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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2013	Oct. 31, 2013
Entity Registrant Name	Summit Midstream Partners, LP
Entity Central Index Key	0001549922
Document Type	10-Q
Document Period End Date	Sep. 30, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Common units
Entity Common Stock, Shares Outstanding		29,079,866
Subordinated Units
Entity Common Stock, Shares Outstanding		24,409,850
General Partner Units
Entity Common Stock, Shares Outstanding		1,091,453

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 15,283	$ 7,895
Accounts receivable	34,911	33,504
Due from affiliate	0	774
Other assets	2,354	2,190
Total current assets	52,548	44,363
Property, plant and equipment, net	957,555	681,993
Intangible assets, net:
Favorable gas gathering contracts	18,348	19,958
Contract intangibles	394,804	229,596
Rights-of-way	51,657	35,986
Total intangible assets, net	464,809	285,540
Goodwill	117,766	45,478
Other noncurrent assets	12,417	6,137
Total assets	1,605,095	1,063,511
Current liabilities:
Trade accounts payable	11,909	15,817
Due to affiliate	430	0
Deferred revenue	1,555	865
Ad valorem taxes payable	5,604	5,455
Interest Payable, Current	6,525	16
Other current liabilities	7,620	4,308
Total current liabilities	33,643	26,461
Long-term debt	565,050	199,230
Noncurrent liability, net (Note 4)	6,604	7,420
Deferred revenue	22,560	10,899
Other noncurrent liabilities	361	254
Total liabilities	628,218	244,264
Commitments and contingencies (Note 11)
Common limited partner capital (29,075,447 units issued and outstanding at September 30, 2013 and 24,412,427 units issued and outstanding at December 31, 2012)	570,260	418,856
Subordinated limited partner capital (24,409,850 units issued and outstanding at September 30, 2013 and December 31, 2012)	383,281	380,169
General partner interests (1,091,453 units issued and outstanding at September 30, 2013 and 996,320 issued and outstanding at December 31, 2012)	23,336	20,222
Total partners' capital	976,877	819,247
Total liabilities and partners' capital	$ 1,605,095	$ 1,063,511

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Common limited partner capital, units issued	29,073,974	24,412,427
Common limited partner capital, units outstanding	29,073,974	24,412,427
Subordinated limited partner capital, units issued	24,409,850	24,409,850
Subordinated limited partner capital, units outstanding	24,409,850	24,409,850
General partner interests, units issued	1,091,453	996,320
General partner interests, units outstanding	1,091,453	996,320

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:
Gathering services and other fees	$ 45,968	$ 37,903	$ 127,098	$ 106,550
Natural gas, NGLs and condensate sales and other	17,392	3,232	47,204	10,290
Amortization of favorable and unfavorable contracts	(264)	(160)	(794)	25
Total revenues	63,096	40,975	173,508	116,865
Costs and expenses:
Operation and maintenance	15,918	14,460	45,467	37,177
Cost of natural gas and NGLs	10,464	0	24,328	0
General and administrative	6,248	5,179	18,198	15,977
Transaction costs	123	1,739	2,549	1,972
Depreciation and amortization	16,426	9,156	43,146	26,135
Total costs and expenses	49,179	30,534	133,688	81,261
Other (expense) income	(112)	2	(110)	8
Interest expense	(6,937)	(2,827)	(11,840)	(5,573)
Affiliated interest expense	0	(13)	0	(5,426)
Income before income taxes	6,868	7,603	27,870	24,613
Income tax expense	(177)	(207)	(579)	(501)
Net income	6,691	$ 7,396	27,291	$ 24,112
Less: net income attributable to SMP Holdings (Note 1)	0		52
Net income attributable to partners	6,691		27,239
Less: net income attributable to general partner	134		545
Net income attributable to limited partners	$ 6,557		$ 26,694
Earnings per common unit – basic (in dollars per unit)	$ 0.12		$ 0.57
Earnings per common unit – diluted (in dollars per unit)	0.12		0.57
Earnings per subordinated unit – basic and diluted (in dollars per unit)	$ 0.12		$ 0.48
Weighted-average common units outstanding – basic (in units)	29,074,743		26,234,042
Weighted-average common units outstanding – diluted (in units)	29,227,041		26,352,234
Weighted-average subordinated units outstanding – basic and diluted (in units)	24,409,850		24,409,850
Cash distributions declared per common unit (in dollars per unit)	$ 0.435		$ 1.265

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS - USD ($) $ in Thousands	Total	Bison Midstream	Mountaineer Midstream	SMLP units	Class B Units	SMP Holdings' equity in Bison Midstream	SMP Holdings' equity in Bison Midstream Bison Midstream	SMP Holdings' equity in Bison Midstream Mountaineer Midstream	SMP Holdings' equity in Bison Midstream SMLP units	SMP Holdings' equity in Bison Midstream Class B Units	Membership interests	Membership interests Bison Midstream	Membership interests Mountaineer Midstream	Membership interests SMLP units	Membership interests Class B Units	Limited partners, Common	Limited partners, Common Bison Midstream	Limited partners, Common SMLP units	Limited partners, Common Class B Units	Limited partners, Subordinated	Limited partners, Subordinated Bison Midstream	Limited partners, Subordinated Mountaineer Midstream	Limited partners, Subordinated SMLP units	Limited partners, Subordinated Class B Units	General partner	General partner Bison Midstream	General partner Mountaineer Midstream	General partner SMLP units	General partner Class B Units
Beginning balance at Dec. 31, 2011	$ 640,818					$ 0					$ 640,818					$ 0				$ 0					$ 0
Members Interest Increase (Decrease) Abstract
Net income	24,112					0					24,112					0				0					0
Unit-based compensation					$ 1,793					$ 0					$ 1,793				$ 0					$ 0					$ 0
Contribution of net assets from SMP Holdings in excess of consideration paid for Bison Midstream	0
Ending balance at Sep. 30, 2012	666,723					0					666,723					0				0					0
Beginning balance at Dec. 31, 2012	819,247					0					0					418,856				380,169					20,222
Members Interest Increase (Decrease) Abstract
Net income	27,291					52					0					13,691				13,003					545
Unit-based compensation				$ 1,970	$ 17				$ 0	$ 0				$ 0	$ 0			$ 1,970	$ 17				$ 0	$ 0				$ 0	$ 0
Repurchase of DFW Net Profits Interests	(11,957)					0					0					(5,859)				(5,859)					(239)
Consolidation of Bison Midstream net assets		$ 303,168					$ 303,168					$ 0					$ 0				$ 0					$ 0
Contribution from SMP Holdings to Bison Midstream		2,229					2,229					0					0				0					0
Units issued to acquire entity		(200,000)	$ 100,000				(248,914)	$ 0				0	$ 0				47,936				0	$ 0				978	$ 2,000
Contribution of net assets from SMP Holdings in excess of consideration paid for Bison Midstream	56,535	$ 0					$ (56,535)					$ 0					$ 28,558				$ 26,846					$ 1,131
Distributions to unitholders	(65,088)					0					0					(32,909)				(30,878)					(1,301)
Ending balance at Sep. 30, 2013	$ 976,877					$ 0					$ 0					$ 570,260				$ 383,281					$ 23,336

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 27,291	$ 24,112
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	43,146	26,135
Amortization of favorable and unfavorable contracts	794	(25)
Amortization of deferred loan costs	1,591	1,018
Unit-based compensation	1,987	1,793
Loss on asset sales	113	0
Loss on asset sales	0	5,426
Changes in operating assets and liabilities:
Accounts receivable	4,198	1,522
Due to/from affiliate	1,204	0
Other assets	(147)	(286)
Trade accounts payable	(563)	(5,250)
Change in deferred revenue	9,561	7,585
Ad valorem taxes payable	64	4,050
Accrued interest	6,509	(396)
Other current liabilities	51	2,224
Other noncurrrent liabilities	107	0
Net cash provided by operating activities	95,906	67,908
Cash flows from investing activities:
Capital expenditures	62,317	60,647
Proceeds from asset sales	585	0
Net cash used in investing activities	(471,732)	(60,647)
Cash flows from financing activities:
Distributions to unitholders	(65,088)	0
Borrowings under revolving credit facility	360,000	213,000
Repayments of Lines of Credit	(294,180)	(15,770)
Proceeds from Issuance of Senior Long-term Debt	300,000	0
Proceeds from Other Equity	2,229	0
Proceeds from Issuance of Common Limited Partners Units	100,000	0
Repurchase of DFW Net Profits Interests	(11,957)	0
Deferred loan costs and initial public offering costs	(7,790)	(5,976)
Repayments of Notes Payable	0	(209,230)
Net cash provided by (used in) financing activities	383,214	(17,976)
Net change in cash and cash equivalents	7,388	(10,715)
Cash and cash equivalents, beginning of period	7,895	15,462
Cash and cash equivalents, end of period	15,283	4,747
Supplemental Schedule of Investing and Financing Activities:
Cash interest paid	6,548	6,274
Capitalized interest	2,808	2,191
Interest paid (net of capitalized interest)	3,740	4,083
Cash paid for taxes	660	650
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES
Capital expenditures in accounts payable (period end accruals)	2,592	3,682
Unit-based compensation	1,987	1,793
Issuance of units to partially fund the Bison Drop Down	48,914	0
Contribution of net assets from SMP Holdings in excess of consideration paid for Bison Midstream	56,535	0
Pay-in-kind interest on promissory notes payable to Sponsors	0	6,337
Deferred Initial Public Offering Costs Incurred but not Yet Paid	0	1,531
Bison Midstream
Cash flows from investing activities:
Acquisition of productive assets	(200,000)	0
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES
Contribution of net assets from SMP Holdings in excess of consideration paid for Bison Midstream	0
Mountaineer Midstream
Cash flows from investing activities:
Acquisition of productive assets	$ (210,000)	$ 0

