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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2015	Jul. 31, 2015
Entity Information [Line Items]
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Jun. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Common units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		41,972,093
Subordinated Units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		24,409,850
General Partner Units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,354,700

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 26,973	$ 26,504
Accounts receivable	51,739	89,201
Other current assets	1,648	3,517
Total current assets	80,360	119,222
Property, plant and equipment, net	1,438,798	1,414,350
Intangible assets, net	458,625	477,734
Goodwill	265,062	265,062
Other noncurrent assets	15,908	17,353
Total assets	2,258,753	2,293,721
Current liabilities:
Trade accounts payable	13,806	24,855
Due to affiliate	4,936	2,711
Deferred revenue	677	2,377
Ad valorem taxes payable	6,482	9,118
Accrued interest	17,483	18,858
Other current liabilities	11,068	13,550
Total current liabilities	54,452	71,469
Long-term debt	879,000	808,000
Unfavorable gas gathering contract, net	5,239	5,577
Deferred revenue	62,784	55,239
Other noncurrent liabilities	1,343	1,715
Total liabilities	1,002,818	942,000
Commitments and contingencies
Common limited partner capital (41,972 units issued and outstanding at June 30, 2015 and 34,427 units issued and outstanding at December 31, 2014)	912,661	649,060
Subordinated limited partner capital (24,410 units issued and outstanding at June 30, 2015 and December 31, 2014)	312,269	293,153
General partner interests (1,355 units issued and outstanding at June 30, 2015 and 1,201 units issued and outstanding at December 31, 2014)	31,005	24,676
Summit Investments' equity in contributed subsidiaries	0	384,832
Total partners' capital	1,255,935	1,351,721
Total liabilities and partners' capital	$ 2,258,753	$ 2,293,721

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares shares in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common limited partner capital, units issued	41,972	34,427
Common limited partner capital, units outstanding	41,972	34,427
Subordinated limited partner capital, units issued	24,410	24,410
Subordinated limited partner capital, units outstanding	24,410	24,410
General partner interests, units issued	1,355	1,201
General partner interests, units outstanding	1,355	1,201

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues:
Gathering services and related fees	$ 61,370	$ 55,858	$ 122,137	$ 105,761
Natural gas, NGLs and condensate sales	11,967	26,703	24,580	53,007
Other revenues	3,937	3,423	7,718	6,597
Total revenues	77,274	85,984	154,435	165,365
Costs and expenses:
Cost of natural gas and NGLs	4,905	15,118	10,289	29,473
Operation and maintenance	21,616	22,797	42,673	44,628
General and administrative	9,374	9,659	19,032	18,712
Transaction costs	595	76	595	612
Depreciation and amortization	23,978	21,435	47,733	41,814
(Gain) loss on asset sales, net	(214)	6	(214)	6
Total costs and expenses	60,254	69,091	120,108	135,245
Other income	0	1	1	2
Interest expense	(12,083)	(10,803)	(24,201)	(17,947)
Income before income taxes	4,937	6,091	10,127	12,175
Income tax benefit (expense)	105	(469)	(72)	(628)
Net income	5,042	5,622	10,055	11,547
Less: net income attributable to Summit Investments	2,057	1,586	5,403	3,966
Net income attributable to SMLP	2,985	4,036	4,652	7,581
Less: net income attributable to general partner, including IDRs	1,891	801	3,459	1,232
Net income attributable to limited partners	$ 1,094	$ 3,235	$ 1,193	$ 6,349
Weighted-average limited partner units outstanding:
Cash distributions declared per common unit (in dollars per unit)	$ 0.565	$ 0.50	$ 1.125	$ 0.98
Cash distributions paid per common unit (in dollars per share)	$ 0.565	$ 0.500	$ 1.125	$ 0.83
Common units
Costs and expenses:
Net income attributable to limited partners	$ 1,847	$ 1,891	$ 1,490	$ 4,398
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.05	$ 0.05	$ 0.04	$ 0.14
Diluted (in dollars per share)	$ 0.05	$ 0.05	$ 0.04	$ 0.14
Weighted-average limited partner units outstanding:
Basic (shares)	38,278	34,422	36,369	32,179
Diluted (shares)	38,461	34,619	36,477	32,360
Subordinated Units
Costs and expenses:
Net income attributable to limited partners	$ (753)	$ 1,344	$ (297)	$ 1,951
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ (0.03)	$ 0.05	$ (0.01)	$ 0.08
Diluted (in dollars per share)	$ (0.03)	$ 0.05	$ (0.01)	$ 0.08
Weighted-average limited partner units outstanding:
Basic (shares)	24,410	24,410	24,410	24,410
Diluted (shares)	24,410	24,410	24,410	24,410

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) $ in Thousands	Total	Net Profit Interests	Summit Investments' equity in contributed subsidiaries	Summit Investments' equity in contributed subsidiaries Net Profit Interests	Limited partners, Common	Limited partners, Subordinated	General partner
Beginning balance at Dec. 31, 2013	$ 1,493,087		$ 523,944		$ 566,532	$ 379,287	$ 23,324
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	11,547		3,966		3,634	2,715	1,232
Distributions to unitholders	(56,749)				(31,169)	(23,922)	(1,658)
Unit-based compensation	2,424	$ 170	0	$ 170	2,424
Tax withholdings on vested SMLP LTIP awards	(656)				(656)
Issuance of common units, net of offering costs	197,989				197,989
Contribution from general partner	4,235						4,235
Purchase of contributed Subsidiaries	(305,000)		(305,000)
Excess of consideration paid over acquired carrying value of Red Rock Gathering			63,183		(36,228)	(25,691)	(1,264)
Cash advance from Summit Investments to contributed subsidiaries, net	22,326		22,326
Expenses paid by Summit Investments on behalf of contributed subsidiaries	7,423		7,423
Capitalized interest allocated from Summit Investments to contributed subsidiaries	331		331
Capital expenditures paid by Summit Investments to contributed subsidiaries	135		135
Repurchase of SMLP LTIP units	(228)				(228)
Ending balance at Jun. 30, 2014	1,377,034		316,478		702,298	332,389	25,869
Beginning balance at Dec. 31, 2014	1,351,721		384,832		649,060	293,153	24,676
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	10,055		5,403		715	478	3,459
Distributions to unitholders	(70,619)				(38,769)	(27,462)	(4,388)
Unit-based compensation	3,049	$ 85		$ 85	3,049
Tax withholdings on vested SMLP LTIP awards	(936)				(936)
Issuance of common units, net of offering costs	222,119				222,119
Contribution from general partner	4,737						4,737
Purchase of contributed Subsidiaries	(290,000)		(290,000)
Excess of acquired carrying value over consideration paid for Polar and Divide			(126,044)		77,423	46,100	2,521
Cash advance from Summit Investments to contributed subsidiaries, net	21,719		21,719
Expenses paid by Summit Investments on behalf of contributed subsidiaries	3,084		3,084
Capitalized interest allocated from Summit Investments to contributed subsidiaries	921		921
Capital expenditures paid by Summit Investments to contributed subsidiaries	0
Ending balance at Jun. 30, 2015	$ 1,255,935		$ 0		$ 912,661	$ 312,269	$ 31,005

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 10,055	$ 11,547
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	48,196	42,265
Amortization of deferred loan costs	1,591	1,220
Unit-based compensation	3,134	2,594
(Gain) loss on asset sales, net	(214)	6
Changes in operating assets and liabilities:
Accounts receivable	37,463	14,067
Trade accounts payable	(3,849)	2,481
Due to affiliate	5,162	925
Change in deferred revenue	5,845	8,464
Ad valorem taxes payable	(2,635)	(1,259)
Accrued interest	(1,375)	(894)
Other, net	(1,044)	623
Net cash provided by operating activities	102,329	82,039
Cash flows from investing activities:
Capital expenditures	(60,175)	(88,033)
Proceeds from asset sales	238	24
Acquisitions of gathering systems from affiliate	(292,941)	(305,000)
Net cash used in investing activities	(352,878)	(393,009)
Cash flows from financing activities:
Distributions to unitholders	(70,619)	(56,749)
Borrowings under revolving credit facility	122,000	160,000
Repayments under revolving credit facility	(51,000)	(20,000)
Deferred loan costs	(86)	(300)
Tax withholdings on vested SMLP LTIP awards	(936)	(656)
Proceeds from issuance of common units, net	222,119	197,989
Contribution from general partner	4,737	4,235
Cash advance from Summit Investments to contributed subsidiaries, net	21,719	22,326
Expenses paid by Summit Investments on behalf of contributed subsidiaries	3,084	7,423
Repurchase of equity-based compensation awards	0	(228)
Net cash provided by financing activities	251,018	314,040
Net change in cash and cash equivalents	469	3,070
Cash and cash equivalents, beginning of period	26,504	20,357
Cash and cash equivalents, end of period	26,973	23,427
Supplemental cash flow disclosures:
Cash interest paid	24,731	17,153
Less: capitalized interest	1,651	4,019
Interest paid (net of capitalized interest)	23,080	13,134
Noncash investing and financing activities:
Capital expenditures in trade accounts payable (period-end accruals)	10,877	33,115
Excess of acquired carrying value over consideration paid for Polar and Divide	126,044	0
Capitalized interest allocated from Summit Investments to contributed subsidiaries	921	331
Capital expenditures paid by Summit Investments to contributed subsidiaries	0	135
Excess of consideration paid over acquired carrying value of Red Rock Gathering	$ 0	$ (63,183)

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

6 Months Ended

Jun. 30, 2015

Organization, Consolidation and Presentation of Financial Statements [Abstract]

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION

Organization. Summit Midstream Partners, LP ("SMLP" or the "Partnership"), a Delaware limited partnership, 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 North America.

SMLP and its subsidiaries are managed and operated by the board of directors and executive officers of Summit Midstream GP, LLC (the "general partner"). Summit Investments, as the ultimate owner of our general partner, controls us and has the right to appoint the entire board of directors of our general partner, including our independent directors. Our operations are conducted through, and our operating assets are owned by, various wholly-owned operating subsidiaries. Neither SMLP nor its subsidiaries have any employees. All of the personnel that conduct our business are employed by the general partner and its subsidiaries, but these individuals are sometimes referred to as our employees.

As of June 30, 2015, Summit Midstream Partners Holdings, LLC ("SMP Holdings"), a wholly owned subsidiary of Summit Investments, held 5,293,571 SMLP common units, all of our subordinated units, all of our general partner units representing a 2% general partner interest in SMLP and all of our incentive distribution rights ("IDRs").

On May 18, 2015, the Partnership acquired certain crude oil and produced water gathering systems and under-development transmission pipelines held by Polar Midstream, LLC ("Polar Midstream") and Epping Transmission Company, LLC ("Epping") located in the Williston Basin (collectively the "Polar and Divide system") from SMP Holdings (the "Polar and Divide Drop Down"). Polar Midstream and Epping are Delaware limited liability companies formed in April 2014.

