:
Cost of natural gas and NGLs	20,286	9,052
Depreciation and amortization	26,677	$ 28,569
Balances Without Adoption of Topic 606
Revenues:
Gathering services and related fees	85,303
Costs and expenses:
Cost of natural gas and NGLs	23,602
Depreciation and amortization	26,374
Accounting Standard Update 2014-09 \| Effect of Change Increase / (Decrease)
Revenues:
Gathering services and related fees	(942)
Costs and expenses:
Cost of natural gas and NGLs	(3,316)
Depreciation and amortization	$ 303

SEGMENT INFORMATION (Tables)

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Schedule of assets by reportable segment

Assets by reportable segment follow.

	March 31, 2018			December 31, 2017
	(In thousands)
Assets:
Utica Shale	$	211,058		$	212,311
Ohio Gathering		682,227			690,485
Williston Basin		515,701			512,860
Piceance/DJ Basins		829,571			798,722
Barnett Shale		379,360			383,306
Marcellus Shale		215,587			217,362
Total reportable segment assets		2,833,504			2,815,046
Corporate and Other		106,268			79,996
Eliminations		(386	)		(249	)
Total assets	$	2,939,386		$	2,894,793

Schedule of segment reporting information

Revenues by reportable segment follow.

	Three months ended March 31,
	2018			2017
	(In thousands)
Revenues (1):
Utica Shale	$	10,041		$	8,796
Williston Basin		28,424			66,885
Piceance/DJ Basins		41,587			34,808
Barnett Shale		16,170			17,742
Marcellus Shale		7,825			6,904
Total reportable segments revenue		104,047			135,135
Corporate and Other		14,176			1,786
Eliminations		(903	)		(1,116	)
Total revenues	$	117,320		$	135,805

(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 March 31,
	2018		2017
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	1,853	$	1,647
Williston Basin		5,609		8,381
Piceance/DJ Basins		12,555		12,211
Barnett Shale (2)		3,757		3,762
Marcellus Shale		2,272		2,263
Total reportable segment depreciation and amortization		26,046		28,264
Corporate and Other		480		154
Total depreciation and amortization	$	26,526	$	28,418

(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.

	Three months ended March 31,
	2018		2017
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	1,020	$	7,862
Williston Basin		5,888		429
Piceance/DJ Basins		16,904		5,864
Barnett Shale		37		(995	)
Marcellus Shale		487		265
Total reportable segment capital expenditures		24,336		13,425
Corporate and Other		16,442		1,003
Total cash paid for capital expenditures	$	40,778	$	14,428

(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 March 31,
	2018			2017
Percentage of total revenues (1)(2):
Counterparty A - Piceance/DJ Basins		11	%	*
Counterparty B - Williston Basin	*				32	%

(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 March 31,
	2018		2017
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	8,715	$	7,912
Ohio Gathering		10,477		9,073
Williston Basin		15,970		17,809
Piceance/DJ Basins		29,235		28,974
Barnett Shale		9,859		12,088
Marcellus Shale		6,676		5,647
Total of reportable segments' measures of profit or loss	$	80,932	$	81,503

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

	Three months ended March 31,
	2018			2017
	(In thousands)
Reconciliation of (loss) income before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit or loss:
(Loss) income before income taxes and income (loss) from equity method investees	$	(5,402	)	$	525
Add:
Corporate and Other		10,623			10,093
Interest expense		15,122			16,716
Early extinguishment of debt		—			22,020
Deferred Purchase Price Obligation		21,658			20,883
Depreciation and amortization		26,526			28,418
Proportional adjusted EBITDA for equity method investees		10,477			9,073
Adjustments related to MVC shortfall payments		—			(28,640	)
Adjustments related to capital reimbursement activity		40			—
Unit-based and noncash compensation		1,962			2,128
(Gain) loss on asset sales, net		(74	)		3
Long-lived asset impairment		—			284
Total of reportable segments' measures of profit or loss	$	80,932		$	81,503

Schedule of Adjustments Related to Minimum Volume Commitments Shortfall Payments

Adjustments related to MVC shortfall payments by reportable segment for the three months ended March 31, 2017 follow. There were no adjustments related to MVC shortfall payments for the three months ended March 31, 2018.