ORGANIZATION AND BUSINESS OPERATIONS

9 Months Ended

Sep. 30, 2013

Organization, Consolidation and Presentation of Financial Statements [Abstract]

ORGANIZATION AND BUSINESS OPERATIONS

ORGANIZATION, BUSINESS OPERATIONS AND BASIS OF PRESENTATION

Organization. Summit Midstream Partners, LP ("SMLP" or the "Partnership"), a Delaware limited partnership, was formed in May 2012 and began operations in October 2012 in connection with its initial public offering ("IPO") of common limited partner units. SMLP is a growth-oriented limited partnership focused on 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.

Effective with the completion of its IPO on October 3, 2012, SMLP has a 100% ownership interest in Summit Midstream Holdings, LLC ("Summit Holdings") which has a 100% ownership interest in both DFW Midstream Services LLC ("DFW Midstream") and Grand River Gathering, LLC ("Grand River Gathering"). The effects of the IPO and related equity transfers occurring in October 2012 are reflected in SMLP's financial statements. For additional information, see Note 1 to the audited consolidated financial statements included in our annual report on Form 10-K for the year ended December 31, 2012 (the "2012 Annual Report").

On June 4, 2013, Summit Holdings acquired all of the membership interests of Bison Midstream, LLC ("Bison Midstream") from Summit Midstream Partners Holdings, LLC ("SMP Holdings"), a wholly owned direct subsidiary of Summit Midstream Partners, LLC ("Summit Investments") (the "Bison Drop Down"), and thereby acquired certain associated natural gas gathering pipeline, dehydration and compression assets in the Bakken Shale Play in Mountrail and Burke counties in North Dakota (the "Bison Gas Gathering system").

Prior to the Bison Drop Down, on February 15, 2013, Summit Investments acquired Bear Tracker Energy, LLC ("BTE") and subsequently contributed it to SMP Holdings. The Bison Gas Gathering system was carved out from BTE in connection with the Bison Drop Down. As such, it was deemed a transaction among entities under common control. For additional information, see Notes 5, 6 and 12.

On June 21, 2013, Mountaineer Midstream Company, LLC ("Mountaineer Midstream"), a newly formed, wholly owned subsidiary of Summit Holdings, acquired certain natural gas gathering pipeline and compression assets in the Marcellus Shale Play in Doddridge County, West Virginia from an affiliate of MarkWest Energy Partners, L.P. ("MarkWest") (the "Mountaineer Acquisition"). For additional information, see Notes 5, 6 and 12.

Summit Investments is a Delaware limited liability company and the predecessor for accounting purposes (the "Predecessor") of SMLP. Summit Investments was formed and began operations in September 2009. Through August 2011, Summit Investments was wholly owned by Energy Capital Partners II, LLC and its parallel and co-investment funds (collectively, "Energy Capital Partners"). In August 2011, Energy Capital Partners sold an interest in Summit Investments to a subsidiary of GE Energy Financial Services, Inc. ("GE Energy Financial Services", and collectively with Energy Capital Partners, the "Sponsors"). In March 2013, Summit Investments contributed the ownership of its SMLP common and subordinated units along with its 2% general partner interest in SMLP to SMP Holdings in exchange for a continuing 100% interest in SMP Holdings. As of September 30, 2013, SMP Holdings held 14,691,397 SMLP common units, 24,409,850 SMLP subordinated units and 1,091,453 general partner units representing a 2% general partner interest in SMLP.

SMLP is 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, has the right to appoint the entire board of directors of our general partner, including our independent directors. SMLP's operations are conducted through, and our operating assets are owned by, various operating subsidiaries. However, neither SMLP nor its subsidiaries has any employees. The general partner has the sole responsibility for providing the personnel necessary to conduct SMLP's operations, whether through directly hiring employees or by obtaining the services of personnel employed by others, including Summit Investments. All of the personnel that conduct SMLP's business are employed by the general partner and its affiliates, but these individuals are sometimes referred to as our employees.

References to the "Company," "we," or "our," when used for dates or periods ended on or after the IPO, refer collectively to SMLP and its subsidiaries. References to the "Company," "we," or "our," when used for dates or periods ended prior to the IPO, refer collectively to Summit Investments and its subsidiaries.

Business Operations. We provide natural gas gathering and compression services pursuant to long-term, primarily fee-based, natural gas gathering agreements with our customers. Our results are driven primarily by the volumes of natural gas that we gather and compress across our systems. We currently operate in the following unconventional resource basins:


•	the Piceance Basin, which includes the Mesaverde formation and the Mancos and Niobrara shale formations in western Colorado;


•	the Fort Worth Basin, which includes the Barnett Shale formation in north-central Texas;


•	the Williston Basin, which includes the Bakken and Three Forks shale formations in northwestern North Dakota; and


•	the Appalachian Basin, which includes the Marcellus Shale formation in northern West Virginia.

Our operating subsidiaries are Grand River Gathering, DFW Midstream, Bison Midstream and Mountaineer Midstream. All of our operating subsidiaries are midstream energy companies focused on the development, construction and operation of natural gas gathering systems.

Basis of Presentation and Principles of 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. 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.

For the purposes of the unaudited condensed consolidated financial statements, SMLP's results of operations reflect the Partnership's operations subsequent to the IPO and the results of the Predecessor for the period prior to the IPO. The unaudited condensed consolidated financial statements also reflect the results of operations of: (i) Bison Midstream since February 16, 2013 and (ii) Mountaineer Midstream since June 22, 2013. Because the Bison Drop Down was executed between entities under common control, SMLP recognized the acquisition of Bison Midstream at SMP Holdings' historical cost which reflected its fair value accounting for the acquisition of BTE. The excess of SMP Holdings' net investment in Bison Midstream over the purchase price paid by SMLP was recognized as an addition to partners' capital. Due to the common control aspect, the Bison Drop Down was accounted for by the Partnership on an “as if pooled” basis for all periods in which common control existed. See Notes 5, 6 and 12 for additional information. The unaudited condensed consolidated financial statements include the assets, liabilities, and results of operations of SMLP or the Predecessor and their respective wholly owned subsidiaries. All intercompany transactions among the consolidated entities have been eliminated. In our opinion, the accompanying unaudited condensed consolidated financial statements include all adjustments consisting of normal recurring accruals necessary for a fair presentation of the results of operations for the three and nine months ended September 30, 2013 and 2012.

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, although the Partnership believes that the disclosures made are adequate to make the information not misleading. The unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto that are included in our 2012 Annual Report. The results of operations for an interim period are not necessarily indicative of results expected for a full year.

We conduct our operations in the midstream sector with four operating segments. However, due to their similar characteristics and how we manage our business, we have aggregated these segments into one reportable operating segment for disclosure purposes. The assets of our reportable operating segment consist of natural gas gathering systems and related plant and equipment. Our operating segments reflect the way in which we internally report the financial information used to make decisions and allocate resources in connection with our operations.

Reclassifications. Certain reclassifications have been made to prior-year amounts to conform to current-year presentation. These reclassifications had no impact on net income or total partners' capital or membership interests.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

+ References

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+ Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Fair Value of Financial Instruments. The carrying amount of cash and cash equivalents (Level 1), accounts receivable, and accounts payable reported on the balance sheet approximates fair value due to their short-term maturities.

GAAP's fair-value-measurement standard defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three levels of the fair value hierarchy are as follows:


•	Level 1. Inputs represent quoted prices in active markets for identical assets or liabilities;

•

Level 2. Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs); and


•	Level 3. Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement).

Nonfinancial assets and liabilities initially measured at fair value include those acquired and assumed in connection with third-party business combinations.

A summary of the estimated fair value for financial instruments follows.



	September 30, 2013				December 31, 2012
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Revolving credit facility	$	265,050	$	265,050	$	199,230	$	199,230
Senior notes	300,000		308,500		—		—

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 September 30, 2013. The use of different market assumptions or valuation methodologies may have a material effect on the estimated fair value of the senior notes.

Intangible Assets and Noncurrent Liability. Upon the acquisition of DFW Midstream, certain of our gas gathering contracts were deemed to have above-market pricing structures while another was deemed to have pricing that was below market. We have recognized the contracts that were above market at acquisition as favorable gas gathering contracts. We have recognized the contract that was deemed to be below market as a noncurrent liability. We amortize these intangibles on a units-of-production basis over the estimated useful life of the contract. We define useful life as the period over which the contract is expected to contribute directly or indirectly to our future cash flows. The related contracts have original terms ranging from 10 years to 20 years. We recognize the amortization expense associated with these intangible assets and liabilities in revenue.