Polar Midstream's assets were carved out of Meadowlark Midstream Company, LLC ("Meadowlark Midstream"), a subsidiary of Summit Investments, immediately prior to the Polar and Divide Drop Down. Concurrent with the closing of the Polar and Divide Drop Down, Epping became a wholly owned subsidiary of Polar Midstream and SMLP contributed Polar Midstream (including Epping) to Bison Midstream, LLC ("Bison Midstream"). Because the Polar and Divide system was acquired from subsidiaries of Summit Investments, it was deemed a transaction among entities under common control. Common control began in (i) February 2013 for Polar Midstream and (ii) April 2014 for Epping.

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. Our gathering systems and the unconventional resource basins in which they operate are as follows:


•	the Mountaineer Midstream system ("Mountaineer Midstream"), a natural gas gathering system located in the Appalachian Basin, which includes the Marcellus Shale formation in northern West Virginia;


•	Bison Midstream, an associated natural gas gathering system located in the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota;


•	the Polar and Divide system ("Polar and Divide"), a crude oil and produced water gathering system and transmission pipelines (under development) located in the Williston Basin;


•	DFW Midstream Services LLC ("DFW Midstream"), a natural gas gathering system located in the Fort Worth Basin, which includes the Barnett Shale formation in north-central Texas; and


•	Grand River Gathering, LLC ("Grand River Gathering"), 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.

Our operating subsidiaries, which are wholly owned by our wholly owned subsidiary, Summit Midstream Holdings, LLC ("Summit Holdings"), are: DFW Midstream (which includes Mountaineer Midstream); Bison Midstream (and its wholly owned subsidiaries Polar Midstream and Epping); and Grand River Gathering (and its wholly owned subsidiary Red Rock Gathering Company, LLC ("Red Rock Gathering")). All of our operating subsidiaries are focused on the development, construction and operation of natural gas gathering and processing systems and crude oil and produced water gathering systems.

Presentation and Consolidation. We prepare our unaudited condensed consolidated financial statements in accordance with accounting principles generally accepted in the United States of America ("GAAP"). These principles are established by the Financial Accounting Standards Board (the "FASB"). The unaudited condensed consolidated financial statements include the assets, liabilities, and results of operations of SMLP and its subsidiaries. All intercompany transactions among the consolidated entities have been eliminated in consolidation.

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 Securities and Exchange Commission (the "SEC"). Certain information and note disclosures normally included in 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 accruals, which are necessary to fairly present the unaudited condensed consolidated balance sheet as of June 30, 2015, the unaudited condensed consolidated statements of operations for the three- and six-month periods ended June 30, 2015 and 2014, and the unaudited condensed consolidated statements of partners' capital and cash flows for the six-month periods ended June 30, 2015 and 2014. 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, 2014 as filed with the SEC on March 2, 2015 (the "2014 Annual Report"). The results of operations for an interim period are not necessarily indicative of results expected for a full year.

SMLP recognized its acquisitions of (i) Polar Midstream and Epping and (ii) Red Rock Gathering (the "Red Rock Drop Down") at Summit Investments' historical cost of construction or fair value of assets and liabilities at acquisition because the acquisitions were executed by entities under common control. The excess of Summit Investments' net investment in Polar Midstream and Epping was recognized as an addition to partners' capital. The excess of the purchase price paid by SMLP over Summit Investments' net investment in Red Rock Gathering was recognized as a reduction to partners' capital. Due to the common control aspect, the Polar and Divide Drop Down and the Red Rock Drop Down were accounted for by the Partnership on an “as-if pooled” basis for the periods during which common control existed. For the purposes of these unaudited condensed consolidated financial statements, SMLP's results of operations reflect the results of operations of Polar Midstream, Epping and Red Rock Gathering for all periods presented.

The financial position, results of operations and cash flows of Polar Midstream included herein have been derived from the accounting records of Meadowlark Midstream on a carve-out basis. The majority of the assets and liabilities allocated to Polar Midstream have been specifically identified based on Meadowlark Midstream’s existing divisional organization. Goodwill was allocated to Polar Midstream based on initial purchase accounting estimates. Revenues and depreciation and amortization have been specifically identified based on Polar Midstream's relationship to Meadowlark Midstream’s existing divisional structure. Operation and maintenance and general and administrative expenses have been allocated to Polar Midstream based on volume throughput. These allocations and estimates were based on methodologies that management believes are reasonable. The results reflected herein, however, may not reflect what Polar Midstream’s financial position, results of operations or cash flows would have been if Polar Midstream been a stand-alone company.

Reclassifications. Certain reclassifications have been made to prior-year amounts to conform to current-year presentation. In the second quarter of 2015, we evaluated our classification of revenues and concluded that creating an “other revenues” category would provide reporting that was more reflective of our results of operations and how we manage our business. As such, certain revenue transactions that represented the “and other” portions of (i) gathering services and (ii) natural gas, NGLs and condensate sales have been reclassified to other revenues. Other revenues also includes the amortization expense associated with our favorable and unfavorable gas gathering contracts. The amounts reclassified to other revenues for each period presented can be determined based on the total of the other revenues line item and the amount of amortization of favorable and unfavorable gas gathering contracts disclosed in Note 5. Also in the second quarter or 2015, we evaluated our historical classification of electricity expense for Bison Midstream. In connection with the reclassification of certain revenues noted above and to be consistent with the classification of pass-through electricity expense for our other operating segments, we reclassified pass-through electricity expenses for Bison Midstream ($1.4 million and $1.3 million for the three months ended June 30, 2015 and 2014, respectively, and $2.7 million and $2.2 million for the six months ended June 30, 2015 and 2014, respectively) from costs of natural gas and NGLs to operation and maintenance. These reclassifications had no impact on total revenues, total costs and expenses, net income, total partners' capital or segment adjusted EBITDA.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Jun. 30, 2015
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Comprehensive Income. Comprehensive income is the same as net income for all periods presented. Environmental Matters. We are subject to various federal, state and local laws and regulations relating to the protection of the environment. Liabilities for loss contingencies, including environmental remediation costs, arising from claims, assessments, litigation, fines, and penalties and other sources are charged to expense when it is probable that a liability has been incurred and the amount of the assessment and/or remediation can be reasonably estimated. We accrue for losses associated with environmental remediation obligations when such losses are probable and reasonably estimable. Such accruals are adjusted as further information develops or circumstances change. Recoveries of environmental remediation costs from other parties or insurers are recorded as assets when their receipt is deemed probable. Other Significant Accounting Policies. For information on our other significant accounting policies, see Note 2 of the consolidated financial statements included in the 2014 Annual Report. 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. There are currently no recent pronouncements that have been issued that we believe may materially affect our financial statements, except as noted below. In May 2014, the FASB released a joint revenue recognition standard, Accounting Standards Update ("ASU") No. 2014-09 Revenue From Contracts With Customers (Topic 606) ("ASU 2014-09"). Under ASU 2014-09, revenue will be recognized under a five-step model: (i) identify the contract with the customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to performance obligations; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. In its original form, ASU 2014-09 was effective for fiscal years, and interim periods within those years, beginning after December 15, 2016; early adoption was not permitted. In July 2015, the FASB reaffirmed the guidance in its April 2015 proposed ASU that defers for one year the effective date of the ASU 2014-09 for both public and nonpublic entities reporting under U.S. GAAP and allows early adoption as of the original effective date. We are currently in the process of evaluating the impact of this update. In February 2015, the FASB issued ASU No. 2015-02—Consolidation (Topic 810): Amendments to the Consolidation Analysis ("ASU 2015-02"). The standard changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities. This new standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015, and interim and annual periods thereafter. Early adoption is permitted. We are currently in the process of evaluating the impact of this update. In April 2015, the FASB issued ASU No. 2015-03—Interest—Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs ("ASU 2015-03"). Under ASU 2015-03, entities that have historically presented debt issuance costs as an asset, related to a recognized debt liability, will be required to present those costs as a direct deduction from the carrying amount of that debt liability. This presentation will result in debt issuance cost being presented the same way debt discounts have historically been handled. This new standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015, and interim and annual periods thereafter. Early adoption is permitted. We are currently in the process of evaluating the impact of this update.

SEGMENT INFORMATION

6 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

Segment Information

SEGMENT INFORMATION

As of June 30, 2015, our reportable segments are:


•	the Marcellus Shale, which is served by Mountaineer Midstream;


•	the Williston Basin – Gas, which is served by Bison Midstream;


•	the Williston Basin – Liquids, which is served by Polar and Divide;


•	the Barnett Shale, which is served by DFW Midstream; and


•	the Piceance Basin, which is served by Grand River Gathering.

Each of our reportable segments provides midstream services in a specific geographic area. Within specific geographic areas, we may further differentiate reportable segments by type of gathering service provided. 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.

In the first quarter of 2015, we combined our Red Rock Gathering operating segment with the Grand River Gathering operating segment to become one operating segment serving the Piceance Basin. Prior to 2015, we aggregated the Red Rock Gathering and Grand River Gathering operating segments into the Piceance Basin reportable segment.

In the second quarter of 2015, in connection with the Polar and Divide Drop Down, we identified two reportable segments in the Williston Basin. We had previously only provided natural gas gathering services in the Williston Basin. With the acquisition of Polar Midstream and Epping in May 2015, we now also provide crude oil and produced water gathering services in the Williston Basin. As such, we evaluated the quantitative and qualitative factors for operating segment aggregation in the Williston Basin and concluded that the characteristics for crude oil and produced water gathering services were not sufficiently similar to those of our natural gas gathering services. As a result, we now report the results of Bison Midstream in the Williston Basin – Gas reportable segment and those of Polar Midstream and Epping in the Williston Basin – Liquids reportable segment.

Corporate represents those revenues and expenses that are not specifically attributable to a reportable segment, not individually reportable, or that have not been allocated to our reportable segments. Beginning in the first quarter of 2015, we discontinued allocating certain general and administrative expenses, primarily salaries, benefits, incentive compensation and rent expense, to our operating segments.

Assets by reportable segment follow.



	June 30,		December 31,
	2015		2014
	(In thousands)
Assets:
Marcellus Shale	$	239,384	$	243,884
Williston Basin – Gas	294,725		311,041
Williston Basin – Liquids	431,951		398,847
Barnett Shale	424,706		428,935
Piceance Basin	833,385		872,437
Total reportable segment assets	2,224,151		2,255,144
Corporate	34,602		38,577
Total assets	$	2,258,753	$	2,293,721

Revenues by reportable segment follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Revenues:
Marcellus Shale	$	7,783	$	5,665	$	15,622	$	11,021
Williston Basin – Gas	7,454		14,819		16,364		31,582
Williston Basin – Liquids	9,906		5,188		18,487		8,367
Barnett Shale	23,823		24,241		47,720		47,277
Piceance Basin	28,308		36,071		56,242		67,118
Total reportable segment revenues and total revenues	$	77,274	$	85,984	$	154,435	$	165,365

Depreciation and amortization by reportable segment follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Depreciation and amortization:
Marcellus Shale	$	2,169	$	1,861	$	4,338	$	3,661
Williston Basin – Gas	4,778		4,488		9,476		8,737
Williston Basin – Liquids	1,735		955		3,347		1,692
Barnett Shale	3,902		3,739		7,808		7,376
Piceance Basin	11,210		10,250		22,414		20,063
Total reportable segments	23,794		21,293		47,383		41,529
Corporate	184		142		350		285
Total depreciation and amortization	$	23,978	$	21,435	$	47,733	$	41,814

Capital expenditures by reportable segment follow.