	Three months ended March 31, 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	)	$	(792	)	$	—	$	(38,485	)
Expected MVC shortfall adjustments		1,982			6,545			1,318		9,845
Total adjustments related to MVC shortfall payments	$	(35,711	)	$	5,753		$	1,318	$	(28,640	)

PROPERTY, PLANT, AND EQUIPMENT, NET - Schedule of Property, Plant, and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,189,503		$ 2,104,569
Less accumulated depreciation	331,191		309,440
Property, plant and equipment, net	1,858,312	$ 1,828,252	1,795,129
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,014,522		1,973,722
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	122,132		78,850
Land and line fill
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,735		11,735
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 41,114		$ 40,262

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

3 Months Ended

Mar. 31, 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 statement of operations

	Three months ended March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Revenues
Gathering services and related fees	$	84,361	$	85,303	$	(942	)
Costs and expenses
Cost of natural gas and NGLs		20,286		23,602		(3,316	)
Depreciation and amortization		26,677		26,374		303

Unaudited condensed consolidated statement of cash flows

	Three months ended March 31, 2018
	As Reported			Balances Without Adoption of Topic 606			Effect of Change Increase / (Decrease)
	(In thousands)
Cash flows from operating activities:
Net loss	$	(3,845	)	$	(5,916	)	$	2,071
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization		26,526			26,223			303
Cash flows from operating activities:
Accounts receivable		3,490			5,915			(2,425	)
Deferred revenue, net		1,130			1,079			51

Unaudited condensed consolidated balance sheet

	March 31, 2018
	As Reported		Balances Without Adoption of Topic 606		Effect of Change Increase / (Decrease)
	(In thousands)
Assets
Accounts receivable	$	68,811	$	66,386	$	2,425
Property, plant and equipment, net		1,858,312		1,824,484		33,828

Liabilities
Deferred revenue, current		10,159		4,071		6,088
Deferred revenue, noncurrent		36,587		12,707		23,880

Partners' Capital (1)		1,032,442		1,026,157		6,285

________

(1) Includes common limited partner capital and general partner interests.

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (3,845)	$ (583)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	26,526	28,418
Amortization of debt issuance costs	1,040	1,032
Deferred Purchase Price Obligation	21,658	20,883
Unit-based and noncash compensation	1,962	2,128
(Income) loss from equity method investees	(1,386)	656
Distributions from equity method investees	9,644	8,944
(Gain) loss on asset sales, net	(74)	3
Long-lived asset impairment	0	284
Early extinguishment of debt	0	22,020
Changes in operating assets and liabilities:
Accounts receivable	3,490	43,695
Trade accounts payable	(3,294)	(4,042)
Accrued expenses	1,472	718
Due (to) from affiliate	(645)	228
Deferred revenue, net	1,130	(38,485)
Ad valorem taxes payable	(4,495)	(6,522)
Accrued interest	3,073	(11,780)
Accrued environmental remediation, net	(360)	(307)
Other, net	(4,686)	(4,841)
Net cash provided by operating activities	51,210	62,449
Cash flows from investing activities:
Capital expenditures	(40,778)	(14,428)
Contributions to equity method investees	0	(4,936)
Other, net	(221)	(361)
Net cash provided by (used in) investing activities	(40,999)	(19,725)
Cash flows from financing activities:
Distributions to unitholders	(45,053)	(44,452)
Borrowings under Revolving Credit Facility	50,000	72,000
Repayments under Revolving Credit Facility	(10,000)	(245,000)
Debt issuance costs	(4)	(6,825)
Payment of redemption and call premiums on senior notes	0	(17,913)
Proceeds from ATM Program common unit issuances, net of costs	0	367
Contribution from General Partner	0	113
Issuance of senior notes	0	500,000
Tender and redemption of senior notes	0	(300,000)
Other, net	(3,218)	(2,157)
Net cash provided by (used in) financing activities	(8,275)	(43,867)
Net change in cash and cash equivalents	1,936	(1,143)
Cash and cash equivalents, beginning of period	1,430	7,428
Cash and cash equivalents, end of period	3,366	6,285
Supplemental cash flow disclosures:
Cash interest paid	12,207	28,040
Less capitalized interest	1,222	468
Interest paid (net of capitalized interest)	10,985	27,572
Noncash investing and financing activities
Capital expenditures in trade accounts payable (period end accruals)	19,943	13,977
Capital expenditures relating to contributions in aid of construction for Topic 606 day 1 adoption	$ 33,123	$ 0

CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)

3 Months Ended

Mar. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Condensed Balance Sheet

Balance sheets as of March 31, 2018 and December 31, 2017 follow.