For our other gas gathering contracts, we amortize contract intangible assets over the period of economic benefit based upon the expected revenues over the life of the contract. The useful life of these contracts ranges from 10 years to 25 years. We recognize the amortization expense associated with these intangible assets in depreciation and amortization expense.

We have right-of-way intangible assets associated with city easements and easements granted within existing rights-of-way. We amortize these intangible assets over the shorter of the contractual term of the rights-of-way or the estimated useful life of the gathering system. The contractual terms of the rights-of-way range from 20 years to 30 years. The estimated useful life of our gathering systems is 30 years. We recognize the amortization expense associated with these intangible assets in depreciation and amortization expense.

Other Noncurrent Assets. Other noncurrent assets primarily consist of external costs incurred in connection with the issuance of our senior notes and the closing of our revolving credit facility and related amendments. We capitalize and then amortize these deferred loan costs over the life of the respective debt instrument. We recognize amortization of deferred loan costs in interest expense.

Revenue Recognition. We generate the majority of our revenue from the natural gas gathering services that we provide to our natural gas producer customers. We also generate revenue from our marketing of natural gas and natural gas liquids ("NGLs"). We realize revenues by receiving fees from our producer customers or by selling the residue natural gas and NGLs.

We recognize revenue earned from gathering services in gathering services and other fees revenue. We also earn revenue from the sale of physical natural gas purchased from our customers under percentage-of-proceeds arrangements. These revenues are recognized in natural gas, NGLs and condensate sales and other with corresponding expense recognition in cost of natural gas and NGLs. We sell the natural gas that we retain from our DFW Midstream customers to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate retained from our gathering services at Grand River Gathering. Revenues from the retainage of natural gas and condensate are recognized in natural gas, NGLs and condensate sales and other; the associated expense is included in operation and maintenance expense.

We recognize revenue when all of the following criteria are met: (i) persuasive evidence of an exchange arrangement exists, (ii) delivery has occurred or services have been rendered, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured.

We obtain access to natural gas and provide services principally under contracts that contain one or both of the following arrangements:

•

Fee-based arrangements. Under fee-based arrangements, we receive a fee or fees for one or more of the following services: natural gas gathering, compressing, and treating. Fee-based arrangements include natural gas purchase arrangements pursuant to which we purchase natural gas at the wellhead, or other receipt points, at a settled price at the delivery point less a specified amount, generally the same as the fees we would otherwise charge for gathering of natural gas from the wellhead location to the delivery point. The margins earned are directly related to the volume of natural gas that flows through the system.

•

Percent-of-proceeds arrangements. Under percent-of-proceeds arrangements, we generally purchase natural gas from producers at the wellhead, or other receipt points, gather the wellhead natural gas through our gathering system, treat the natural gas, and sell the natural gas to a third party for processing. We then remit to our producers an agreed-upon percentage of the actual proceeds received from sales of the residue natural gas and NGLs. Certain of these arrangements may also result in returning all or a portion of the residue natural gas and/or the NGLs to the producer, in lieu of returning sales proceeds.

Many of our natural gas gathering agreements provide for a monthly or annual minimum volume commitment ("MVC") from certain of our customers. Under these monthly or annual MVCs, our customers agree to ship a minimum volume of natural gas on our gathering systems or to pay a minimum monetary amount over certain periods during the term of the MVC. A customer must make a shortfall payment to us at the end of the contract month or year, as applicable, if its actual throughput volumes are less than its MVC for that month or year. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent periods to the extent that such customer's throughput volumes in subsequent periods exceed its MVC for that period. These contract provisions range from 12 months to eight years.

We record customer billings for obligations under their MVCs as deferred revenue when the customer has the right to utilize shortfall payments to offset gathering fees in subsequent periods. We recognize deferred revenue under these arrangements in revenue once all contingencies or potential performance obligations associated with the related volumes have either (i) been satisfied through the gathering of future excess volumes of natural gas, or (ii) expired (or lapsed) through the passage of time pursuant to the terms of the applicable natural gas gathering agreement. We classify deferred revenue as short term for arrangements where the expiration of a customer's right to utilize shortfall payments is twelve months or less. As of September 30, 2013, we have billed $24.1 million of deferred revenue relative to shortfall payments, of which $1.1 million was included in accounts receivable, attributable to arrangements that provide the customer the ability to offset gathering fees in the next one month to eight years to the extent that a customer's throughput volumes exceed its MVC.

Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis.

Unit-Based Compensation. For awards of unit-based compensation, we determine a grant date fair value and recognize the related compensation expense, adjusted for expected forfeitures, in the statement of operations over the vesting period of the respective awards. See Note 8 for additional information.

Income Taxes. We are not subject to federal and state income taxes, except as noted below, because we are structured as a partnership. As a result, our unitholders or members are individually responsible for paying federal and state income taxes on their share of our taxable income.

In general, legal entities that are chartered, organized or conducting business in the state of Texas are subject to the Revised Texas Franchise Tax (the "Texas Margin Tax"). The Texas Margin Tax has the characteristics of an income tax because it is determined by applying a tax rate to a tax base that considers both revenues and expenses. Our financial statements reflect provisions for these tax obligations.

Earnings Per Unit ("EPU"). We present earnings per limited partner unit data only for periods subsequent to the closing of SMLP’s IPO in October 2012. EPU for periods ended prior to the IPO have not been presented because Summit Investments' members held membership interests and not units.

We determine EPU by dividing the net income that is attributed, in accordance with the net income and loss allocation provisions of the partnership agreement, to the common and subordinated unitholders under the two-class method, after deducting the general partner's 2% interest in net income and any incentive distributions paid to the general partner, by the weighted-average number of common and subordinated units outstanding during the three and nine months ended September 30, 2013. Diluted earnings per limited partner unit reflects the potential dilution that could occur if securities or other agreements to issue common units, such as unit-based compensation, were exercised, settled or converted into common units. When it is determined that potential common units resulting from an award subject to performance or market conditions should be included in the diluted earnings per limited partner unit calculation, the impact is reflected by applying the treasury stock method.

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. Although we believe that we are in material compliance with applicable environmental regulations, the risk of costs and liabilities are inherent in pipeline ownership and operation. 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. There are no such liabilities reflected in the accompanying financial statements at September 30, 2013 or December 31, 2012. However, we can provide no assurances that significant costs and liabilities will not be incurred by the Partnership in the future. We are currently not aware of any material contingent liabilities that exist with respect to environmental matters.

Other Significant Accounting Policies. For information on our other significant accounting policies, see Note 2 of the audited consolidated financial statements included in the 2012 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 will materially affect our financial statements.

PROPERTY, PLANT, AND EQUIPMENT, NET

9 Months Ended

Sep. 30, 2013

Property, Plant and Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT, NET

Details on property, plant, and equipment, net were as follows:



	Useful lives (In years)	September 30,			December 31,
	Useful lives (In years)	2013			2012
	(Dollars in thousands)
Gas gathering systems	30	$	618,528		$	427,449
Compressor stations and compression equipment	30	334,108			237,618
Construction in progress	n/a	50,381			45,919
Other	4-15	9,680			4,524
Total		1,012,697			715,510
Accumulated depreciation		(55,142		)	(33,517		)
Property, plant, and equipment, net		$	957,555		$	681,993

The increase in property, plant, and equipment primarily reflects the recognition of gas gathering system fixed assets acquired in connection with the Bison Drop Down and Mountaineer Acquisition.

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



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Depreciation expense	$	8,429	$	5,623	$	21,625	$	15,682
Capitalized interest	1,838		310		2,808		2,191

IDENTIFIABLE INTANGIBLE ASSETS AND NONCURRENT LIABILITY

9 Months Ended

Sep. 30, 2013

Goodwill and Intangible Assets Disclosure [Abstract]

IDENTIFIABLE INTANGIBLE ASSETS AND NONCURRENT LIABILITY

IDENTIFIABLE INTANGIBLE ASSETS, NONCURRENT LIABILITY AND GOODWILL

Identifiable Intangible Assets and Noncurrent Liability. Identifiable intangible assets and the noncurrent liability, which are subject to amortization, were as follows:



	September 30, 2013
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(5,847	)	$	18,348
Contract intangibles	16.8	429,575		(34,771		)	394,804
Rights-of-way	28.3	55,773		(4,116		)	51,657
Total amortizable intangible assets		$	509,543	$	(44,734	)	$	464,809

Unfavorable gas gathering contract	10.0	$	10,962	$	(4,358	)	$	6,604



	December 31, 2012
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(4,237	)	$	19,958
Contract intangibles	12.4	244,100		(14,504		)	229,596
Rights-of-way	28.3	38,848		(2,862		)	35,986
Total amortizable intangible assets		$	307,143	$	(21,603	)	$	285,540

Unfavorable gas gathering contract	10.0	$	10,962	$	(3,542	)	$	7,420

The increase in total amortizable intangible assets primarily reflects the recognition of gas gathering contracts and rights-of-way acquired in connection with the Bison Drop Down and the Mountaineer Acquisition.