	Six months ended June 30,
	2015		2014
	(In thousands)
Capital expenditures:
Marcellus Shale	$	637	$	10,969
Williston Basin – Gas	8,699		21,884
Williston Basin – Liquids	38,790		24,697
Barnett Shale	1,922		9,856
Piceance Basin	9,734		20,564
Total reportable segments	59,782		87,970
Corporate	393		63
Total capital expenditures	$	60,175	$	88,033

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) depreciation and amortization, (iii) adjustments related to minimum volume commitment ("MVC") shortfall payments, (iv) impairments and (v) other noncash expenses or losses, less other noncash income or gains. Segment adjusted EBITDA excludes the effect of allocated corporate expenses, such as certain general and administrative expenses (including compensation-related expenses and professional services fees) interest expense and income tax expense.

Adjustments related to MVC shortfall payments 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. We include a proportional amount of these historical or expected minimum volume commitment shortfall payments in each quarter prior to the quarter in which we actually recognize the shortfall payment. These adjustments have not been billed to our customers and are not recognized in our consolidated financial statements.

A reconciliation of income before income taxes to total reportable segment adjusted EBITDA follows.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Reconciliation of Income Before Income Taxes to Segment Adjusted EBITDA:
Income before income taxes	$	4,937	$	6,091	$	10,127	$	12,175
Add:
Interest expense	12,083		10,803		24,201		17,947
Depreciation and amortization	24,190		21,660		48,196		42,265
Adjustments related to MVC shortfall payments	10,928		10,577		23,268		22,590
Unit-based compensation	1,737		1,446		3,134		2,594
Loss on asset sales	—		6		—		6
Allocated corporate expenses	6,142		2,428		12,000		4,983
Less:
Interest income	—		1		1		2
Gain on asset sales	214		—		214		—
Total reportable segment adjusted EBITDA	$	59,803	$	53,010	$	120,711	$	102,558

Segment adjusted EBITDA by reportable segment follows.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Reportable segment adjusted EBITDA:
Marcellus Shale	$	6,162	$	3,837	$	12,696	$	7,721
Williston Basin – Gas	4,740		4,809		10,075		9,485
Williston Basin – Liquids	6,497		2,626		11,540		3,000
Barnett Shale	15,540		14,958		32,301		29,991
Piceance Basin	26,864		26,780		54,099		52,361
Total reportable segment adjusted EBITDA	$	59,803	$	53,010	$	120,711	$	102,558

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8971-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8595-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8380-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8984-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e9031-108599

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e9054-108599

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8538-108599

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 29
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8864-108599

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8924-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=51669610&loc=d3e8906-108599

+ Details

PROPERTY, PLANT, AND EQUIPMENT, NET

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT, NET

Details on property, plant, and equipment, net follow.



	Useful lives (In years)	June 30,		December 31,
	Useful lives (In years)	2015		2014
		(Dollars in thousands)
Gathering and processing systems and related equipment	30	$	1,510,375	$	1,462,706
Construction in progress	n/a	48,226		44,447
Other	4-15	29,360		28,871
Total		1,587,961		1,536,024
Less accumulated depreciation		149,163		121,674
Property, plant, and equipment, net		$	1,438,798	$	1,414,350

Construction in progress is depreciated consistent with its applicable asset class once it is placed in service. Depreciation expense and capitalized interest were as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Depreciation expense	$	13,851	$	12,000	$	27,489	$	23,197
Capitalized interest	1,003		2,388		1,651		4,019

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT

6 Months Ended

Jun. 30, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

AMORTIZING INTANGIBLE ASSETS AND LIABILITIES AND UNFAVORABLE GAS GATHERING CONTRACT

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT

Details regarding our intangible assets and the unfavorable gas gathering contract, all of which are subject to amortization, follow.



	June 30, 2015
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(8,857	)	$	15,338
Contract intangibles	12.5	426,464		(93,383		)	333,081
Rights-of-way	24.3	125,517		(15,311		)	110,206
Total intangible assets		$	576,176	$	(117,551	)	$	458,625

Unfavorable gas gathering contract	10.0	$	10,962	$	(5,723	)	$	5,239



	December 31, 2014
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(8,056	)	$	16,139
Contract intangibles	12.5	426,464		(75,713		)	350,751
Rights-of-way	24.7	123,581		(12,737		)	110,844
Total intangible assets		$	574,240	$	(96,506	)	$	477,734

Unfavorable gas gathering contract	10.0	$	10,962	$	(5,385	)	$	5,577

We recognized amortization expense in other revenues as follows:



	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(375	)	$	(436	)	$	(801	)	$	(870	)
Amortization expense – unfavorable gas gathering contract	163			211			338			419

We recognized amortization expense in costs and expenses as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Amortization expense – contract intangibles	$	8,835	$	8,198	$	17,670	$	16,160
Amortization expense – rights-of-way	1,293		1,239		2,574		2,457

The estimated aggregate annual amortization expected to be recognized for the remainder of 2015 and each of the four succeeding fiscal years follows.



	Intangible assets		Unfavorable gas gathering contract
	(In thousands)
2015	$	21,135	$	368
2016	42,288		924
2017	41,139		1,047
2018	40,593		1,035
2019	40,838		1,045

GOODWILL

6 Months Ended

Jun. 30, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL

We evaluate goodwill for impairment annually on September 30 and 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 amount. There have been no impairments of goodwill during the six months ended June 30, 2015.

Annual Impairment Evaluation. We performed our annual goodwill impairment testing as of September 30, 2014 using a combination of the income and market approaches. Details on the results of the annual goodwill impairment testing for all reporting units except those acquired in the Polar and Divide Drop Down are included in our 2014 Annual Report. The assets acquired in the Polar and Divide Drop Down were carved out of Meadowlark Midstream. As such, we elected to apply the historical cost approach to determine the amount of goodwill to assign to Polar Midstream. Our procedures indicated that the remaining goodwill balance at Meadowlark Midstream was entirely attributable to Polar Midstream. We then performed the quantitative analysis for the Polar Midstream reporting unit and determined that the fair value of the Polar Midstream reporting unit substantially exceeded its carrying value, including goodwill as of September 30, 2014. Because the fair value of the Polar Midstream reporting unit exceeded its carrying value, including goodwill, there was no associated impairment of goodwill in connection with our 2014 annual goodwill impairment test and therefore no impairment of the $203.4 million of goodwill that was allocated to the Polar Midstream reporting unit. Because Epping was an organic growth project, it has no goodwill.

Bison Midstream Fourth Quarter 2014 Goodwill Impairment. In the first quarter of 2015, we finalized our calculations of the fair values of the identified assets and liabilities in step two of the December 31, 2014 goodwill impairment testing for the Bison Midstream reporting unit. This process confirmed the preliminary goodwill impairment of $54.2 million that was recognized as of December 31, 2014.

Polar Midstream Fourth Quarter 2014 Goodwill Impairment Evaluation. During the latter part of the fourth quarter of 2014, the declines in prices for natural gas, NGLs and crude oil accelerated, negatively impacting producers in each of our areas of operation. As a result, we considered whether the goodwill associated with our Polar Midstream reporting unit could have been impaired. Our assessment related to the Polar Midstream reporting unit did result in an indication that the associated goodwill could have been impaired.

We noted that the reporting unit had been impacted by the recent price declines thereby increasing the likelihood that the associated goodwill could have been impaired. As such, we concluded that a triggering event occurred during the fourth quarter of 2014 requiring that we test Polar Midstream's goodwill.

In connection therewith, we reperformed our step one analysis as of December 31, 2014. To estimate the fair value of the reporting unit, we utilized two valuation methodologies: the market approach and the income approach. Both of these approaches incorporate significant estimates and assumptions to calculate enterprise fair value for a reporting unit. The most significant estimates and assumptions inherent within these two valuation methodologies are:


•	determination of the weighted-average cost of capital;


•	the selection of guideline public companies;


•	market multiples;


•	weighting of the income and market approaches;


•	growth rates;


•	commodity prices; and


•	the expected levels of throughput volume gathered.

Changes in the above and other assumptions could materially affect the estimated amount of fair value for any of our reporting units.

The results of our step one goodwill impairment testing indicated that the fair value of the Polar Midstream reporting unit substantially exceeded its carrying value, including goodwill as of December 31, 2014. As a result, there was no associated impairment of goodwill in connection with the fourth quarter 2014 triggering event and no impairment of goodwill acquired in connection with the Polar and Divide Drop Down.

Our impairment determinations, in the context of (i) our annual impairment evaluation and (ii) our fourth quarter 2014 evaluations, involved significant assumptions and judgments, as discussed above. 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.

DEFERRED REVENUE

6 Months Ended

Jun. 30, 2015

Deferred Revenue Disclosure [Abstract]

Deferred Revenue

DEFERRED REVENUE

A rollforward of current deferred revenue follows.



	Williston Basin - Gas		Barnett Shale		Piceance Basin		Total current
	(In thousands)
Current deferred revenue, January 1, 2015	$	—	$	2,377	$	—	$	2,377
Additions	—		999		—		999
Less: revenue recognized	—		2,699		—		2,699
Current deferred revenue, June 30, 2015	$	—	$	677	$	—	$	677

A rollforward of noncurrent deferred revenue follows.



	Williston Basin - Gas		Barnett Shale		Piceance Basin		Total noncurrent
	(In thousands)
Noncurrent deferred revenue, January 1, 2015	$	17,132	$	—	$	38,107	$	55,239
Additions	—		—		7,572		7,572
Less: revenue recognized	27		—		—		27
Noncurrent deferred revenue, June 30, 2015	$	17,105	$	—	$	45,679	$	62,784

As of June 30, 2015, accounts receivable included $3.2 million of shortfall billings related to MVC arrangements that can be utilized to offset gathering fees in subsequent periods. Noncurrent deferred revenue at June 30, 2015 represents amounts that provide certain customers the ability to offset their gathering fees over a period up to six years to the extent that the customer's throughput volumes exceeds its MVC.