	March 31, 2018
	SMLP		Co-Issuers		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Assets
Cash and cash equivalents	$	213	$	368	$	2,331	$	454	$	—		$	3,366
Accounts receivable		22		—		60,378		8,411		—			68,811
Other current assets		1,194		—		1,955		386		—			3,535
Due from affiliate		—		—		500,061		37,581		(537,642	)		—
Total current assets		1,429		368		564,725		46,832		(537,642	)		75,712
Property, plant and equipment, net		4,063		—		1,504,830		349,419		—			1,858,312
Intangible assets, net		—		—		271,504		22,267		—			293,771
Goodwill		—		—		16,211		—		—			16,211
Investment in equity method investees		—		—		—		682,227		—			682,227
Other noncurrent assets		2,768		10,286		99		—		—			13,153
Investment in subsidiaries		2,041,996		3,361,858		—		—		(5,403,854	)		—
Total assets	$	2,050,256	$	3,372,512	$	2,357,369	$	1,100,745	$	(5,941,496	)	$	2,939,386

Liabilities and Partners' Capital
Trade accounts payable	$	56	$	—	$	16,822	$	4,354	$	—		$	21,232
Accrued expenses		940		—		11,607		1,424		—			13,971
Due to affiliate		314,554		223,531		—		—		(537,642	)		443
Deferred revenue		—		—		9,722		437		—			10,159
Ad valorem taxes payable		5		—		3,693		136		—			3,834
Accrued interest		—		15,383		—		—		—			15,383
Accrued environmental remediation		—		—		—		3,068		—			3,068
Other current liabilities		2,314		—		3,338		332		—			5,984
Total current liabilities		317,869		238,914		45,182		9,751		(537,642	)		74,074
Long-term debt		—		1,091,602		—		—		—			1,091,602
Deferred Purchase Price Obligation		384,617		—		—		—		—			384,617
Noncurrent deferred revenue		—		—		34,775		1,812		—			36,587
Noncurrent accrued environmental remediation		—		—		—		1,916		—			1,916
Other noncurrent liabilities		3,689		—		2,744		76		—			6,509
Total liabilities		706,175		1,330,516		82,701		13,555		(537,642	)		1,595,305

Total partners' capital		1,344,081		2,041,996		2,274,668		1,087,190		(5,403,854	)		1,344,081
Total liabilities and partners' capital	$	2,050,256	$	3,372,512	$	2,357,369	$	1,100,745	$	(5,941,496	)	$	2,939,386

	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
Noncurrent 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 months ended March 31, 2018 and 2017 follow.

	Three months ended March 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	69,466		$	14,895	$	—		$	84,361
Natural gas, NGLs and condensate sales		—			—			26,117			—		—			26,117
Other revenues		—			—			6,727			115		—			6,842
Total revenues		—			—			102,310			15,010		—			117,320
Costs and expenses:
Cost of natural gas and NGLs		—			—			20,286			—		—			20,286
Operation and maintenance		—			—			22,153			2,451		—			24,604
General and administrative		—			—			12,287			2,098		—			14,385
Depreciation and amortization		432			—			22,861			3,384		—			26,677
Transaction costs		57			—			—			—		—			57
Gain on asset sales, net		—			—			(74	)				—			(74	)
Total costs and expenses		489			—			77,513			7,933		—			85,935
Other expense		(7	)		—			—			—		—			(7	)
Interest expense		—			(15,122	)		—			—		—			(15,122	)
Deferred Purchase Price Obligation		(21,658	)		—			—			—		—			(21,658	)
(Loss) income before income taxes and income from equity method investees		(22,154	)		(15,122	)		24,797			7,077		—			(5,402	)
Income tax benefit		171			—			—			—		—			171
Income from equity method investees		—			—			—			1,386		—			1,386
Equity in earnings of consolidated subsidiaries		18,138			33,260			—			—		(51,398	)		—
Net (loss) income	$	(3,845	)	$	18,138		$	24,797		$	8,463	$	(51,398	)	$	(3,845	)

	Three months ended March 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Revenues:
Gathering services and related fees	$	—		$	—		$	102,513	$	15,500		$	—		$	118,013
Natural gas, NGLs and condensate sales		—			—			11,120		—			—			11,120
Other revenues		—			—			6,600		72			—			6,672
Total revenues		—			—			120,233		15,572			—			135,805
Costs and expenses:
Cost of natural gas and NGLs		—			—			9,052		—			—			9,052
Operation and maintenance		—			—			22,020		1,672			—			23,692
General and administrative		—			—			12,485		1,647			—			14,132
Depreciation and amortization		154			—			25,242		3,173			—			28,569
Loss on asset sales, net		—			—			3		—			—			3
Long-lived asset impairment		—			—			—		284			—			284
Total costs and expenses		154			—			68,802		6,776			—			75,732
Other income		71			—			—		—			—			71
Interest expense		—			(16,716	)		—		—			—			(16,716	)
Early extinguishment of debt		—			(22,020	)		—		—			—			(22,020	)
Deferred Purchase Price Obligation		(20,883	)		—			—		—			—			(20,883	)
(Loss) income before income taxes and loss from equity method investees		(20,966	)		(38,736	)		51,431		8,796			—			525
Income tax expense		(452	)		—			—		—			—			(452	)
Loss from equity method investees		—			—			—		(656	)		—			(656	)
Equity in earnings of consolidated subsidiaries		20,835			59,571			—		—			(80,406	)		—
Net (loss) income	$	(583	)	$	20,835		$	51,431	$	8,140		$	(80,406	)	$	(583	)

Condensed Cash Flow Statement

Statements of cash flows for the three months ended March 31, 2018 and 2017 follow.