We recognized amortization expense as follows:



	Three months ended September 30,						Nine months ended September 30,
	2013			2012			2013			2012
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	511		$	501		$	1,610		$	1,181
Amortization expense – contract intangibles	7,559			3,194			20,267			9,483
Amortization expense – rights-of-way	438			340			1,254			970
Amortization expense – unfavorable gas gathering contract	(247		)	(341		)	(816		)	(1,206		)

The estimated aggregate annual amortization of intangible assets and noncurrent liability expected to be recognized as of September 30, 2013 for the remainder of 2013 and each of the four succeeding fiscal years follows.



	Assets		Liabilities
	(In thousands)
2013	$	8,801	$	378
2014	36,949		1,549
2015	39,628		1,650
2016	39,754		1,571
2017	38,316		1,456

Goodwill. We recognized goodwill of $45.5 million in connection with the acquisition of Grand River Gathering in 2011 and allocated it to the Grand River Gathering reporting unit. We recognized goodwill of $54.2 million in connection with the Bison Drop Down in June 2013 and allocated it to the Bison Midstream reporting unit. The goodwill attributed to Bison Midstream represents its allocation of the goodwill that Summit Investments recognized in connection with its acquisition of BTE assets in February 2013. We preliminarily recognized goodwill of $18.1 million in connection with the Mountaineer Acquisition in June 2013 and allocated it to the Mountaineer Midstream reporting unit. Goodwill allocated to the Mountaineer Midstream reporting unit will be finalized in conjunction with the finalization of the acquisition accounting. See Notes 1 and 12 for additional information. A rollforward of the consolidated balance of goodwill for the nine months ended September 30, 2013 follows.



	(In thousands)
Goodwill, beginning of period	$	45,478
Goodwill recognized in connection with the Bison Drop Down	54,199
Goodwill preliminarily recognized in connection with the Mountaineer Acquisition	18,089
Goodwill, end of period	$	117,766

We evaluate goodwill for impairment annually on September 30. We also evaluate goodwill whenever events or circumstances indicate that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. We performed our annual goodwill impairment testing as of September 30, 2013 using a combination of the income and market approaches and determined that the fair value of each of the reporting units exceeded their carrying value resulting in no goodwill impairment. There have been no impairments of goodwill.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

LONG-TERM DEBT

9 Months Ended

Sep. 30, 2013

REVOLVING CREDIT FACILITY [Abstract]

REVOLVING CREDIT FACILITY

LONG-TERM DEBT

Long-term debt consisted of the following:



	September 30,		December 31,
	2013		2012
	(In thousands)
Variable rate senior secured revolving credit facility (3.43% at September 30, 2013 and 2.98% at December 31, 2012) due November 2018	$	265,050	$	199,230
7.50% Senior unsecured notes due July 2021	300,000		—
Total long-term debt	$	565,050	$	199,230

Revolving Credit Facility. We have a senior secured revolving credit facility. In June 2013, we exercised the revolving credit facility's $50.0 million accordion provision and increased the total commitments thereunder from $550.0 million to $600.0 million. We also borrowed $200.0 million in connection with the Bison Drop Down and $110.0 million in connection with the Mountaineer Acquisition. See Notes 1, 6 and 12 for additional information. Also in June 2013, we used the proceeds from our senior notes offering to repay $294.2 million of our revolving credit facility. As of September 30, 2013, the outstanding balance of the revolving credit facility was $265.1 million.

The revolving credit facility is secured by the membership interests of Summit Holdings, DFW Midstream, Grand River Gathering, Bison Midstream and Mountaineer Midstream and substantially all of the assets of these entities. It is guaranteed by SMLP and all of its subsidiaries, except for Summit Midstream Finance Corp. ("Finance Corp.") and allows for revolving loans, letters of credit and swingline loans.

Borrowings under the revolving credit facility bear interest at the London Interbank Offered Rate ("LIBOR") plus an applicable margin or a base rate, as defined in the credit agreement. At September 30, 2013, the applicable margin under LIBOR borrowings was 3.25%, the interest rate was 3.43% and the unused portion of the revolving credit facility totaled $334.9 million (subject to a commitment fee of 0.50%).

The revolving credit agreement contains affirmative and negative covenants customary for credit facilities of its size and nature that, among other things, limit or restrict the ability to: (i) incur additional debt; (ii) make investments; (iii) engage in certain mergers, consolidations, acquisitions or sales of assets; (iv) enter into swap agreements and power purchase agreements; (v) enter into leases that would cumulatively obligate payments in excess of $30.0 million over any 12-month period; and (vi) prohibits the payment of distributions by Summit Holdings if a default then exists or would result therefrom, and otherwise limits the amount of distributions Summit Holdings can make. In addition, the revolving credit facility requires Summit Holdings to maintain a ratio of consolidated trailing 12-month earnings before interest, income taxes, depreciation and amortization ("EBITDA") to net interest expense of not less than 2.5 to 1.0 (as defined in the credit agreement) and a ratio of total net indebtedness to consolidated trailing 12-month EBITDA of not more than 5.0 to 1.0, or not more than 5.5 to 1.0 for up to six months following certain acquisitions (as defined in the credit agreement).

As of September 30, 2013, we were in compliance with the covenants in the revolving credit facility. There were no defaults or events of default during the nine months ended September 30, 2013.

In November 2013, we closed on an amendment and restatement of the revolving credit facility which: (i) increases the borrowing capacity to $700.0 million, (ii) extends the maturity to November 2018, (iii) includes a $200.0 million accordion feature, (iv) reduces the leverage-based pricing grid by 0.75% to a new range of 1.75% to 2.75%, (v) changes the commitment fee to a leverage-based range of 0.30% to 0.50%, and (vi) adds Finance Corp. as a subsidiary guarantor.

Senior Notes. On June 17, 2013, Summit Holdings and its 100% owned finance subsidiary, Finance Corp. (together with Summit Holdings, the "Co-Issuers"), issued $300.0 million of 7.50% senior unsecured notes maturing July 1, 2021 (the "senior notes"). The senior notes were sold within the United States only to qualified institutional buyers in reliance on Rule 144A under the Securities Act of 1933, as amended (the "Securities Act"), and outside the United States only to non-U.S. persons in reliance on Regulation S under the Securities Act. The senior notes have not been registered under the Securities Act or any state securities laws, and, unless so registered, may not be offered or sold in the United States except pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and applicable state securities laws.

We will pay interest on the senior notes semi-annually in cash in arrears on January 1 and July 1 of each year, commencing January 1, 2014. The senior notes are senior, unsecured obligations and rank equally in right of payment with all of our existing and future senior obligations. The senior notes are effectively subordinated in right of payment to all of our secured indebtedness, to the extent of the collateral securing such indebtedness. We used the proceeds from the issuance of the senior notes to repay a portion of the balance outstanding under our revolving credit facility. Debt issuance costs of $7.3 million, recognized in other noncurrent assets, are being amortized over the life of the 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 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 and the 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 senior notes. There are no significant restrictions on the ability of SMLP or Summit Holdings to obtain funds from its subsidiaries by dividend or loan.

Under a registration rights agreement, the Co-Issuers and the Guarantors have agreed to file a registration statement with the SEC pursuant to which the Co-Issuers will either offer to exchange the senior notes and the guarantees for registered notes and guarantees with substantially identical terms or, in certain circumstances, register the resale of the senior notes and their guarantees (the "Exchange Offer").

If the Exchange Offer is not completed (or, if required, the shelf registration statement is not declared effective or does not automatically become effective) on or before the 365th day following the date of issuance of the senior notes (the ‘‘Exchange Completion Deadline’’), the Co-Issuers will be required to pay additional interest in an amount equal to 0.25% per annum of the principal amount of senior notes with respect to the first 90-day period following the Exchange Completion Deadline. The amount of the additional interest will increase by an additional 0.25% per annum with respect to each subsequent 90-day period, up to a maximum amount of additional interest of 1.0% per annum of the principal amount of senior notes outstanding until the Exchange Offer is completed or the shelf registration statement is declared effective (or becomes automatically effective). All accrued additional interest will be paid by the Co-Issuers and the Guarantors on the next scheduled interest payment date in the same manner as other interest is paid on the senior notes. Following the time that the senior notes are registered, the accrual of additional interest will cease.

At any time prior to July 1, 2016, the Co-Issuers may redeem up to 35% of the aggregate principal amount of the senior notes at a redemption price of 107.500% of the principal amount of the senior notes, plus accrued and unpaid interest, if any, to the redemption date, with an amount not greater than the net cash proceeds of certain equity offerings. On and after July 1, 2016, the Co-Issuers may redeem all or part of the senior notes at a redemption price of 105.625% (with the redemption premium declining ratably each year to 100.000% on July 1, 2019), plus accrued and unpaid interest, if any.