LONG-TERM DEBT

6 Months Ended

Jun. 30, 2015

Debt Disclosure [Abstract]

LONG-TERM DEBT

Long-term debt consisted of the following:



	June 30,		December 31,
	2015		2014
	(In thousands)
Variable rate senior secured revolving credit facility (2.44% at June 30, 2015 and 2.67% at December 31, 2014) due November 2018	$	279,000	$	208,000
5.50% Senior unsecured notes due August 2022	300,000		300,000
7.50% Senior unsecured notes due July 2021	300,000		300,000
Total long-term debt	$	879,000	$	808,000

Revolving Credit Facility. We have a senior secured revolving credit facility which allows for revolving loans, letters of credit and swingline loans (the "revolving credit facility"). The revolving credit facility has a $700.0 million borrowing capacity, matures in November 2018, and includes a $200.0 million accordion feature. It is secured by the membership interests of Summit Holdings and those of its subsidiaries. Substantially all of the assets of Summit Holdings and its subsidiaries are pledged as collateral under the revolving credit facility. The revolving credit facility, and Summit Holdings' obligations, are guaranteed by SMLP and each of its subsidiaries.

As of June 30, 2015, we were in compliance with the revolving credit facility's covenants. There were no defaults or events of default during the six months ended June 30, 2015.

Senior Notes. In July 2014, Summit Holdings and its 100% owned finance subsidiary, Summit Midstream Finance Corp. ("Finance Corp.," together with Summit Holdings, the "Co-Issuers"), co-issued $300.0 million of 5.50% senior unsecured notes maturing August 15, 2022 (the "5.5% senior notes"). In June 2013, the Co-Issuers co-issued $300.0 million of 7.50% senior unsecured notes maturing July 1, 2021 (the "7.5% senior notes").

SMLP and all of its subsidiaries other than the Co-Issuers (the "Guarantors") have fully and unconditionally and jointly and severally guaranteed the 5.5% senior notes and the 7.5% senior notes. SMLP has no independent assets or operations. Summit Holdings has no assets or operations other than its ownership of its wholly owned subsidiaries and activities associated with its borrowings under the revolving credit facility, the 5.5% senior notes and the 7.5% senior notes. Finance Corp. has no independent assets or operations and was formed for the sole purpose of being a co-issuer of certain of Summit Holdings' indebtedness, including the 5.5% senior notes and the 7.5% senior notes. There are no significant restrictions on the ability of SMLP or Summit Holdings to obtain funds from their subsidiaries by dividend or loan.

As of June 30, 2015, we were in compliance with the covenants of the 5.5% senior notes and the 7.5% senior notes. There were no defaults or events of default during the six months ended June 30, 2015.

Fair Value of Debt Instruments. A summary of the estimated fair value of our debt financial instruments follows.



	June 30, 2015				December 31, 2014
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Revolving credit facility	$	279,000	$	279,000	$	208,000	$	208,000
5.5% Senior notes	300,000		286,500		300,000		281,750
7.5% Senior notes	300,000		313,250		300,000		306,750

The revolving credit facility’s carrying value on the balance sheet 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 June 30, 2015 and December 31, 2014. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the senior notes.

PARTNERS' CAPITAL

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

PARTNERS' CAPITAL

A rollforward of the number of common limited partner, subordinated limited partner and general partner units follows.



	Common	Subordinated	General partner	Total
Units, January 1, 2015	34,426,513	24,409,850	1,200,651	60,037,014
Units issued in connection with the May 2015 Equity Offering (1)	7,475,000	—	152,551	7,627,551
Units issued under SMLP LTIP (2)	70,580	—	1,498	72,078
Units, June 30, 2015	41,972,093	24,409,850	1,354,700	67,736,643

__________

(1) Including issuance to general partner in connection with contributions made to maintain 2% general partner interest.

(2) Net of 19,702 units withheld to meet minimum statutory tax withholding requirements

On May 13, 2015, we completed an underwritten public offering of 6,500,000 common units at a price of $30.75 per unit pursuant to an effective shelf registration statement on Form S-3 previously filed with the SEC (the "May 2015 Equity Offering"). On May 22, 2015, the underwriters exercised in full their option to purchase an additional 975,000 common units from us at a price of $30.75 per unit. Concurrent with both transactions, our general partner made a capital contribution to us to maintain its 2% general partner interest.

In June 2015, we concurrently executed an 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 "June 2015 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. There were no transactions under the June 2015 ATM Program during the period from inception through June 30, 2015.

Polar and Divide Drop Down. On May 18, 2015, we acquired 100% of the membership interests in Polar Midstream and Epping from a subsidiary of Summit Investments. We paid total cash consideration of $290.0 million in exchange for Summit Investments' $416.0 million net investment in Polar Midstream and Epping (see Note 15 for additional information). We recognized a capital contribution from Summit Investments for the difference between cash consideration paid and Summit Investments' net investment in Polar Midstream and Epping. The calculation of the capital contribution and its allocation to partners' capital follow (dollars in thousands).



Summit Investments' net investment in Polar Midstream and Epping			$	416,044
Total cash consideration paid to a subsidiary of Summit Investments			290,000
Excess of acquired carrying value over consideration paid			$	126,044

Allocation of capital contribution:
General partner interest	$	2,521
Common limited partner interest	77,423
Subordinated limited partner interest	46,100
Partners' capital contribution – excess of acquired carrying value over consideration paid			$	126,044

Red Rock Drop Down. On March 18, 2014, we acquired 100% of the membership interests in Red Rock Gathering from a subsidiary of Summit Investments. We paid total cash consideration of $307.9 million (including working capital adjustments accrued in December 2014 and cash settled in February 2015) in exchange for Summit Investments' net investment in Red Rock Gathering. As a result of the excess of the purchase price over acquired carrying value of Red Rock Gathering, SMLP recognized a capital distribution to Summit Investments. The calculation of the capital distribution and its allocation to partners' capital follow (dollars in thousands).



Summit Investments' net investment in Red Rock Gathering				$	241,817
Total cash consideration paid to a subsidiary of Summit Investments				307,941
Excess of consideration paid over acquired carrying value				$	(66,124	)

Allocation of capital distribution:
General partner interest	$	(1,323	)
Common limited partner interest	(37,910		)
Subordinated limited partner interest	(26,891		)
Partners' capital distribution – excess of consideration paid over acquired carrying value				$	(66,124	)

Details of cash distributions declared in 2015 follow.



Attributable to the quarter ended	Payment date	Per-unit distribution		Cash paid to common unitholders		Cash paid to subordinated unitholders		Cash paid to general partner		Cash paid for IDRs		Total distribution
		(In thousands, except per-unit amounts)
December 31, 2014	February 13, 2015	$	0.5600	$	19,279	$	13,670	$	702	$	1,442	$	35,093
March 31, 2015	May 15, 2015	$	0.5650	$	19,490	$	13,792	$	710	$	1,534	$	35,526

On July 22, 2015, the board of directors of our general partner declared a distribution of $0.57 per unit attributable to the quarter ended June 30, 2015. The distribution will be paid on August 14, 2015 to unitholders of record at the close of business on August 7, 2015.

Summit Investments' Equity in Contributed Subsidiaries. Summit Investments' equity in contributed subsidiaries represents its position in the net assets of Polar and Divide and Red Rock Gathering that have been acquired by SMLP. The balance also reflects net income attributable to Summit Investments for Polar and Divide and Red Rock Gathering for the periods beginning on their respective acquisition dates by Summit Investments and ending on the dates they were acquired by the Partnership. For the three and six months ended June 30, 2015 and 2014, net income was attributed to Summit Investments for (i) Polar and Divide for the period from January 1, 2015 to May 18, 2015 as well as the three and six months ended June 30, 2014 and (ii) Red Rock Gathering for the period from January 1, 2014 to March 18, 2014. Although included in partners' capital, these net income amounts have been excluded from the calculation of earnings per unit ("EPU").

EARNINGS PER UNIT

6 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

EARNINGS PER UNIT

The following table details the components of earnings per limited partner unit.



	Three months ended June 30,					Six months ended June 30,
	2015			2014		2015			2014
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net income among limited partner interests:
Net income attributable to common units	$	1,847		$	1,891	$	1,490		$	4,398
Net (loss) income attributable to subordinated units	(753		)	1,344		(297		)	1,951
Net income attributable to limited partners	$	1,094		$	3,235	$	1,193		$	6,349

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic	38,278			34,422		36,369			32,179
Effect of nonvested phantom units	183			197		108			181
Weighted-average common units outstanding – diluted	38,461			34,619		36,477			32,360

Weighted-average subordinated units outstanding – basic and diluted	24,410			24,410		24,410			24,410

Earnings (loss) per limited partner unit:
Common unit – basic	$	0.05		$	0.05	$	0.04		$	0.14
Common unit – diluted	$	0.05		$	0.05	$	0.04		$	0.14
Subordinated unit – basic and diluted	$	(0.03	)	$	0.05	$	(0.01	)	$	0.08

We excluded 94,892 units in our calculation of the effect of nonvested phantom units for the six months ended June 30, 2015 because they were anti-dilutive. There were no anti-dilutive units during the three months ended June 30, 2015 or during the three and six months ended June 30, 2014.

UNIT-BASED COMPENSATION	6 Months Ended
UNIT-BASED COMPENSATION	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
UNIT-BASED COMPENSATION	UNIT-BASED COMPENSATION SMLP Long-Term Incentive Plan. The 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. In March 2015, we granted 200,283 phantom units to employees in connection with our annual incentive compensation award cycle. These awards had a grant date fair value of $33.94 and vest ratably over a three-year period. As of June 30, 2015, approximately 4.4 million common units remained available for future issuance.

CONCENTRATIONS OF RISK

6 Months Ended

Jun. 30, 2015

Risks and Uncertainties [Abstract]

CONCENTRATIONS OF RISK

Financial instruments that potentially subject us to concentrations of credit risk consist of cash and accounts receivable. We maintain our cash 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.

Counterparties accounting for more than 10% of total revenues were as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
Revenue:
Counterparty A - Piceance Basin	14	%	17	%	14	%	17	%
Counterparty B - Marcellus Shale	10	%	*		10	%	*
Counterparty C - Piceance Basin	*		*		*		*
Counterparty D - Williston Basin – Gas	*		*		*		*

__________

* Less than 10%

Counterparties accounting for more than 10% of total accounts receivable were as follows:



	June 30,		December 31,
	2015		2014
Accounts receivable:
Counterparty A - Piceance Basin	13	%	27	%
Counterparty B - Marcellus Shale	10	%	*
Counterparty C - Piceance Basin	11	%	*
Counterparty D - Williston Basin – Gas	*		13	%

__________

* Less than 10%

RELATED-PARTY TRANSACTIONS

6 Months Ended

Jun. 30, 2015

RELATED-PARTY TRANSACTIONS

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. Due to affiliate 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 June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Operation and maintenance expense	$	5,586	$	5,200	$	11,367	$	9,570
General and administrative expense	5,534		5,768		11,327		11,640

Expenses Incurred by Summit Investments. Prior to the Polar and Divide Drop Down and the Red Rock Drop Down, Summit Investments incurred:


•	certain support expenses and capital expenditures on behalf of the contributed subsidiaries. These transactions were settled periodically through membership interests prior to the respective drop down and


•	interest expense that was related to capital projects for the contributed subsidiaries. As such, the associated interest expense was allocated to the respective contributed subsidiary's capital projects as a noncash contribution and capitalized into the basis of the asset.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

COMMITMENTS AND CONTINGENCIES

6 Months Ended

Jun. 30, 2015

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

Operating Leases. Rent expense related to operating leases, including rent expense incurred on our behalf and allocated to us by Summit Investments, was as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Rent expense	$	556	$	467	$	983	$	849

Environmental Matters. There are no material liabilities related to environmental remediation costs, arising from claims, assessments, litigation, fines, or penalties and other sources in the accompanying financial statements at June 30, 2015 or December 31, 2014. However, we can provide no assurance that significant costs and liabilities will not be incurred in the future. We are currently not aware of any material contingent liabilities that exist with respect to environmental matters.