	March 31, 2018
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$	(2,721	)	$	(10,985	)	$	47,495		$	17,421		$	—		$	51,210

Cash flows from investing activities:
Capital expenditures		(297	)		—			(39,001	)		(1,480	)		—			(40,778	)
Other, net		(221	)		—			—			—			—			(221	)
Advances to affiliates		—			(28,718	)		(6,995	)		(15,549	)		51,262			—
Net cash used in investing activities		(518	)		(28,718	)		(45,996	)		(17,029	)		51,262			(40,999	)

Cash flows from financing activities:
Distributions to unitholders		(45,053	)		—			—			—			—			(45,053	)
Borrowings under Revolving Credit Facility		—			50,000			—			—			—			50,000
Repayments under Revolving Credit Facility		—			(10,000	)		—			—			—			(10,000	)
Debt issuance costs		—			(4	)		—			—			—			(4	)
Other, net		(2,883	)		—			(306	)		(29	)		—			(3,218	)
Advances from affiliates		51,262			—			—			—			(51,262	)		—
Net cash provided by (used in) financing activities		3,326			39,996			(306	)		(29	)		(51,262	)		(8,275	)
Net change in cash and cash equivalents		87			293			1,193			363			—			1,936
Cash and cash equivalents, beginning of period		126			75			1,138			91			—			1,430
Cash and cash equivalents, end of period	$	213		$	368		$	2,331		$	454		$	—		$	3,366

	March 31, 2017
	SMLP			Co-Issuers			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating adjustments			Total
	(In thousands)
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$	(2,021	)	$	(27,574	)	$	75,271		$	16,773		$	—		$	62,449

Cash flows from investing activities:
Capital expenditures		(1,003	)		—			(6,089	)		(7,336	)		—			(14,428	)
Contributions to equity method investees		—			—			—			(4,936	)		—			(4,936	)
Other, net		(361	)		—			—			—			—			(361	)
Advances to affiliates		(20,185	)		—			(72,075	)		—			92,260			—
Net cash used in investing activities		(21,549	)		—			(78,164	)		(12,272	)		92,260			(19,725	)

Cash flows from financing activities:
Distributions to unitholders		(44,452	)		—			—			—			—			(44,452	)
Borrowings under Revolving Credit Facility		—			72,000			—			—			—			72,000
Repayments under Revolving Credit Facility		—			(245,000	)		—			—			—			(245,000	)
Debt issuance costs		—			(6,825	)		—			—			—			(6,825	)
Payment of redemption and call premiums on senior notes		—			(17,913	)		—			—			—			(17,913	)
Proceeds from ATM Program issuances, net of costs		367			—			—			—			—			367
Contribution from General Partner		113			—			—			—			—			113
Issuance of senior notes		—			500,000			—			—			—			500,000
Tender and redemption of senior notes		—			(300,000	)		—			—			—			(300,000	)
Other, net		(2,051	)		—			(91	)		(15	)		—			(2,157	)
Advances from affiliates		72,075			25,266			—			(5,081	)		(92,260	)		—
Net cash provided by (used in) financing activities		26,052			27,528			(91	)		(5,096	)		(92,260	)		(43,867	)
Net change in cash and cash equivalents		2,482			(46	)		(2,984	)		(595	)		—			(1,143	)
Cash and cash equivalents, beginning of period		698			51			5,768			911			—			7,428
Cash and cash equivalents, end of period	$	3,180		$	5		$	2,784		$	316		$	—		$	6,285

EQUITY METHOD INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Equity Method Investments And Joint Ventures [Abstract]

Equity Method Investments

A reconciliation of our 40% ownership interest in Ohio Gathering to our investment per Ohio Gathering's books and records follows (in thousands).