The indenture restricts SMLP’s and the Co-Issuers’ ability and the ability of certain of their subsidiaries to: (i) incur additional debt or issue preferred stock; (ii) make distributions, repurchase equity or redeem subordinated debt; (iii) make payments on subordinated indebtedness; (iv) create liens or other encumbrances; (v) make investments, loans or other guarantees; (vi) sell or otherwise dispose of a portion of their assets; (vii) engage in transactions with affiliates; and (viii) make acquisitions or merge or consolidate with another entity. These covenants are subject to a number of important exceptions and qualifications. At any time when the senior notes are rated investment grade by each of Moody’s Investors Service, Inc. and Standard & Poor’s Ratings Services and no default or event of default under the indenture has occurred and is continuing, many of these covenants will terminate.

The indenture provides that each of the following is an event of default: (i) default for 30 days in the payment when due of interest on the senior notes; (ii) default in the payment when due of the principal of, or premium, if any, on the senior notes; (iii) failure by the Co-Issuers or SMLP to comply with certain covenants relating to merger, consolidation, sale of assets, change of control or asset sales; (iv) failure by SMLP for 180 days after notice to comply with certain covenants relating to the filing of reports with the SEC; (v) failure by the Co-Issuers or SMLP for 30 days after notice to comply with any of the other agreements in the indenture; (vi) specified defaults under any mortgage, indenture or instrument under which there may be issued or by which there may be secured or evidenced any indebtedness for money borrowed by SMLP or any of its restricted subsidiaries (or the payment of which is guaranteed by SMLP or any of its restricted subsidiaries); (vii) failure by SMLP or any of its restricted subsidiaries to pay certain final judgments aggregating in excess of $20.0 million; (viii) except as permitted by the indenture, any guarantee of the senior notes shall cease for any reason to be in full force and effect or any guarantor, or any person acting on behalf of any guarantor, shall deny or disaffirm its obligations under its guarantee of the senior notes; and (ix) certain events of bankruptcy, insolvency or reorganization described in the indenture. In the case of an event of default as described in the foregoing clause (ix), all outstanding senior notes will become due and payable immediately without further action or notice. If any other event of default occurs and is continuing, the trustee or the holders of at least 25% in principal amount of the then outstanding senior notes may declare all the senior notes to be due and payable immediately.

There were no defaults or events of default during the period from issuance through September 30, 2013.

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS

9 Months Ended

Sep. 30, 2013

Equity [Abstract]

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS

Partners' Capital

SMLP was formed in May 2012. Prior to the closing of its IPO on October 3, 2012, SMLP had no outstanding common or subordinated units or operations. A rollforward of the number of common limited partner, subordinated limited partner and general partner units from December 31, 2012 to September 30, 2013 follows.



	Common	Subordinated	General partner	Total
Units, beginning of period	24,412,427	24,409,850	996,320	49,818,597
Units issued to SMP Holdings in connection with the Bison Drop Down	1,553,849	—	31,711	1,585,560
Units issued to SMP Holdings in connection with the Mountaineer Acquisition	3,107,698	—	63,422	3,171,120
Units issued	1,473	—	—	1,473
Units, end of period	29,075,447	24,409,850	1,091,453	54,576,750

Bison Drop Down. On June 4, 2013, SMLP acquired Bison Midstream from SMP Holdings. SMP Holdings contributed 100% of the membership interests in Bison Midstream to SMLP, which concurrently contributed the membership interests to Summit Holdings. In exchange for its $305.4 million net investment in Bison Midstream, SMLP paid SMP Holdings and the general partner total cash and unit consideration of $248.9 million. As a result of the contribution of net assets in excess of consideration, SMLP recognized a capital contribution from SMP Holdings. The details of total cash and unit consideration as well as the calculation of the capital contribution and its allocation to partners' capital follow.



	(Dollars in thousands)
SMP Holdings' net investment in Bison Midstream			$	305,449
Aggregate cash paid to SMP Holdings	$	200,000
Issuance of 1,553,849 SMLP common units to SMP Holdings	47,936
Issuance of 31,711 SMLP general partner units to the general partner	978
Total consideration			248,914
SMP Holdings' contribution of net assets in excess of consideration			$	56,535

Allocation of capital contribution:
General partner interest	$	1,131
Common limited partner interest	28,558
Subordinated limited partner interest	26,846
Partners' capital allocation			$	56,535

The number of units issued to SMP Holdings and the general partner in connection with the Bison Drop Down was calculated based on an assumed equity issuance of $50.0 million and the five-day volume-weighted-average price as of June 3, 2013 of $31.53 per unit. The units were then valued as of June 4, 2013 (the date of closing) using the June 4, 2013 closing price of SMLP's units of $30.85.

The general partner interest allocation was calculated based on a 2% general partner interest in the contribution of assets in excess of consideration given by SMLP to SMP Holdings. Common and subordinated limited partner interests allocations were calculated as their respective percentages of total limited partner capital applied to the balance of the contribution by SMP Holdings after giving effect to the general partner allocation. See Notes 1, 5 and 12 for additional information.

Mountaineer Acquisition. On June 4, 2013, SMLP executed definitive agreements with MarkWest to acquire the Mountaineer Midstream system. On June 21, 2013, prior to closing the Mountaineer Acquisition and in accordance with the definitive agreements with MarkWest (the "MarkWest Agreement"), Mountaineer Midstream acquired all of the Mountaineer Gathering system assets. The total acquisition purchase price of $210.0 million was funded with $110.0 million of borrowings under SMLP’s revolving credit facility and the issuance of $100.0 million of SMLP common units and general partner interests to SMP Holdings and the general partner for cash. The allocation and valuation of units issued to SMP Holdings and the general partner to partially fund the Mountaineer Acquisition follow.



	(Dollars in thousands)
Issuance of 3,107,698 SMLP common units to SMP Holdings	$	98,000
Issuance of 63,422 SMLP general partner units to the general partner	2,000
Issuance of units in connection with the Mountaineer Acquisition	$	100,000

Pursuant to a unit purchase agreement, the number of units issued to SMP Holdings and the general partner in connection with the Mountaineer Acquisition was calculated based on an assumed equity issuance of $100.0 million and the five-day volume-weighted-average price as of June 3, 2013 of $31.53 per unit. See Notes 1, 5 and 12 for additional information.

Subordination. The principal difference between our common units and subordinated units is that in any quarter during the subordination period, holders of the subordinated units are not entitled to receive any distribution of available cash until the common units have received the minimum quarterly distribution plus any arrearages in the payment of the minimum quarterly distribution from prior quarters. Subordinated units will not accrue arrearages for unpaid quarterly distributions or quarterly distributions less than the minimum quarterly distribution. If we do not pay the minimum quarterly distribution on our common units, our common unitholders will not be entitled to receive such payments in the future except during the subordination period. To the extent we have available cash in any future quarter during the subordination period in excess of the amount necessary to pay the minimum quarterly distribution to holders of our common units, we will use this excess available cash to pay any distribution arrearages related to prior quarters before any cash distribution is made to holders of subordinated units. When the subordination period ends, all subordinated units will convert into common units on a one-for-one basis, and thereafter no common units will be entitled to arrearages.

The subordination period will end on the first business day after we have earned and paid at least (1) $1.60 (the minimum quarterly distribution on an annualized basis) on each outstanding common unit and subordinated unit and the corresponding distribution on the general partner's 2.0% interest for each of three consecutive, non-overlapping four-quarter periods ending on or after December 31, 2015 or (2) $2.40 (150.0% of the annualized minimum quarterly distribution) on each outstanding common unit and subordinated unit and the corresponding distributions on the general partner's 2.0% interest and the related distribution on the incentive distribution rights for the four-quarter period immediately preceding that date, in each case provided there are no arrearages on the common units at that time.

Cash Distribution Policy

Our partnership agreement requires that we distribute all of our available cash (as defined below) within 45 days after the end of each quarter to unitholders of record on the applicable record date. Our policy is to distribute to our unitholders an amount of cash each quarter that is equal to or greater than the minimum quarterly distribution stated in our partnership agreement.

Details of cash distributions declared during 2013 follow.



Attributable to the quarter ended	Payment date	Per-unit distribution		Cash paid (or payable) to common unitholders		Cash paid (or payable) to subordinated unitholders		Cash paid (or payable) to general partner		Total distribution
		(Dollars in thousands, except per-unit amounts)
December 31, 2012	February 14, 2013	$	0.4100	$	10,009	$	10,008	$	408	$	20,425
March 31, 2013	May 15, 2013	0.4200		10,253		10,252		418		20,923
June 30, 2013	August 14, 2013	0.4350		12,647		10,618		475		23,740
September 30, 2013	November 14, 2013	0.4600		13,377		11,229		502		25,108

Minimum Quarterly Distribution. Our partnership agreement generally requires that we make a minimum quarterly distribution to the holders of our common units and subordinated units of $0.40 per unit, or $1.60 on an annualized basis, to the extent we have sufficient cash from our operations after the establishment of cash reserves and the payment of costs and expenses, including reimbursements of expenses to our general partner. The amount of distributions paid under our policy and the decision to make any distribution is determined by our general partner, taking into consideration the terms of our partnership agreement.