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 its financial position or results of operations.

ACQUISITIONS AND DROP DOWN TRANSACTIONS

6 Months Ended

Jun. 30, 2015

Business Combinations [Abstract]

Acquisitions and Drop Down Transactions

ACQUISITIONS AND DROP DOWN TRANSACTIONS

Polar and Divide Drop Down. On May 18, 2015, we acquired Polar Midstream and Epping from a subsidiary of Summit Investments, subject to customary working capital and capital expenditures adjustments. Due to the concurrent timing of acquiring Polar Midstream and Epping, we have aggregated these purchases into the Polar and Divide Drop Down. We funded the initial combined purchase price of $290.0 million with (i) $92.5 million of borrowings under our revolving credit facility and (ii) the issuance of $193.4 million of SMLP common units and $4.1 million of general partner interests to SMLP’s general partner in connection with the May 2015 Equity Offering.

Red Rock Drop Down. On March 18, 2014, we acquired Red Rock Gathering from a subsidiary of Summit Investments, subject to customary working capital adjustments. The Partnership paid total cash consideration of $307.9 million, comprising $305.0 million at the date of acquisition and $2.9 million of working capital adjustments that were recognized in due to affiliate as of December 31, 2014 and settled in February 2015.

Supplemental Disclosures – As-If Pooled Basis. As a result of accounting for our drop down transactions similar to a pooling of interests, our historical financial statements and those of Polar Midstream, Epping and Red Rock Gathering have been combined to reflect the historical operations, financial position and cash flows from the date common control began. Revenues and net income for the previously separate entities and the combined amounts, as presented in these consolidated financial statements follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
SMLP revenues	$	72,583	$	80,796	$	141,162	$	145,685
Polar and Divide revenues	4,691		5,188		13,273		8,367
Red Rock Gathering revenues (1)							11,313
Combined revenues	$	77,274	$	85,984	$	154,435	$	165,365

SMLP net income	$	2,985	$	4,036	$	4,652	$	7,581
Polar and Divide net income	2,057		1,586		5,403		1,138
Red Rock Gathering net income (1)							2,828
Combined net income	$	5,042	$	5,622	$	10,055	$	11,547

__________

(1) Results are fully reflected in SMLP's revenues and net income subsequent to March 2014.

- Definition

The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1497-128463

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1490-128463

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e7008-128479

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1486-128463

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 805
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

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-Name Accounting Standards Codification
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-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1500-128463

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1524-128463

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e7000-128479

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4922-128472

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4934-128472

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4926-128472

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1383-128463

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
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-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6996-128479

+ Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Jun. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	Presentation and Consolidation. We prepare our unaudited condensed consolidated financial statements in accordance with accounting principles generally accepted in the United States of America ("GAAP"). These principles are established by the Financial Accounting Standards Board (the "FASB"). The unaudited condensed consolidated financial statements include the assets, liabilities, and results of operations of SMLP and its subsidiaries. All intercompany transactions among the consolidated entities have been eliminated in consolidation. 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 Securities and Exchange Commission (the "SEC"). Certain information and note disclosures normally included in 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 accruals, which are necessary to fairly present the unaudited condensed consolidated balance sheet as of June 30, 2015, the unaudited condensed consolidated statements of operations for the three- and six-month periods ended June 30, 2015 and 2014, and the unaudited condensed consolidated statements of partners' capital and cash flows for the six-month periods ended June 30, 2015 and 2014. 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, 2014 as filed with the SEC on March 2, 2015 (the "2014 Annual Report"). The results of operations for an interim period are not necessarily indicative of results expected for a full year.
Acquisitions	SMLP recognized its acquisitions of (i) Polar Midstream and Epping and (ii) Red Rock Gathering (the "Red Rock Drop Down") at Summit Investments' historical cost of construction or fair value of assets and liabilities at acquisition because the acquisitions were executed by entities under common control. The excess of Summit Investments' net investment in Polar Midstream and Epping was recognized as an addition to partners' capital. The excess of the purchase price paid by SMLP over Summit Investments' net investment in Red Rock Gathering was recognized as a reduction to partners' capital. Due to the common control aspect, the Polar and Divide Drop Down and the Red Rock Drop Down were accounted for by the Partnership on an “as-if pooled” basis for the periods during which common control existed. For the purposes of these unaudited condensed consolidated financial statements, SMLP's results of operations reflect the results of operations of Polar Midstream, Epping and Red Rock Gathering for all periods presented.
Comprehensive Income	Comprehensive Income. Comprehensive income is the same as net income for all periods presented.
Environmental Matters	Environmental Matters. We are subject to various federal, state and local laws and regulations relating to the protection of the environment. Liabilities for loss contingencies, including environmental remediation costs, arising from claims, assessments, litigation, fines, and penalties and other sources are charged to expense when it is probable that a liability has been incurred and the amount of the assessment and/or remediation can be reasonably estimated. We accrue for losses associated with environmental remediation obligations when such losses are probable and reasonably estimable. Such accruals are adjusted as further information develops or circumstances change. Recoveries of environmental remediation costs from other parties or insurers are recorded as assets when their receipt is deemed probable.
Recent Accounting Pronouncements	Recent Accounting Pronouncements. Accounting standard setters frequently issue new or revised accounting rules. We review new pronouncements to determine the impact, if any, on our financial statements. There are currently no recent pronouncements that have been issued that we believe may materially affect our financial statements, except as noted below. In May 2014, the FASB released a joint revenue recognition standard, Accounting Standards Update ("ASU") No. 2014-09 Revenue From Contracts With Customers (Topic 606) ("ASU 2014-09"). Under ASU 2014-09, revenue will be recognized under a five-step model: (i) identify the contract with the customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to performance obligations; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. In its original form, ASU 2014-09 was effective for fiscal years, and interim periods within those years, beginning after December 15, 2016; early adoption was not permitted. In July 2015, the FASB reaffirmed the guidance in its April 2015 proposed ASU that defers for one year the effective date of the ASU 2014-09 for both public and nonpublic entities reporting under U.S. GAAP and allows early adoption as of the original effective date. We are currently in the process of evaluating the impact of this update. In February 2015, the FASB issued ASU No. 2015-02—Consolidation (Topic 810): Amendments to the Consolidation Analysis ("ASU 2015-02"). The standard changes the analysis that a reporting entity must perform to determine whether it should consolidate certain types of legal entities. This new standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015, and interim and annual periods thereafter. Early adoption is permitted. We are currently in the process of evaluating the impact of this update. In April 2015, the FASB issued ASU No. 2015-03—Interest—Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs ("ASU 2015-03"). Under ASU 2015-03, entities that have historically presented debt issuance costs as an asset, related to a recognized debt liability, will be required to present those costs as a direct deduction from the carrying amount of that debt liability. This presentation will result in debt issuance cost being presented the same way debt discounts have historically been handled. This new standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015, and interim and annual periods thereafter. Early adoption is permitted. We are currently in the process of evaluating the impact of this update.

SEGMENT INFORMATION (Tables)

6 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

Schedule of assets by reportable segment

Assets by reportable segment follow.



	June 30,		December 31,
	2015		2014
	(In thousands)
Assets:
Marcellus Shale	$	239,384	$	243,884
Williston Basin – Gas	294,725		311,041
Williston Basin – Liquids	431,951		398,847
Barnett Shale	424,706		428,935
Piceance Basin	833,385		872,437
Total reportable segment assets	2,224,151		2,255,144
Corporate	34,602		38,577
Total assets	$	2,258,753	$	2,293,721

Schedule of segment reporting information

Segment adjusted EBITDA by reportable segment follows.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Reportable segment adjusted EBITDA:
Marcellus Shale	$	6,162	$	3,837	$	12,696	$	7,721
Williston Basin – Gas	4,740		4,809		10,075		9,485
Williston Basin – Liquids	6,497		2,626		11,540		3,000
Barnett Shale	15,540		14,958		32,301		29,991
Piceance Basin	26,864		26,780		54,099		52,361
Total reportable segment adjusted EBITDA	$	59,803	$	53,010	$	120,711	$	102,558

Revenues by reportable segment follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Revenues:
Marcellus Shale	$	7,783	$	5,665	$	15,622	$	11,021
Williston Basin – Gas	7,454		14,819		16,364		31,582
Williston Basin – Liquids	9,906		5,188		18,487		8,367
Barnett Shale	23,823		24,241		47,720		47,277
Piceance Basin	28,308		36,071		56,242		67,118
Total reportable segment revenues and total revenues	$	77,274	$	85,984	$	154,435	$	165,365

Depreciation and amortization by reportable segment follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Depreciation and amortization:
Marcellus Shale	$	2,169	$	1,861	$	4,338	$	3,661
Williston Basin – Gas	4,778		4,488		9,476		8,737
Williston Basin – Liquids	1,735		955		3,347		1,692
Barnett Shale	3,902		3,739		7,808		7,376
Piceance Basin	11,210		10,250		22,414		20,063
Total reportable segments	23,794		21,293		47,383		41,529
Corporate	184		142		350		285
Total depreciation and amortization	$	23,978	$	21,435	$	47,733	$	41,814

Capital expenditures by reportable segment follow.



	Six months ended June 30,
	2015		2014
	(In thousands)
Capital expenditures:
Marcellus Shale	$	637	$	10,969
Williston Basin – Gas	8,699		21,884
Williston Basin – Liquids	38,790		24,697
Barnett Shale	1,922		9,856
Piceance Basin	9,734		20,564
Total reportable segments	59,782		87,970
Corporate	393		63
Total capital expenditures	$	60,175	$	88,033

Reconciliation of net income to adjusted EBITDA

A reconciliation of income before income taxes to total reportable segment adjusted EBITDA follows.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Reconciliation of Income Before Income Taxes to Segment Adjusted EBITDA:
Income before income taxes	$	4,937	$	6,091	$	10,127	$	12,175
Add:
Interest expense	12,083		10,803		24,201		17,947
Depreciation and amortization	24,190		21,660		48,196		42,265
Adjustments related to MVC shortfall payments	10,928		10,577		23,268		22,590
Unit-based compensation	1,737		1,446		3,134		2,594
Loss on asset sales	—		6		—		6
Allocated corporate expenses	6,142		2,428		12,000		4,983
Less:
Interest income	—		1		1		2
Gain on asset sales	214		—		214		—
Total reportable segment adjusted EBITDA	$	59,803	$	53,010	$	120,711	$	102,558

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on property, plant, and equipment, net follow.