Investment in equity method investees, March 31, 2018	$	682,227
March cash distributions		2,568
Basis difference		(126,846	)
Investment in equity method investees, net of basis difference, February 28, 2018	$	557,949

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

	Three months ended February 28, 2018				Three months ended February 28, 2017
	OGC		OCC		OGC		OCC
	(In thousands)
Total revenues	$	34,960	$	2,489	$	37,075	$	2,053
Total operating expenses		26,775		2,141		27,105		2,473
Net income (loss)		8,180		180		7,973		(1,215	)

ACQUISITIONS AND DROP DOWN TRANSACTIONS - 2016 Drop Down (Details) - USD ($) $ in Thousands		1 Months Ended
	Mar. 03, 2016	Jun. 30, 2016	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Deferred purchase price obligation			$ 384,617	$ 362,959
Drop Down Assets 2016 Acquisition
Business Acquisition [Line Items]
Initial payment	$ 360,000
Working capital adjustment		$ 600
Estimated future payment obligation			467,500
Deferred purchase price obligation			$ 384,600
Discount rate			10.25%

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
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

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ (5,988)	$ (2,777)
Phantom Units
Loss per limited partner unit:
Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU (in shares)	4	167
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
Common units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss) attributable to limited partners	$ (13,113)	$ (2,777)
Weighted-average units outstanding (in shares)	73,134	72,149
Effect of nonvested phantom units (in shares)	0	0
Weighted-average units outstanding – diluted (shares)	73,134	72,149
Loss per limited partner unit:
Basic (in dollars per share)	$ (0.18)	$ (0.04)
Diluted (in dollars per share)	$ (0.18)	$ (0.04)

EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Equity Method Investment [Roll Forward]
Investment in equity method investees, March 31, 2018	$ 682,227	$ 682,227
March cash distributions		9,644	$ 8,944
Investment in equity method investees, net of basis difference, February 28, 2018		690,485
OGC \| Summit Midstream Partners, LLC
Equity Method Investment [Roll Forward]
Investment in equity method investees, March 31, 2018	682,227	$ 682,227
March cash distributions	2,568
Basis difference	(126,846)
Investment in equity method investees, net of basis difference, February 28, 2018	$ 557,949

PARTNERS' CAPITAL (Tables)

3 Months Ended

Mar. 31, 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, March 31, 2018		300,000		73,355,775		1,490,999

Details of cash distributions

We paid the following per-unit distributions during the three months ended March 31:

	Three months ended March 31,
	2018		2017
Per-unit distributions to unitholders	$	0.575	$	0.575

Our payment of IDRs as reported in distributions to unitholders – general partner in the statement of partners' capital during the three months ended March 31 follow.

	Three months ended March 31,
	2018		2017
	(In thousands)
IDR payments	$	2,128	$	2,100

SEGMENT INFORMATION - Assets, Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 2,939,386		$ 2,894,793
Revenues	117,320	$ 135,805
Depreciation and amortization	26,526	28,418
Capital expenditures	40,778	14,428
Corporate
Segment Reporting Information [Line Items]
Capital expenditures	300
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,833,504		2,815,046
Revenues	104,047	135,135
Depreciation and amortization	26,046	28,264
Capital expenditures	24,336	13,425
Reportable Segments \| Utica Shale
Segment Reporting Information [Line Items]
Assets	211,058		212,311
Revenues	10,041	8,796
Depreciation and amortization	1,853	1,647
Capital expenditures	1,020	7,862
Reportable Segments \| Ohio Gathering
Segment Reporting Information [Line Items]
Assets	682,227		690,485
Reportable Segments \| Williston Basin
Segment Reporting Information [Line Items]
Assets	515,701		512,860
Revenues	28,424	66,885
Depreciation and amortization	5,609	8,381
Capital expenditures	5,888	429
Reportable Segments \| Piceance/DJ Basins
Segment Reporting Information [Line Items]
Assets	829,571		798,722
Revenues	41,587	34,808
Depreciation and amortization	12,555	12,211
Capital expenditures	16,904	5,864
Reportable Segments \| Barnett Shale
Segment Reporting Information [Line Items]
Assets	379,360		383,306
Revenues	16,170	17,742
Depreciation and amortization	3,757	3,762
Capital expenditures	37	(995)
Reportable Segments \| Marcellus Shale
Segment Reporting Information [Line Items]
Assets	215,587		217,362
Revenues	7,825	6,904
Depreciation and amortization	2,272	2,263
Capital expenditures	487	265
Corporate and Other
Segment Reporting Information [Line Items]
Assets	106,268		79,996
Revenues	14,176	1,786
Depreciation and amortization	480	154
Capital expenditures	16,442	1,003
Eliminations
Segment Reporting Information [Line Items]
Assets	(386)		$ (249)
Revenues	$ (903)	$ (1,116)

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT - Estimated Aggregate Annual Amortization Expected to be Recognized (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Intangible assets
2018	$ 25,544
2019	33,171
2020	32,995
2021	29,303
2022	26,236
Unfavorable gas gathering contract
2018	1,349
2019	0
2020	0
2021	0
2022	$ 0

SEGMENT INFORMATION

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

SEGMENT INFORMATION

4. SEGMENT INFORMATION

As of March 31, 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.