Definition of Available Cash. Available cash generally means, for any quarter, all cash on hand at the end of that quarter:


•	less the amount of cash reserves established by our general partner at the date of determination of available cash for that quarter to:


•	provide for the proper conduct of our business (including reserves for our future capital expenditures and anticipated future debt service requirements);


•	comply with applicable law, any of our debt instruments or other agreements; or

•

provide funds for distributions to our unitholders and to our general partner for any one or more of the next four quarters (provided that our general partner may not establish cash reserves for distributions unless it determines that the establishment of reserves will not prevent us from distributing the minimum quarterly distribution on all common units and any cumulative arrearages on such common units for the current quarter);


•	plus, if our general partner so determines, all or any portion of the cash on hand on the date of determination of available cash for the quarter resulting from working capital borrowings made subsequent to the end of such quarter.

General Partner Interest and Incentive Distribution Rights. Our general partner is entitled to 2.0% of all distributions that we make prior to our liquidation. Our general partner has the right, but not the obligation, to contribute a proportionate amount of capital to us to maintain its current general partner interest. Our general partner's initial 2.0% interest in our distributions will be reduced if we issue additional units in the future and our general partner does not contribute a proportionate amount of capital to us to maintain its 2.0% general partner interest.

Our general partner also currently holds incentive distribution rights that entitle it to receive increasing percentage allocations, up to a maximum of 50.0% (as set forth in the chart below), of the cash we distribute from operating surplus in excess of $0.46 per unit per quarter. The maximum distribution of 50.0% includes distributions paid to our general partner on its 2.0% general partner interest and assumes that our general partner maintains its general partner interest at 2.0%. The maximum distribution of 50.0% does not include any distributions that our general partner may receive on any common or subordinated units that it owns.

Percentage Allocations of Available Cash. The following table illustrates the percentage allocations of available cash between the unitholders and our general partner based on the specified target distribution levels. The amounts set forth in the column Marginal Percentage Interest in Distributions are the percentage interests of our general partner and the unitholders in any available cash we distribute up to and including the corresponding amount in the column Total Quarterly Distribution Per Unit Target Amount. The percentage interests shown for our unitholders and our general partner for the minimum quarterly distribution are also applicable to quarterly distribution amounts that are less than the minimum quarterly distribution. The percentage interests set forth below for our general partner include its 2.0% general partner interest and assume that our general partner has contributed any additional capital necessary to maintain its 2.0% general partner interest, our general partner has not transferred its incentive distribution rights and that there are no arrearages on common units.



	Total quarterly distribution per unit target amount	Marginal percentage interest in distributions
	Total quarterly distribution per unit target amount	Unitholders	General partner
Minimum quarterly distribution	$0.40	98.0%	2.0%
First target distribution	$0.40 up to $0.46	98.0%	2.0%
Second target distribution	above $0.46 up to $0.50	85.0%	15.0%
Third target distribution	above $0.50 up to $0.60	75.0%	25.0%
Thereafter	above $0.60	50.0%	50.0%

Membership Interests

Energy Capital Partners and GE Energy Financial Services hold membership interests in Summit Investments. Such membership interests give them the right to participate in distributions and to exercise the other rights or privileges available to each entity under Summit Investments' Amended and Restated Limited Liability Operating Agreement (the "Summit LLC Agreement"). In addition, certain members of Summit Investments’ management hold ownership interests in the form of Class B membership interests (the "SMP Net Profits Interests") through their ownership in Summit Midstream Management, LLC.

In accordance with the Summit LLC Agreement, capital accounts are maintained for Summit Investments’ members. The capital account provisions of the Summit LLC Agreement incorporate principles established for U.S. federal income tax purposes and as such are not comparable to the equity accounts reflected under GAAP in our consolidated financial statements.

The Summit LLC Agreement sets forth the calculation to be used in determining the amount and priority of cash distributions that its membership interest holders will receive. Capital contributions required under the Summit LLC Agreement are in proportion to the members' respective percentage ownership interests. The Summit LLC Agreement also contains provisions for the allocation of net earnings and losses to members. For purposes of maintaining partner capital accounts, the Summit LLC Agreement specifies that items of income and loss shall be allocated among the partners in accordance with their respective percentage interests.

In April 2013, we repurchased the outstanding net profits interests in DFW Midstream. See Note 8 for additional information.

EARNINGS PER UNIT

9 Months Ended

Sep. 30, 2013

Earnings Per Share [Abstract]

EARNINGS PER UNIT

The following table presents details on EPU.



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(Dollars in thousands, except per-unit amounts)
Net income	$	6,691	$	27,291
Less: net income attributable to SMP Holdings	—		52
Net income attributable to partners	6,691		27,239
Less: net income attributable to general partner	134		545
Net income attributable to limited partners	$	6,557	$	26,694

Net income attributable to common units	$	3,567	$	14,899

Weighted-average common units outstanding – basic	29,074,743		26,234,042
Earnings per common unit – basic	$	0.12	$	0.57

Weighted-average common units outstanding – diluted	29,227,041		26,352,234
Earnings per common unit – diluted	$	0.12	$	0.57

Net income attributable to subordinated units	$	2,990	$	11,795

Weighted-average subordinated units outstanding – basic and diluted	24,409,850		24,409,850
Earnings per subordinated unit – basic and diluted	$	0.12	$	0.48

The effect of nonvested phantom units and nonvested restricted units on the weighted-average number of units used to calculate diluted earnings per common limited partner unit was 152,298 units for the three months ended September 30, 2013 and 118,192 units for the nine months ended September 30, 2013. There were no units excluded from diluted earnings per unit as we do not have any anti-dilutive units for the three and nine months ended September 30, 2013. See Note 8 for additional information.

UNIT-BASED COMPENSATION

9 Months Ended

Sep. 30, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

UNIT-BASED COMPENSATION

Long-Term Incentive Plan. The Long-Term Incentive Plan (the "LTIP") provides for equity awards to eligible officers, employees, consultants and directors of our general partner and its affiliates, thereby linking the recipients' compensation directly to SMLP’s performance. The LTIP is administered by our general partner's board of directors, though such administration function may be delegated to a committee appointed by the board. A total of 5.0 million common units was reserved for issuance pursuant to and in accordance with the LTIP. As of September 30, 2013, approximately 4.7 million common units remained available for future issuance.

The LTIP provides for the granting, from time to time, of unit-based awards, including common units, restricted units, phantom units, unit options, unit appreciation rights, distribution equivalent rights, profits interest units and other unit-based awards. Grants are made at the discretion of the board of directors or compensation committee of our general partner. The administrator of the LTIP may make grants under the LTIP that contain such terms, consistent with the LTIP, as the administrator may determine are appropriate, including vesting conditions. The administrator of the LTIP may, in its discretion, base vesting on the grantee's completion of a period of service or upon the achievement of specified financial objectives or other criteria or upon a change of control (as defined in the LTIP) or as otherwise described in an award agreement. Termination of employment prior to vesting will result in forfeiture of the awards, except in limited circumstances as described in the plan documents. Units that are canceled or forfeited will be available for delivery pursuant to other awards.

The following table presents phantom and restricted unit activity:



	Units		Weighted-average grant date fair value
Nonvested phantom and restricted units, January 1, 2013	131,558		$	20.00
Phantom units granted	155,330		$	26.33
Restricted units granted	835		$	27.50
Phantom units forfeited	(4,041	)	$	25.99
Nonvested phantom and restricted units, September 30, 2013	283,682		$	23.41

A phantom unit is a notional unit that entitles the grantee to receive a common unit upon the vesting of the phantom unit or on a deferred basis upon specified future dates or events or, in the discretion of the administrator, cash equal to the fair market value of a common unit. Distribution equivalent rights for each phantom unit provide for a lump sum cash amount equal to the accrued distributions from the grant date to be paid in cash upon the vesting date. The phantom units granted in 2013 vest ratably over a three-year period. Upon vesting, awards may be settled in cash and/or common units, at the discretion of the board of directors.

Upon vesting, management intends to settle all phantom unit awards with common units. As of September 30, 2013, the unrecognized unit-based compensation related to the LTIP was $4.4 million. Incremental unit-based compensation will be recorded over the remaining vesting period of 2.92 years. Due to the limited and immaterial forfeiture history associated with the grants under the LTIP, no forfeitures were assumed in the determination of estimated compensation expense.

Unit-based compensation recognized in general and administrative expense related to awards under the LTIP was as follows:



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(In thousands)
SMLP unit-based compensation	$	829	$	1,970

DFW Net Profits Interests. Class B membership interests in DFW Midstream (the "DFW Net Profits Interests") participated in distributions upon time vesting and the achievement of certain distribution targets to Class A members or higher priority vested DFW Net Profits Interests. The DFW Net Profits Interests were accounted for as compensatory awards. All grants vested ratably and provided for accelerated vesting in certain limited circumstances, including a qualifying termination following a change in control (as defined in the underlying award agreement and the DFW Midstream Amended and Restated Limited Liability Company Agreement and Contribution Agreement).