	Useful lives (In years)	June 30,		December 31,
	Useful lives (In years)	2015		2014
		(Dollars in thousands)
Gathering and processing systems and related equipment	30	$	1,510,375	$	1,462,706
Construction in progress	n/a	48,226		44,447
Other	4-15	29,360		28,871
Total		1,587,961		1,536,024
Less accumulated depreciation		149,163		121,674
Property, plant, and equipment, net		$	1,438,798	$	1,414,350

Schedule of depreciation expense related to property, plant and equipment and capitalized interest

Depreciation expense and capitalized interest were as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Depreciation expense	$	13,851	$	12,000	$	27,489	$	23,197
Capitalized interest	1,003		2,388		1,651		4,019

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT (Tables)

6 Months Ended

Jun. 30, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets and liabilities subject to amortization

Details regarding our intangible assets and the unfavorable gas gathering contract, all of which are subject to amortization, follow.



	June 30, 2015
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(8,857	)	$	15,338
Contract intangibles	12.5	426,464		(93,383		)	333,081
Rights-of-way	24.3	125,517		(15,311		)	110,206
Total intangible assets		$	576,176	$	(117,551	)	$	458,625

Unfavorable gas gathering contract	10.0	$	10,962	$	(5,723	)	$	5,239



	December 31, 2014
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(8,056	)	$	16,139
Contract intangibles	12.5	426,464		(75,713		)	350,751
Rights-of-way	24.7	123,581		(12,737		)	110,844
Total intangible assets		$	574,240	$	(96,506	)	$	477,734

Unfavorable gas gathering contract	10.0	$	10,962	$	(5,385	)	$	5,577

Recognized amortization expense in other revenues and cost and expenses

We recognized amortization expense in other revenues as follows:



	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(375	)	$	(436	)	$	(801	)	$	(870	)
Amortization expense – unfavorable gas gathering contract	163			211			338			419

We recognized amortization expense in costs and expenses as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Amortization expense – contract intangibles	$	8,835	$	8,198	$	17,670	$	16,160
Amortization expense – rights-of-way	1,293		1,239		2,574		2,457

Estimated aggregate annual amortization expected to be recognized

The estimated aggregate annual amortization expected to be recognized for the remainder of 2015 and each of the four succeeding fiscal years follows.



	Intangible assets		Unfavorable gas gathering contract
	(In thousands)
2015	$	21,135	$	368
2016	42,288		924
2017	41,139		1,047
2018	40,593		1,035
2019	40,838		1,045

DEFERRED REVENUE (Tables)

6 Months Ended

Jun. 30, 2015

Deferred Revenue Disclosure [Abstract]

Rollforward of deferred revenue

A rollforward of current deferred revenue follows.



	Williston Basin - Gas		Barnett Shale		Piceance Basin		Total current
	(In thousands)
Current deferred revenue, January 1, 2015	$	—	$	2,377	$	—	$	2,377
Additions	—		999		—		999
Less: revenue recognized	—		2,699		—		2,699
Current deferred revenue, June 30, 2015	$	—	$	677	$	—	$	677

A rollforward of noncurrent deferred revenue follows.



	Williston Basin - Gas		Barnett Shale		Piceance Basin		Total noncurrent
	(In thousands)
Noncurrent deferred revenue, January 1, 2015	$	17,132	$	—	$	38,107	$	55,239
Additions	—		—		7,572		7,572
Less: revenue recognized	27		—		—		27
Noncurrent deferred revenue, June 30, 2015	$	17,105	$	—	$	45,679	$	62,784

LONG-TERM DEBT (Tables)

6 Months Ended

Jun. 30, 2015

Debt Disclosure [Abstract]

Schedule of long-term debt instruments

Long-term debt consisted of the following:



	June 30,		December 31,
	2015		2014
	(In thousands)
Variable rate senior secured revolving credit facility (2.44% at June 30, 2015 and 2.67% at December 31, 2014) due November 2018	$	279,000	$	208,000
5.50% Senior unsecured notes due August 2022	300,000		300,000
7.50% Senior unsecured notes due July 2021	300,000		300,000
Total long-term debt	$	879,000	$	808,000

Summary of the estimated fair value of debt instruments

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



	June 30, 2015				December 31, 2014
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Revolving credit facility	$	279,000	$	279,000	$	208,000	$	208,000
5.5% Senior notes	300,000		286,500		300,000		281,750
7.5% Senior notes	300,000		313,250		300,000		306,750

- 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=6928386&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=6479336&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=34725769&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=6928386&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=6928386&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=6451184&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=6451184&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=6928386&loc=d3e21521-112644

+ Details

PARTNERS' CAPITAL (Tables)

6 Months Ended

Jun. 30, 2015

Limited Partners' Capital Account [Line Items]

Schedule of Partner Units Activity

A rollforward of the number of common limited partner, subordinated limited partner and general partner units follows.



	Common	Subordinated	General partner	Total
Units, January 1, 2015	34,426,513	24,409,850	1,200,651	60,037,014
Units issued in connection with the May 2015 Equity Offering (1)	7,475,000	—	152,551	7,627,551
Units issued under SMLP LTIP (2)	70,580	—	1,498	72,078
Units, June 30, 2015	41,972,093	24,409,850	1,354,700	67,736,643

__________

(1) Including issuance to general partner in connection with contributions made to maintain 2% general partner interest.

(2) Net of 19,702 units withheld to meet minimum statutory tax withholding requirements

Details of Cash Distributions

Details of cash distributions declared in 2015 follow.



Attributable to the quarter ended	Payment date	Per-unit distribution		Cash paid to common unitholders		Cash paid to subordinated unitholders		Cash paid to general partner		Cash paid for IDRs		Total distribution
		(In thousands, except per-unit amounts)
December 31, 2014	February 13, 2015	$	0.5600	$	19,279	$	13,670	$	702	$	1,442	$	35,093
March 31, 2015	May 15, 2015	$	0.5650	$	19,490	$	13,792	$	710	$	1,534	$	35,526

Polar Midstream and Epping

Limited Partners' Capital Account [Line Items]

Allocation of Capital Contribution from Acquisition [Table Text Block]

The calculation of the capital contribution and its allocation to partners' capital follow (dollars in thousands).



Summit Investments' net investment in Polar Midstream and Epping			$	416,044
Total cash consideration paid to a subsidiary of Summit Investments			290,000
Excess of acquired carrying value over consideration paid			$	126,044

Allocation of capital contribution:
General partner interest	$	2,521
Common limited partner interest	77,423
Subordinated limited partner interest	46,100
Partners' capital contribution – excess of acquired carrying value over consideration paid			$	126,044

Red Rock Gathering Company, LLC

Limited Partners' Capital Account [Line Items]

Calculation of capital distribution and its allocation to partners' capital

The calculation of the capital distribution and its allocation to partners' capital follow (dollars in thousands).



Summit Investments' net investment in Red Rock Gathering				$	241,817
Total cash consideration paid to a subsidiary of Summit Investments				307,941
Excess of consideration paid over acquired carrying value				$	(66,124	)

Allocation of capital distribution:
General partner interest	$	(1,323	)
Common limited partner interest	(37,910		)
Subordinated limited partner interest	(26,891		)
Partners' capital distribution – excess of consideration paid over acquired carrying value				$	(66,124	)

EARNINGS PER UNIT (Tables)

6 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

Schedule of earnings per limited partner unit

The following table details the components of earnings per limited partner unit.



	Three months ended June 30,					Six months ended June 30,
	2015			2014		2015			2014
	(In thousands, except per-unit amounts)
Numerator for basic and diluted EPU:
Allocation of net income among limited partner interests:
Net income attributable to common units	$	1,847		$	1,891	$	1,490		$	4,398
Net (loss) income attributable to subordinated units	(753		)	1,344		(297		)	1,951
Net income attributable to limited partners	$	1,094		$	3,235	$	1,193		$	6,349

Denominator for basic and diluted EPU:
Weighted-average common units outstanding – basic	38,278			34,422		36,369			32,179
Effect of nonvested phantom units	183			197		108			181
Weighted-average common units outstanding – diluted	38,461			34,619		36,477			32,360

Weighted-average subordinated units outstanding – basic and diluted	24,410			24,410		24,410			24,410

Earnings (loss) per limited partner unit:
Common unit – basic	$	0.05		$	0.05	$	0.04		$	0.14
Common unit – diluted	$	0.05		$	0.05	$	0.04		$	0.14
Subordinated unit – basic and diluted	$	(0.03	)	$	0.05	$	(0.01	)	$	0.08

CONCENTRATIONS OF RISK (Tables)

6 Months Ended

Jun. 30, 2015

Revenue | Customer concentration

CONCENTRATIONS OF RISK

Schedule of customers accounting for more than 10% of total revenues and accounts receivable

Counterparties accounting for more than 10% of total revenues were as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
Revenue:
Counterparty A - Piceance Basin	14	%	17	%	14	%	17	%
Counterparty B - Marcellus Shale	10	%	*		10	%	*
Counterparty C - Piceance Basin	*		*		*		*
Counterparty D - Williston Basin – Gas	*		*		*		*

__________

* Less than 10%

Accounts receivable | Credit concentration

CONCENTRATIONS OF RISK

Schedule of customers accounting for more than 10% of total revenues and accounts receivable

Counterparties accounting for more than 10% of total accounts receivable were as follows:



	June 30,		December 31,
	2015		2014
Accounts receivable:
Counterparty A - Piceance Basin	13	%	27	%
Counterparty B - Marcellus Shale	10	%	*
Counterparty C - Piceance Basin	11	%	*
Counterparty D - Williston Basin – Gas	*		13	%

__________

* Less than 10%

RELATED-PARTY TRANSACTIONS (Tables)

6 Months Ended

Jun. 30, 2015

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 June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Operation and maintenance expense	$	5,586	$	5,200	$	11,367	$	9,570
General and administrative expense	5,534		5,768		11,327		11,640

COMMITMENTS AND CONTINGENCIES (Tables)

6 Months Ended

Jun. 30, 2015

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 by Summit Investments, was as follows:



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
Rent expense	$	556	$	467	$	983	$	849

ACQUISITIONS AND DROP DOWN TRANSACTIONS (Tables)

6 Months Ended

Jun. 30, 2015

Business Combinations [Abstract]

Schedule of Revenue and Net Income Disclosures

Revenues and net income for the previously separate entities and the combined amounts, as presented in these consolidated financial statements follow.