	March 31, 2018			December 31, 2017
	(In thousands)
Assets:
Utica Shale	$	211,058		$	212,311
Ohio Gathering		682,227			690,485
Williston Basin		515,701			512,860
Piceance/DJ Basins		829,571			798,722
Barnett Shale		379,360			383,306
Marcellus Shale		215,587			217,362
Total reportable segment assets		2,833,504			2,815,046
Corporate and Other		106,268			79,996
Eliminations		(386	)		(249	)
Total assets	$	2,939,386		$	2,894,793

Revenues by reportable segment follow.

	Three months ended March 31,
	2018			2017
	(In thousands)
Revenues (1):
Utica Shale	$	10,041		$	8,796
Williston Basin		28,424			66,885
Piceance/DJ Basins		41,587			34,808
Barnett Shale		16,170			17,742
Marcellus Shale		7,825			6,904
Total reportable segments revenue		104,047			135,135
Corporate and Other		14,176			1,786
Eliminations		(903	)		(1,116	)
Total revenues	$	117,320		$	135,805

(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 March 31,
	2018			2017
Percentage of total revenues (1)(2):
Counterparty A - Piceance/DJ Basins		11	%	*
Counterparty B - Williston Basin	*				32	%

(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 March 31,
	2018		2017
	(In thousands)
Depreciation and amortization (1):
Utica Shale	$	1,853	$	1,647
Williston Basin		5,609		8,381
Piceance/DJ Basins		12,555		12,211
Barnett Shale (2)		3,757		3,762
Marcellus Shale		2,272		2,263
Total reportable segment depreciation and amortization		26,046		28,264
Corporate and Other		480		154
Total depreciation and amortization	$	26,526	$	28,418

(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.

	Three months ended March 31,
	2018		2017
	(In thousands)
Cash paid for capital expenditures (1):
Utica Shale	$	1,020	$	7,862
Williston Basin		5,888		429
Piceance/DJ Basins		16,904		5,864
Barnett Shale		37		(995	)
Marcellus Shale		487		265
Total reportable segment capital expenditures		24,336		13,425
Corporate and Other		16,442		1,003
Total cash paid for capital expenditures	$	40,778	$	14,428

(1) Excludes cash paid for capital expenditures by Ohio Gathering due to equity method accounting.

During the three months ended March 31, 2018, Corporate included cash paid of $0.3 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. We define segment adjusted EBITDA as total revenues less total costs and expenses; plus (i) other income excluding interest income, (ii) our proportional adjusted EBITDA for equity method investees (as defined below), (iii) depreciation and amortization, (iv) adjustments related to MVC shortfall payments, (v) adjustments related to capital reimbursement activity, (vi) unit-based and noncash compensation, (vii) change in the Deferred Purchase Price Obligation fair value, (viii) early extinguishment of debt expense, (ix) impairments and (x) other noncash expenses or losses, less other noncash income or gains. We define proportional adjusted EBITDA for our equity method investees as the product of (i) total revenues less total expenses, excluding impairments and other noncash income or expense items and (ii) amortization for deferred contract costs; multiplied by our ownership interest in Ohio Gathering during the respective period.

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 March 31,
	2018		2017
	(In thousands)
Reportable segment adjusted EBITDA
Utica Shale	$	8,715	$	7,912
Ohio Gathering		10,477		9,073
Williston Basin		15,970		17,809
Piceance/DJ Basins		29,235		28,974
Barnett Shale		9,859		12,088
Marcellus Shale		6,676		5,647
Total of reportable segments' measures of profit or loss	$	80,932	$	81,503

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

	Three months ended March 31,
	2018			2017
	(In thousands)
Reconciliation of (loss) income before income taxes and income (loss) from equity method investees to total of reportable segments' measures of profit or loss:
(Loss) income before income taxes and income (loss) from equity method investees	$	(5,402	)	$	525
Add:
Corporate and Other		10,623			10,093
Interest expense		15,122			16,716
Early extinguishment of debt		—			22,020
Deferred Purchase Price Obligation		21,658			20,883
Depreciation and amortization		26,526			28,418
Proportional adjusted EBITDA for equity method investees		10,477			9,073
Adjustments related to MVC shortfall payments		—			(28,640	)
Adjustments related to capital reimbursement activity		40			—
Unit-based and noncash compensation		1,962			2,128
(Gain) loss on asset sales, net		(74	)		3
Long-lived asset impairment		—			284
Total of reportable segments' measures of profit or loss	$	80,932		$	81,503

For the three months ended March 31, 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 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 months ended March 31, 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.