We recognized unit-based compensation ratably over the respective award's vesting period. Unit-based compensation recognized in general and administrative expense related to the DFW Net Profits Interests was as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Class B membership interest unit-based compensation	$	—	$	75	$	17	$	874

Beginning in October 2012 and continuing into April 2013, we entered into a series of repurchases with the remaining seven holders of the then-outstanding DFW Net Profits Interests whereby we exchanged $12.2 million for their vested DFW Net Profits Interests and 7,393 SMLP restricted units for their unvested DFW Net Profits Interests. The repurchase prices were determined by valuing the vested and unvested net profits interests in relation to the enterprise value of DFW Midstream and represented fair value at the dates of repurchase. Upon the conclusion of these repurchase transactions, there were no remaining or outstanding DFW Net Profits Interests as of April 30, 2013.

CONCENTRATIONS OF RISK

9 Months Ended

Sep. 30, 2013

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, at times, may 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 are primarily from natural gas producers shipping natural gas. 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 generally require letters of credit for receivables from counterparties that are judged to have sub-standard credit, unless the credit risk can otherwise be mitigated.

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



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
Revenue:
Counterparty A	17	%	29	%	19	%	19	%
Counterparty B	16	%	29	%	18	%	27	%
Counterparty C	10	%	—	%	9	%	—	%
Counterparty D	10	%	—	%	9	%	—	%
Counterparty E	*		13	%	*		14	%

__________

* Less than 10%

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



	September 30,		December 31,
	2013		2012
Accounts receivable:
Counterparty A	23	%	24	%
Counterparty B	21	%	38	%
Counterparty C	*		—	%
Counterparty D	*		—	%
Counterparty E	*		*

__________

* Less than 10%

RELATED-PARTY TRANSACTIONS

9 Months Ended

Sep. 30, 2013

RELATED-PARTY TRANSACTIONS

Recent Acquisitions and Partners' Capital Issuances. See Notes 5, 6 and 12 for disclosure of the purchase of Bison Midstream from SMP Holdings and the issuance of common units and general partner interests to SMP Holdings in connection with the Bison Drop Down and the Mountaineer Acquisition.

General and Administrative Expense Allocation. 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. In addition, we reimburse our general partner for compensation, travel and entertainment expenses for the directors serving on the board of directors of our general partner and the cost of director and officer liability insurance. Our partnership agreement provides that our general partner will determine in good faith the expenses that are allocable to us.

The payable to our general partner for expenses that were paid on our behalf and the receivable from the general partner for expenses that we paid that were not allocated to the Partnership were as follows:



	September 30,		December 31,
	2013		2012
	(In thousands)
Due to affiliate	$	430	$	—
Due from affiliate	—		774

Expenses incurred and allocated to us by the general partner under our partnership agreement were as follows:



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(In thousands)
General and administrative expense allocation	$	794	$	2,600

Electricity Management Services Agreement. We entered into a consulting arrangement with EquiPower Resources Corp. to assist with managing DFW Midstream's electricity price risk. EquiPower Resources Corp. is an affiliate of Energy Capital Partners. Amounts paid for such services were as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Payments for electricity management consulting services	$	54	$	56	$	163	$	144

- 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

9 Months Ended

Sep. 30, 2013

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

Operating Leases. We lease various office space to support our operations and have determined that our leases are operating leases. Total rent expense related to operating leases, which is recognized in general and administrative expenses, was as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Total rent expense	$	312	$	189	$	819	$	504

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 would not individually or in the aggregate have a material adverse effect on its financial position or results of operations.

In August 2012, four former DFW Midstream employees (the "Plaintiffs") who, by virtue of their Class B membership in DFW Midstream Management LLC ("DFW Management"), filed a claim in the Court of Chancery of the State of Delaware against Summit Investments, Summit Holdings, DFW Midstream and DFW Management (collectively, the "Defendants") seeking dissolution and wind-up of DFW Midstream and DFW Management or, in the alternative, a repurchase of the Plaintiffs' net profits interests and other unspecified monetary damages. In September 2012, the Defendants filed a motion to dismiss all of Plaintiffs’ claims in this matter. The court heard oral arguments on the motion to dismiss in December 2012, and Defendants' motion to dismiss was granted in March 2013. In April 2013, the Plaintiffs voluntarily dismissed their appeal.

ACQUISITIONS

9 Months Ended

Sep. 30, 2013

Business Combinations [Abstract]

Acquisitions

ACQUISITIONS

Bison Gas Gathering System. On February 15, 2013, Summit Investments acquired BTE and subsequently contributed it to SMP Holdings. On June 4, 2013, SMP Holdings entered into a purchase and sale agreement with SMLP whereby SMLP acquired the Bison Gas Gathering system. The Bison Gas Gathering system was carved out from BTE and primarily gathers natural gas production from Mountrail and Burke counties in North Dakota under long-term contracts ranging from five years to 15 years. For additional information, see Notes 1, 5 and 6.

Summit Investments accounted for its purchase of BTE (the "BTE Transaction") under the acquisition method of accounting, whereby the various gathering systems' identifiable tangible and intangible assets acquired and liabilities assumed were recorded based on their fair values as of February 15, 2013. The intangible assets that were acquired are composed of gas gathering agreement contract values and right-of-way easements. Their fair values were determined based upon assumptions related to future cash flows, discount rates, asset lives, and projected capital expenditures to complete the various systems.

Because the Bison Drop Down was executed between entities under common control, SMLP recognized the acquisition of the Bison Gas Gathering system at historical cost which reflected Summit Investments recent fair value accounting for the BTE Transaction. Furthermore, due to the common control aspect, the Bison Drop Down was accounted for by SMLP on an “as if pooled” basis for all periods in which common control existed. Common control began on February 15, 2013 concurrent with Summit Investments' acquisition of BTE.

The fair values of the assets acquired and liabilities assumed as of February 15, 2013, were as follows:



	(In thousands)
Purchase price assigned to Bison Gas Gathering system			$	303,168
Current assets	$	5,705
Property, plant, and equipment	85,477
Intangible assets	164,502
Other noncurrent assets	2,187
Total assets acquired	257,871
Current liabilities	6,112
Other noncurrent liabilities	2,790
Total liabilities assumed	$	8,902
Net identifiable assets acquired			248,969
Goodwill			$	54,199

We believe that the goodwill recorded represents the incremental value of future cash flow potential attributed to estimated future gathering services within the Williston Basin.

The Bison Drop Down closed on June 4, 2013. The total acquisition purchase price of $248.9 million was funded with $200.0 million of borrowings under SMLP’s revolving credit facility and the issuance of $47.9 million of SMLP common units to SMP Holdings and $1.0 million of general partner interests to SMLP’s general partner. SMP Holdings had a net investment in the Bison Gas Gathering system of $303.2 million and received total consideration of $248.9 million from SMLP. As a result, SMLP recognized a capital contribution from SMP Holdings for the contribution of net assets in excess of consideration paid. See Notes 5 and 6 for additional information.

As noted above, SMLP's acquisition of the Bison Gas Gathering system was a transaction between commonly controlled entities which required that SMLP account for the acquisition in a manner similar to a pooling of interests. As a result, the historical financial statements of the Partnership and the Bison Gas Gathering system have been combined to reflect the historical operations, financial position and cash flows from the date common control began in February 2013. Revenues and net income for the previously separate entities and the combined amounts for the nine months ended September 30, 2013, as presented in these unaudited condensed consolidated financial statements follow.



	Nine months ended September 30, 2013
	(In thousands)
SMLP revenues	$	155,894
Bison Gas Gathering system revenues	17,614
Combined revenues	$	173,508

SMLP net income	$	27,239
Bison Gas Gathering system net income	52
Combined net income	$	27,291

See Notes 1, 5 and 6 for additional information.

Mountaineer Midstream. We completed the acquisition of Mountaineer Midstream from MarkWest for $210.0 million on June 21, 2013. The Mountaineer Midstream natural gas gathering and compression assets are located in the Appalachian Basin which includes the Marcellus Shale formation primarily in Doddridge County in northern West Virginia. The Mountaineer Midstream system consists of newly constructed, high-pressure gas gathering pipelines, certain rights-of-way associated with the pipeline, and two compressor stations. The assets gather natural gas under a long-term, fee-based contract with an affiliate of Antero Resources Corp.

The Mountaineer Acquisition was funded with $110.0 million of borrowings under the Partnership's revolving credit agreement and the issuance of $100.0 million of common and general partner interests to SMP Holdings. For the three months ended September 30, 2013, SMLP recorded $4.3 million of revenue and $1.3 million of net income related to Mountaineer Midstream. For the nine months ended September 30, 2013, SMLP recorded $4.7 million of revenue and $1.6 million of net income related to Mountaineer Midstream.

SMLP is accounting for the Mountaineer Acquisition under the acquisition method of accounting and is currently in the process of determining the assets acquired and the liabilities assumed. As of June 30, 2013, we preliminarily assigned the full $210.0 million purchase price to property plant and equipment. During the third quarter of 2013, we received additional information and, as a result, preliminarily assigned $158.3 million of the purchase price to property, plant and equipment, $27.1 million to contract intangibles, $6.5 million to rights-of-way and $18.1 million to goodwill. We have not completed the final purchase price allocation as of September 30, 2013, because we are waiting to receive additional information from MarkWest related to closing balance sheet and working capital adjustments and the finalization of the fair value estimates of the acquired assets and liabilities.