	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
	(In thousands)
SMLP revenues	$	72,583	$	80,796	$	141,162	$	145,685
Polar and Divide revenues	4,691		5,188		13,273		8,367
Red Rock Gathering revenues (1)							11,313
Combined revenues	$	77,274	$	85,984	$	154,435	$	165,365

SMLP net income	$	2,985	$	4,036	$	4,652	$	7,581
Polar and Divide net income	2,057		1,586		5,403		1,138
Red Rock Gathering net income (1)							2,828
Combined net income	$	5,042	$	5,622	$	10,055	$	11,547

ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	May 22, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
ORGANIZATION AND BUSINESS OPERATIONS
Common limited partner capital, units outstanding		41,972,000		41,972,000		34,427,000
Cost of natural gas and NGLs		$ 4,905	$ 15,118	$ 10,289	$ 29,473
Reclassification Adjustment \| Williston Basin – Gas Segment \| Operating and Maintenance
ORGANIZATION AND BUSINESS OPERATIONS
Cost of natural gas and NGLs		$ 1,000	$ 1,300	$ 2,700	$ 2,200
Common units \| SMP Holdings
ORGANIZATION AND BUSINESS OPERATIONS
Common limited partner capital, units outstanding		5,293,571		5,293,571
General partner
ORGANIZATION AND BUSINESS OPERATIONS
General partner interest (as a percent)	2.00%			2.00%

SEGMENT INFORMATION - Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Assets	$ 2,258,753	$ 2,293,721
Reportable Segments
Segment Reporting Information [Line Items]
Assets	2,224,151	2,255,144
Reportable Segments \| Marcellus Shale Segment
Segment Reporting Information [Line Items]
Assets	239,384	243,884
Reportable Segments \| Williston Basin – Gas Segment
Segment Reporting Information [Line Items]
Assets	294,725	311,041
Reportable Segments \| Williston Basin – Liquids Segment
Segment Reporting Information [Line Items]
Assets	431,951	398,847
Reportable Segments \| Barnett Shale Segment
Segment Reporting Information [Line Items]
Assets	424,706	428,935
Reportable Segments \| Piceance Basin Segment
Segment Reporting Information [Line Items]
Assets	833,385	872,437
Corporate
Segment Reporting Information [Line Items]
Assets	$ 34,602	$ 38,577

SEGMENT INFORMATION - Revenues, Depreciation and Amortization, and Capital Expenditures by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 77,274	$ 85,984	$ 154,435	$ 165,365
Depreciation and amortization	23,978	21,435	47,733	41,814
Capital expenditures			60,175	88,033
Reportable Segments
Segment Reporting Information [Line Items]
Revenues	77,274	85,984	154,435	165,365
Depreciation and amortization	23,794	21,293	47,383	41,529
Capital expenditures			59,782	87,970
Reportable Segments \| Marcellus Shale Segment
Segment Reporting Information [Line Items]
Revenues	7,783	5,665	15,622	11,021
Depreciation and amortization	2,169	1,861	4,338	3,661
Capital expenditures			637	10,969
Reportable Segments \| Williston Basin – Gas Segment
Segment Reporting Information [Line Items]
Revenues	7,454	14,819	16,364	31,582
Depreciation and amortization	4,778	4,488	9,476	8,737
Capital expenditures			8,699	21,884
Reportable Segments \| Williston Basin – Liquids Segment
Segment Reporting Information [Line Items]
Revenues	9,906	5,188	18,487	8,367
Depreciation and amortization	1,735	955	3,347	1,692
Capital expenditures			38,790	24,697
Reportable Segments \| Barnett Shale Segment
Segment Reporting Information [Line Items]
Revenues	23,823	24,241	47,720	47,277
Depreciation and amortization	3,902	3,739	7,808	7,376
Capital expenditures			1,922	9,856
Reportable Segments \| Piceance Basin Segment
Segment Reporting Information [Line Items]
Revenues	28,308	36,071	56,242	67,118
Depreciation and amortization	11,210	10,250	22,414	20,063
Capital expenditures			9,734	20,564
Corporate
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 184	$ 142	350	285
Capital expenditures			$ 393	$ 63

SEGMENT INFORMATION - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Income before income taxes	$ 4,937	$ 6,091	$ 10,127	$ 12,175
Add:
Interest expense	12,083	10,803	24,201	17,947
Depreciation and amortization	24,190	21,660	48,196	42,265
Adjustments related to MVC shortfall payments	10,928	10,577	23,268	22,590
Unit-based compensation	1,737	1,446	3,134	2,594
Loss on asset sales	(214)	6	(214)	6
Less:
Interest income	0	1	1	2
Gain on asset sales	214	(6)	214	(6)
Corporate
Add:
Allocated corporate expenses	6,142	2,428	12,000	4,983
Reportable Segments
Less:
Total reportable segment adjusted EBITDA	$ 59,803	$ 53,010	$ 120,711	$ 102,558

SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - Reportable Segments - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 59,803	$ 53,010	$ 120,711	$ 102,558
Marcellus Shale Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,162	3,837	12,696	7,721
Williston Basin – Gas Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	4,740	4,809	10,075	9,485
Williston Basin – Liquids Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,497	2,626	11,540	3,000
Barnett Shale Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	15,540	14,958	32,301	29,991
Piceance Basin Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 26,864	$ 26,780	$ 54,099	$ 52,361

PROPERTY, PLANT, AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Gross	$ 1,587,961		$ 1,587,961		$ 1,536,024
Less: accumulated depreciation	149,163		149,163		121,674
Property, plant, and equipment, net	1,438,798		1,438,798		1,414,350
Depreciation expense	13,851	$ 12,000	27,489	$ 23,197
Capitalized interest	1,003	$ 2,388	$ 1,651	$ 4,019
Gathering and processing systems and related equipment
Property, Plant and Equipment [Line Items]
Useful lives			30 years
Gross	1,510,375		$ 1,510,375		1,462,706
Construction in progress
Property, Plant and Equipment [Line Items]
Gross	48,226		48,226		44,447
Other
Property, Plant and Equipment [Line Items]
Gross	$ 29,360		$ 29,360		$ 28,871
Other \| Minimum
Property, Plant and Equipment [Line Items]
Useful lives			4 years
Other \| Maximum
Property, Plant and Equipment [Line Items]
Useful lives			15 years

AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 576,176		$ 576,176		$ 574,240
Accumulated amortization	(117,551)		(117,551)		(96,506)
Total intangible assets, net	458,625		$ 458,625		$ 477,734
Noncurrent liability
Unfavorable gas gathering contract, useful lives			10 years		10 years
Unfavorable contract, Gross Carrying Amount	10,962		$ 10,962		$ 10,962
Unfavorable gas gathering contract, Accumulated Amortization	(5,723)		(5,723)		(5,385)
Unfavorable gas gathering contract, Net	5,239		5,239		$ 5,577
Amortization expense
Amortization expense - unfavorable contract	163	$ 211	338	$ 419
Intangible assets
2015	21,135		21,135
2016	42,288		42,288
2017	41,139		41,139
2018	40,593		40,593
2019	40,838		40,838
Unfavorable gas gathering contract
2015	368		368
2016	924		924
2017	1,047		1,047
2018	1,035		1,035
2019	1,045		$ 1,045
Favorable gas gathering contract
Finite-Lived Intangible Assets [Line Items]
Useful lives			18 years 8 months 12 days		18 years 8 months 12 days
Gross carrying amount	24,195		$ 24,195		$ 24,195
Accumulated amortization	(8,857)		(8,857)		(8,056)
Total intangible assets, net	15,338		15,338		$ 16,139
Amortization expense
Amortization expense	375	436	$ 801	870
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Useful lives			12 years 6 months		12 years 6 months
Gross carrying amount	426,464		$ 426,464		$ 426,464
Accumulated amortization	(93,383)		(93,383)		(75,713)
Total intangible assets, net	333,081		333,081		$ 350,751
Amortization expense
Amortization expense	8,835	8,198	$ 17,670	16,160
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Useful lives			24 years 3 months		24 years 8 months
Gross carrying amount	125,517		$ 125,517		$ 123,581
Accumulated amortization	(15,311)		(15,311)		(12,737)
Total intangible assets, net	110,206		110,206		$ 110,844
Amortization expense
Amortization expense	$ 1,293	$ 1,239	$ 2,574	$ 2,457

GOODWILL (Details) - USD ($)	3 Months Ended	6 Months Ended
GOODWILL (Details) - USD ($)	Dec. 31, 2014	Jun. 30, 2015	Sep. 30, 2014
Goodwill [Line Items]
Goodwill impairment	$ 54,200,000	$ 0
Goodwill	$ 265,062,000	$ 265,062,000
Williston Basin – Liquids Segment
Goodwill [Line Items]
Goodwill			$ 203,400,000

DEFERRED REVENUE (Details) $ in Thousands	6 Months Ended
DEFERRED REVENUE (Details) $ in Thousands	Jun. 30, 2015 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 2,377
Additions	999
Less: revenue recognized	2,699
Current deferred revenue, ending balance	677
Noncurrent deferred revenue, beginning balance	55,239
Additions	7,572
Less: revenue recognized	27
Noncurrent deferred revenue, ending balance	62,784
Shortfall payments billed and included in accounts receivable	$ 3,200
Maximum period customers have the ability to offset their gathering fees	6 years
Williston Basin – Gas Segment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 0
Additions	0
Less: revenue recognized	0
Current deferred revenue, ending balance	0
Noncurrent deferred revenue, beginning balance	17,132
Additions	0
Less: revenue recognized	27
Noncurrent deferred revenue, ending balance	17,105
Barnett Shale Segment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	2,377
Additions	999
Less: revenue recognized	2,699
Current deferred revenue, ending balance	677
Noncurrent deferred revenue, beginning balance	0
Additions	0
Less: revenue recognized	0
Noncurrent deferred revenue, ending balance	0
Piceance Basin Segment
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Additions	0
Less: revenue recognized	0
Current deferred revenue, ending balance	0
Noncurrent deferred revenue, beginning balance	38,107
Additions	7,572
Less: revenue recognized	0
Noncurrent deferred revenue, ending balance	$ 45,679

LONG-TERM DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Revolving credit facility	$ 279,000	$ 208,000
Total long-term debt	$ 879,000	$ 808,000
Revolving credit facility
Line of Credit Facility [Line Items]
Weighted-average interest rate (as a percent)	2.44%	2.67%
5.5% Senior Notes
Line of Credit Facility [Line Items]
Senior unsecured notes	$ 300,000	$ 300,000
7.5% Senior Notes
Line of Credit Facility [Line Items]
Senior unsecured notes	$ 300,000	$ 300,000
Senior Notes \| 5.5% Senior Notes
Line of Credit Facility [Line Items]
Stated interest rate	5.50%	5.50%
Senior Notes \| 7.5% Senior Notes
Line of Credit Facility [Line Items]
Stated interest rate	7.50%	7.50%