	Three months ended March 31, 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	)	$	(792	)	$	—	$	(38,485	)
Expected MVC shortfall adjustments		1,982			6,545			1,318		9,845
Total adjustments related to MVC shortfall payments	$	(35,711	)	$	5,753		$	1,318	$	(28,640	)

EARNINGS PER UNIT (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Schedule of earnings per limited partner unit

The following table details the components of EPU.

	Three months ended March 31,
	2018			2017
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net loss among limited partner interests:
Net loss attributable to limited partners	$	(5,988	)	$	(2,777	)
Less net income attributable to Series A Preferred Units		7,125			—
Net loss attributable to common limited partners	$	(13,113	)	$	(2,777	)

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic		73,134			72,149
Effect of nonvested phantom units		—			—
Weighted-average common units outstanding – diluted		73,134			72,149

Loss per limited partner unit:
Common unit – basic	$	(0.18	)	$	(0.04	)
Common unit – diluted	$	(0.18	)	$	(0.04	)

Nonvested anti-dilutive phantom units excluded from the calculation of diluted EPU		4			167

DEBT - Components of Long-Term Debt (Parenthetical) (Details) - SMP Holdings	Mar. 31, 2018	Dec. 31, 2017
Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Variable interest rate	3.90%	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%

EQUITY METHOD INVESTMENTS - Narrative (Details)	Mar. 31, 2018
Principal Owner \| OGC
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest	40.00%

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

3 Months Ended

Mar. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on property, plant and equipment follow.

	March 31, 2018		December 31, 2017
	(In thousands)
Gathering and processing systems and related equipment	$	2,014,522	$	1,973,722
Construction in progress		122,132		78,850
Land and line fill		11,735		11,735
Other		41,114		40,262
Total		2,189,503		2,104,569
Less accumulated depreciation		331,191		309,440
Property, plant and equipment, net	$	1,858,312	$	1,795,129

Schedule of depreciation expense and capitalized interest costs

Depreciation expense and capitalized interest follow.

	Three months ended March 31,
	2018		2017
	(In thousands)
Depreciation expense	$	18,557	$	18,491
Capitalized interest		1,222		468

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT

3 Months Ended

Mar. 31, 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.

	March 31, 2018
	Gross carrying amount		Accumulated amortization			Net
	(In thousands)
Favorable gas gathering contracts	$	24,195	$	(12,739	)	$	11,456
Contract intangibles		278,448		(124,356	)		154,092
Rights-of-way		160,931		(32,708	)		128,223
Total intangible assets	$	463,574	$	(169,803	)	$	293,771

Unfavorable gas gathering contract	$	10,962	$	(9,613	)	$	1,349

	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 March 31,
	2018			2017
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(389	)	$	(389	)
Amortization expense – unfavorable gas gathering contract		540			540

We recognized amortization expense in costs and expenses as follows:

	Three months ended March 31,
	2018		2017
	(In thousands)
Amortization expense – contract intangibles	$	6,535	$	8,551
Amortization expense – rights-of-way		1,585		1,527

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	$	25,544	$	1,349
2019		33,171		—
2020		32,995		—
2021		29,303		—
2022		26,236		—

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	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Property, plant and equipment, net	$ 1,858,312	$ 1,828,252	$ 1,795,129
Liabilities
Deferred revenue	10,159	10,088	4,000
Deferred revenue, noncurrent	36,587	35,528	12,707
Partners' Capital	1,032,442	1,088,644
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Property, plant and equipment, net	1,824,484		1,795,129
Liabilities
Deferred revenue	4,071		4,000
Deferred revenue, noncurrent	12,707		12,707
Partners' Capital	1,026,157		1,084,430
Adjustments Due to Topic 606
Liabilities
Deferred revenue			6,088
Deferred revenue, noncurrent			$ 22,821
Accounting Standard Update 2014-09 \| Adjustments Due to Topic 606
Assets
Property, plant and equipment, net	33,828	33,123
Liabilities
Deferred revenue	6,088	6,088
Deferred revenue, noncurrent	23,880	22,821
Partners' Capital	$ 6,285	$ 4,214

- Definition

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

+ References + Details

- Definition

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References + Details

FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Parenthetical) (Details) - Summit Holdings - USD ($)	Mar. 31, 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

CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Cash Flow Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$ 51,210	$ 62,449
Cash flows from investing activities:
Capital expenditures	(40,778)	(14,428)
Contributions to equity method investees	0	(4,936)
Other, net	(221)	(361)
Advances to affiliates	0	0
Net cash provided by (used in) investing activities	(40,999)	(19,725)
Cash flows from financing activities:
Distributions to unitholders	(45,053)	(44,452)
Borrowings under Revolving Credit Facility	50,000	72,000
Repayments under Revolving Credit Facility	(10,000)	(245,000)
Debt issuance costs	(4)	(6,825)
Payment of redemption and call premiums on senior notes	0	(17,913)
Proceeds from ATM Program common unit issuances, net of costs	0	367
Contribution from General Partner	0	113
Issuance of senior notes	0	500,000
Tender and redemption of senior notes	0	(300,000)
Other, net	(3,218)	(2,157)
Advances from affiliates	0	0
Net cash provided by (used in) financing activities	(8,275)	(43,867)
Net change in cash and cash equivalents	1,936	(1,143)
Cash and cash equivalents, beginning of period	1,430	7,428
Cash and cash equivalents, end of period	3,366	6,285
Consolidating adjustments
Cash flows from operating activities:
Net cash (used in) provided by operating activities	0	0
Cash flows from investing activities:
Capital expenditures	0	0
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	51,262	92,260
Net cash provided by (used in) investing activities	51,262	92,260
Cash flows from financing activities:
Distributions to unitholders	0	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	(51,262)	(92,260)
Net cash provided by (used in) financing activities	(51,262)	(92,260)
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 (used in) provided by operating activities	(2,721)	(2,021)
Cash flows from investing activities:
Capital expenditures	(297)	(1,003)
Contributions to equity method investees		0
Other, net	(221)	(361)
Advances to affiliates	0	(20,185)
Net cash provided by (used in) investing activities	(518)	(21,549)
Cash flows from financing activities:
Distributions to unitholders	(45,053)	(44,452)
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		367
Contribution from General Partner		113
Issuance of senior notes		0
Tender and redemption of senior notes		0
Other, net	(2,883)	(2,051)
Advances from affiliates	51,262	72,075
Net cash provided by (used in) financing activities	3,326	26,052
Net change in cash and cash equivalents	87	2,482
Cash and cash equivalents, beginning of period	126	698
Cash and cash equivalents, end of period	213	3,180
Co-Issuers \| Reportable Legal Entities
Cash flows from operating activities:
Net cash (used in) provided by operating activities	(10,985)	(27,574)
Cash flows from investing activities:
Capital expenditures	0	0
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	(28,718)	0
Net cash provided by (used in) investing activities	(28,718)	0
Cash flows from financing activities:
Distributions to unitholders	0	0
Borrowings under Revolving Credit Facility	50,000	72,000
Repayments under Revolving Credit Facility	(10,000)	(245,000)
Debt issuance costs	(4)	(6,825)
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	25,266
Net cash provided by (used in) financing activities	39,996	27,528
Net change in cash and cash equivalents	293	(46)
Cash and cash equivalents, beginning of period	75	51
Cash and cash equivalents, end of period	368	5
Guarantor Subsidiaries \| Reportable Legal Entities
Cash flows from operating activities:
Net cash (used in) provided by operating activities	47,495	75,271
Cash flows from investing activities:
Capital expenditures	(39,001)	(6,089)
Contributions to equity method investees		0
Other, net	0	0
Advances to affiliates	(6,995)	(72,075)
Net cash provided by (used in) investing activities	(45,996)	(78,164)
Cash flows from financing activities:
Distributions to unitholders	0	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	(306)	(91)
Advances from affiliates	0	0
Net cash provided by (used in) financing activities	(306)	(91)
Net change in cash and cash equivalents	1,193	(2,984)
Cash and cash equivalents, beginning of period	1,138	5,768
Cash and cash equivalents, end of period	2,331	2,784
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Cash flows from operating activities:
Net cash (used in) provided by operating activities	17,421	16,773
Cash flows from investing activities:
Capital expenditures	(1,480)	(7,336)
Contributions to equity method investees		(4,936)
Other, net	0	0
Advances to affiliates	(15,549)	0
Net cash provided by (used in) investing activities	(17,029)	(12,272)
Cash flows from financing activities:
Distributions to unitholders	0	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	(29)	(15)
Advances from affiliates	0	(5,081)
Net cash provided by (used in) financing activities	(29)	(5,096)
Net change in cash and cash equivalents	363	(595)
Cash and cash equivalents, beginning of period	91	911
Cash and cash equivalents, end of period	$ 454	$ 316

FINANCIAL INSTRUMENTS - Concentration Risk - Narrative (Details) - Customer	3 Months Ended	12 Months Ended
	Mar. 31, 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	47.00%	44.00%