LONG-TERM DEBT - Additional Disclosures (Details) - USD ($)	1 Months Ended
	Jul. 31, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2013
5.5% Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes		$ 300,000,000	$ 300,000,000
7.5% Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes		300,000,000	$ 300,000,000
Senior Notes
Debt Instrument [Line Items]
Debt defaults		$ 0
Senior Notes \| 5.5% Senior Notes
Debt Instrument [Line Items]
Stated interest rate		5.50%	5.50%
Senior Notes \| 7.5% Senior Notes
Debt Instrument [Line Items]
Stated interest rate		7.50%	7.50%
Revolving credit facility
Debt Instrument [Line Items]
Borrowing capacity		$ 700,000,000.0
Debt defaults		0
Revolving credit facility \| Accordion provision
Debt Instrument [Line Items]
Borrowing capacity		$ 200,000,000.0
Finance Corp.
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary	100.00%
Summit Holdings and Finance Corporation \| Senior Notes \| 5.5% Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes	$ 300,000,000.0
Stated interest rate	5.50%
Summit Holdings and Finance Corporation \| Senior Notes \| 7.5% Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes				$ 300,000,000.0
Stated interest rate				7.50%

LONG-TERM DEBT - Fair Value of Debt Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Revolving credit facility, Carrying value	$ 279,000	$ 208,000
Fair value, Level 2 inputs
Debt Instrument [Line Items]
Revolving credit facility, Estimated fair value (Level 2)	279,000	208,000
5.5% Senior Notes
Debt Instrument [Line Items]
Senior notes, Carrying value	300,000	300,000
5.5% Senior Notes \| Fair value, Level 2 inputs
Debt Instrument [Line Items]
Senior notes, Estimated fair value (Level 2)	286,500	281,750
7.5% Senior Notes
Debt Instrument [Line Items]
Senior notes, Carrying value	300,000	300,000
7.5% Senior Notes \| Fair value, Level 2 inputs
Debt Instrument [Line Items]
Senior notes, Estimated fair value (Level 2)	$ 313,250	$ 306,750

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

PARTNERS' CAPITAL - Additional Disclosures (Details) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended	6 Months Ended
	May 22, 2015	May 22, 2015	May 13, 2015	Jun. 30, 2015	Jun. 30, 2015
Schedule of Partners' Capital [Line Items]
Common units sold in public offering					7,627,551
General partner
Schedule of Partners' Capital [Line Items]
General partner interest (as a percent)		2.00%			2.00%
Common
Schedule of Partners' Capital [Line Items]
Common units sold in public offering					7,475,000
Maximum offering price of units for issuance and sale under equity distribution agreement				$ 150.0
Public Offering \| Common
Schedule of Partners' Capital [Line Items]
Common units sold in public offering			6,500,000
Common units sold in public offering, price per share (in dollars per share)			$ 30.75
Over-Allotment Option \| Common
Schedule of Partners' Capital [Line Items]
Common units sold in public offering	975,000
Common units sold in public offering, price per share (in dollars per share)	$ 30.75

PARTNERS' CAPITAL - Partners' Capital and Schedule of Units (Details)	6 Months Ended
	Jun. 30, 2015 shares
Rollforwards of the number of partner units
Units, beginning balance	60,037,014
Units issued in connection with May 2015 Equity Offering	7,627,551
Units issued under SMLP LTIP	72,078
Units, ending balance	67,736,643
Units withheld to meet the minimum statutory tax withholding requirement	19,702
Common
Rollforwards of the number of partner units
Units, beginning balance	34,426,513
Units issued in connection with May 2015 Equity Offering	7,475,000
Units issued under SMLP LTIP	70,580
Units, ending balance	41,972,093
Subordinated
Rollforwards of the number of partner units
Units, beginning balance	24,409,850
Units issued in connection with May 2015 Equity Offering	0
Units issued under SMLP LTIP	0
Units, ending balance	24,409,850
General partner
Rollforwards of the number of partner units
Units, beginning balance	1,200,651
Units issued in connection with May 2015 Equity Offering	152,551
Units issued under SMLP LTIP	1,498
Units, ending balance	1,354,700

PARTNERS' CAPITAL - Allocation of Capital Distributions and Contributions (Details) - USD ($) $ in Thousands					6 Months Ended
	May 18, 2015	May 15, 2015	Feb. 13, 2015	Mar. 18, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition [Line Items]
Partners' capital contribution					$ 4,737	$ 4,235
Partners' capital distribution		$ (35,526)	$ (35,093)		(70,619)	(56,749)
Polar Midstream and Epping
Business Acquisition [Line Items]
Percent of membership interest acquired	100.00%
Total consideration	$ 290,000
Partners' capital contribution	126,044
Red Rock Gathering Company, LLC
Business Acquisition [Line Items]
Percent of membership interest acquired				100.00%
Total consideration				$ 307,941
Partners' capital distribution				(66,124)
General partner
Business Acquisition [Line Items]
Partners' capital contribution					4,737	4,235
Partners' capital distribution					(4,388)	(1,658)
General partner \| Polar Midstream and Epping
Business Acquisition [Line Items]
Partners' capital contribution	2,521
General partner \| Red Rock Gathering Company, LLC
Business Acquisition [Line Items]
Partners' capital distribution				(1,323)
Limited partners, Common
Business Acquisition [Line Items]
Partners' capital distribution					(38,769)	(31,169)
Limited partners, Common \| Polar Midstream and Epping
Business Acquisition [Line Items]
Partners' capital contribution	77,423
Limited partners, Common \| Red Rock Gathering Company, LLC
Business Acquisition [Line Items]
Partners' capital distribution				(37,910)
Limited partners, Subordinated
Business Acquisition [Line Items]
Partners' capital distribution					$ (27,462)	$ (23,922)
Limited partners, Subordinated \| Polar Midstream and Epping
Business Acquisition [Line Items]
Partners' capital contribution	46,100
Limited partners, Subordinated \| Red Rock Gathering Company, LLC
Business Acquisition [Line Items]
Partners' capital distribution				(26,891)
Red Rock Gathering Company, LLC \| Summit Investments
Business Acquisition [Line Items]
Net investment				$ 241,817
Polar Midstream and Epping \| Summit Investments
Business Acquisition [Line Items]
Net investment	$ 416,044

PARTNERS' CAPITAL - Cash Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended
	Jul. 23, 2015	May 15, 2015	Feb. 13, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Distribution Made to Limited Partner [Line Items]
Per-unit distribution (in dollars per unit)		$ 0.565	$ 0.56	$ 0.565	$ 0.50	$ 1.125	$ 0.98
General partner distribution amount		$ 710	$ 702
General partner's IDRs		1,534	1,442
Total distributions		35,526	35,093			$ 70,619	$ 56,749
Subsequent Event
Distribution Made to Limited Partner [Line Items]
Per-unit distribution (in dollars per unit)	$ 0.57
Common units
Distribution Made to Limited Partner [Line Items]
Limited partner distribution amount		19,490	19,279
Subordinated Units
Distribution Made to Limited Partner [Line Items]
Limited partner distribution amount		$ 13,792	$ 13,670

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to limited partners	$ 1,094	$ 3,235	$ 1,193	$ 6,349
Earnings (loss) per limited partner unit:
Antidilutive securities excluded from the calculation of diluted loss per common unit	0	0	94,892	0
Common units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to limited partners	$ 1,847	$ 1,891	$ 1,490	$ 4,398
Weighted-average units outstanding - basic	38,278,000	34,422,000	36,369,000	32,179,000
Less: effect of non-vested phantom units and non-vested restricted units (in units)	183,000	197,000	108,000	181,000
Weighted-average units outstanding – diluted	38,461,000	34,619,000	36,477,000	32,360,000
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.05	$ 0.05	$ 0.04	$ 0.14
Diluted (in dollars per share)	$ 0.05	$ 0.05	$ 0.04	$ 0.14
Subordinated Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to limited partners	$ (753)	$ 1,344	$ (297)	$ 1,951
Weighted-average units outstanding - basic	24,410,000	24,410,000	24,410,000	24,410,000
Weighted-average units outstanding – diluted	24,410,000	24,410,000	24,410,000	24,410,000
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ (0.03)	$ 0.05	$ (0.01)	$ 0.08
Diluted (in dollars per share)	$ (0.03)	$ 0.05	$ (0.01)	$ 0.08

UNIT-BASED COMPENSATION - Additional Disclosures (Details) - $ / shares	1 Months Ended	6 Months Ended
	Mar. 31, 2015	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units available for future issuance		4,400,000
Phantom Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Phantom units granted to employees	200,283
Phantom units granted, grant date fair value (in dollars per share)	$ 33.94
Award vesting period		3 years

CONCENTRATIONS OF RISK (Details)	3 Months Ended		6 Months Ended		12 Months Ended
CONCENTRATIONS OF RISK (Details)	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Counterparty A - Piceance Basin \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage	14.00%	17.00%	14.00%	17.00%
Counterparty A - Piceance Basin \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage			13.00%		27.00%
Counterparty B - Marcellus Shale \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage	10.00%		10.00%
Counterparty B - Marcellus Shale \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage			10.00%
Counterparty C - Piceance Basin \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage			11.00%
Counterparty D - Williston Basin - Gas \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Concentration risk, percentage					13.00%

RELATED-PARTY TRANSACTIONS (Details) - General partner - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operation and maintenance expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 5,586	$ 5,200	$ 11,367	$ 9,570
General and administrative expense
RELATED-PARTY TRANSACTIONS
Expenses from transactions with related party	$ 5,534	$ 5,768	$ 11,327	$ 11,640

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Commitments and Contingencies Disclosure [Abstract]
Total rent expense related to operating leases	$ 556	$ 467	$ 983	$ 849

ACQUISITIONS AND DROP DOWN TRANSACTIONS - Polar and Divide Drop Down (Details) - Polar Midstream and Epping $ in Thousands, shares in Millions	May 18, 2015 USD ($) shares
Business Acquisition [Line Items]
Total consideration \| $	$ 290,000
Liabilities incurred for acquisition \| $	$ 92,500
Common units
Business Acquisition [Line Items]
Number of shares issued for acquisition \| shares	193.4
General Partner Units
Business Acquisition [Line Items]
Number of shares issued for acquisition \| shares	4.1

ACQUISITIONS AND DROP DOWN TRANSACTIONS - Red Rock Gathering (Details) - Red Rock Gathering Company, LLC $ in Thousands	Mar. 18, 2014 USD ($)
Business Acquisition [Line Items]
Cost of acquired entity, purchase price	$ 307,941
Cost of acquired entity, cash paid	305,000
Liabilities incurred for acquisition	$ 2,900

ACQUISITIONS AND DROP DOWN TRANSACTIONS - Revenue and Net Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition [Line Items]
Revenues	$ 77,274	$ 85,984	$ 154,435	$ 165,365
Net income	5,042	5,622	10,055	11,547
Summit Midstream Partners, LP
Business Acquisition [Line Items]
Revenues	72,583	80,796	141,162	145,685
Net income	2,985	4,036	4,652	7,581
Polar Midstream and Epping
Business Acquisition [Line Items]
Revenues	4,691	5,188	13,273	8,367
Net income	$ 2,057	$ 1,586	$ 5,403	1,138
Red Rock Gathering Company, LLC
Business Acquisition [Line Items]
Revenues				11,313
Net income				$ 2,828