See Notes 1, 5 and 6 for additional information.

Unaudited Pro Forma Financial Information. The following unaudited pro forma financial information assumes that the acquisitions of Bison Midstream and Mountaineer Midstream occurred on January 1, 2012. The pro forma results for Bison Midstream were derived from revenues and net income in 2013 and 2012. The pro forma results for Mountaineer Midstream were derived from revenues and net income in 2013. Mountaineer Midstream was not operational until November 2012. The pro forma adjustments also reflect the impact of $310.0 million of incremental borrowings on our revolving credit facility and incremental depreciation and amortization expense associated with the acquired property, plant and equipment and contract intangibles as a result of the application of fair value accounting. Pro forma net income for the nine months ended September 30, 2013 has been adjusted to remove the impact of $2.5 million of nonrecurring transaction costs incurred during the nine months ended September 30, 2013.



	Three months ended September 30, 2012		Nine months ended September 30,
	Three months ended September 30, 2012		2013		2012
	(In thousands, except per-unit amounts)
Total Bison Midstream and Mountaineer Midstream revenues included in consolidated revenues	$	—	$	44,176	$	—
Total Bison Midstream and Mountaineer Midstream net income included in consolidated net income	—		911		—

Pro forma total revenues	$	50,731	$	185,659	$	141,372
Pro forma net income	6,014		24,316		16,549

Pro forma common EPU - basic and diluted			$	0.44
Pro forma subordinated EPU - basic and diluted			0.44

The unaudited pro forma financial information presented above is not necessarily indicative of what our financial position or results of operations would have been if the acquisitions of Bison Midstream and Mountaineer Midstream had occurred on January 1, 2012, or what SMLP’s financial position or results of operations will be for any future periods.

- 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
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Topic 805
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

Reclassification

Fair Value of Financial Instruments


•	Level 1. Inputs represent quoted prices in active markets for identical assets or liabilities;

•


•	Level 3. Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement).

Nonfinancial assets and liabilities initially measured at fair value include those acquired and assumed in connection with third-party business combinations.

A summary of the estimated fair value for financial instruments follows.



	September 30, 2013				December 31, 2012
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Revolving credit facility	$	265,050	$	265,050	$	199,230	$	199,230
Senior notes	300,000		308,500		—		—

Intangible Assets and Noncurrent Liability

Other Noncurrent Assets

Revenue Recognition

We obtain access to natural gas and provide services principally under contracts that contain one or both of the following arrangements:

•

Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis.

Unit Based Compensation

Income Taxes

Earnings per Unit

Comprehensive Income

Comprehensive Income. Comprehensive income is the same as net income for all periods presented.

Environmental Matters

Recent Accounting Pronouncements

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

9 Months Ended

Sep. 30, 2013

Accounting Policies [Abstract]

Summary of Estimated Fair Value for Financial instruments

A summary of the estimated fair value for financial instruments follows.



	September 30, 2013				December 31, 2012
	Carrying value		Estimated fair value (Level 2)		Carrying value		Estimated fair value (Level 2)
	(In thousands)
Revolving credit facility	$	265,050	$	265,050	$	199,230	$	199,230
Senior notes	300,000		308,500		—		—

PROPERTY, PLANT, AND EQUIPMENT, NET (Tables)

9 Months Ended

Sep. 30, 2013

Property, Plant and Equipment [Abstract]

Schedule of property, plant, and equipment, net

Details on property, plant, and equipment, net were as follows:



	Useful lives (In years)	September 30,			December 31,
	Useful lives (In years)	2013			2012
	(Dollars in thousands)
Gas gathering systems	30	$	618,528		$	427,449
Compressor stations and compression equipment	30	334,108			237,618
Construction in progress	n/a	50,381			45,919
Other	4-15	9,680			4,524
Total		1,012,697			715,510
Accumulated depreciation		(55,142		)	(33,517		)
Property, plant, and equipment, net		$	957,555		$	681,993

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

Depreciation expense related to property, plant, and equipment and capitalized interest were as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Depreciation expense	$	8,429	$	5,623	$	21,625	$	15,682
Capitalized interest	1,838		310		2,808		2,191

IDENTIFIABLE INTANGIBLE ASSETS AND NONCURRENT LIABILITY (Tables)

9 Months Ended

Sep. 30, 2013

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of identifiable intangible assets and a noncurrent liability, which are subject to amortization

Identifiable intangible assets and the noncurrent liability, which are subject to amortization, were as follows:



	September 30, 2013
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(5,847	)	$	18,348
Contract intangibles	16.8	429,575		(34,771		)	394,804
Rights-of-way	28.3	55,773		(4,116		)	51,657
Total amortizable intangible assets		$	509,543	$	(44,734	)	$	464,809

Unfavorable gas gathering contract	10.0	$	10,962	$	(4,358	)	$	6,604



	December 31, 2012
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
	(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(4,237	)	$	19,958
Contract intangibles	12.4	244,100		(14,504		)	229,596
Rights-of-way	28.3	38,848		(2,862		)	35,986
Total amortizable intangible assets		$	307,143	$	(21,603	)	$	285,540

Unfavorable gas gathering contract	10.0	$	10,962	$	(3,542	)	$	7,420

Schedule of recognized amortization expense within the statements of operations

We recognized amortization expense as follows:



	Three months ended September 30,						Nine months ended September 30,
	2013			2012			2013			2012
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	511		$	501		$	1,610		$	1,181
Amortization expense – contract intangibles	7,559			3,194			20,267			9,483
Amortization expense – rights-of-way	438			340			1,254			970
Amortization expense – unfavorable gas gathering contract	(247		)	(341		)	(816		)	(1,206		)

Schedule of estimated aggregate amortization of intangible assets and the noncurrent liability for each of the five succeeding fiscal years



	Assets		Liabilities
	(In thousands)
2013	$	8,801	$	378
2014	36,949		1,549
2015	39,628		1,650
2016	39,754		1,571
2017	38,316		1,456

Schedule of Goodwill

A rollforward of the consolidated balance of goodwill for the nine months ended September 30, 2013 follows.



	(In thousands)
Goodwill, beginning of period	$	45,478
Goodwill recognized in connection with the Bison Drop Down	54,199
Goodwill preliminarily recognized in connection with the Mountaineer Acquisition	18,089
Goodwill, end of period	$	117,766

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Tables)

9 Months Ended

Sep. 30, 2013

Business Acquisition [Line Items]

Schedule of Partner Units Activity

A rollforward of the number of common limited partner, subordinated limited partner and general partner units from December 31, 2012 to September 30, 2013 follows.



	Common	Subordinated	General partner	Total
Units, beginning of period	24,412,427	24,409,850	996,320	49,818,597
Units issued to SMP Holdings in connection with the Bison Drop Down	1,553,849	—	31,711	1,585,560
Units issued to SMP Holdings in connection with the Mountaineer Acquisition	3,107,698	—	63,422	3,171,120
Units issued	1,473	—	—	1,473
Units, end of period	29,075,447	24,409,850	1,091,453	54,576,750

Schedule of partnership target distributions

The following table illustrates the percentage allocations of available cash between the unitholders and our general partner based on the specified target distribution levels. The amounts set forth in the column Marginal Percentage Interest in Distributions are the percentage interests of our general partner and the unitholders in any available cash we distribute up to and including the corresponding amount in the column Total Quarterly Distribution Per Unit Target Amount. The percentage interests shown for our unitholders and our general partner for the minimum quarterly distribution are also applicable to quarterly distribution amounts that are less than the minimum quarterly distribution. The percentage interests set forth below for our general partner include its 2.0% general partner interest and assume that our general partner has contributed any additional capital necessary to maintain its 2.0% general partner interest, our general partner has not transferred its incentive distribution rights and that there are no arrearages on common units.



	Total quarterly distribution per unit target amount	Marginal percentage interest in distributions
	Total quarterly distribution per unit target amount	Unitholders	General partner
Minimum quarterly distribution	$0.40	98.0%	2.0%
First target distribution	$0.40 up to $0.46	98.0%	2.0%
Second target distribution	above $0.46 up to $0.50	85.0%	15.0%
Third target distribution	above $0.50 up to $0.60	75.0%	25.0%
Thereafter	above $0.60	50.0%	50.0%

Details of Cash Distributions

Details of cash distributions declared during 2013 follow.



Attributable to the quarter ended	Payment date	Per-unit distribution		Cash paid (or payable) to common unitholders		Cash paid (or payable) to subordinated unitholders		Cash paid (or payable) to general partner		Total distribution
		(Dollars in thousands, except per-unit amounts)
December 31, 2012	February 14, 2013	$	0.4100	$	10,009	$	10,008	$	408	$	20,425
March 31, 2013	May 15, 2013	0.4200		10,253		10,252		418		20,923
June 30, 2013	August 14, 2013	0.4350		12,647		10,618		475		23,740
September 30, 2013	November 14, 2013	0.4600		13,377		11,229		502		25,108

Bison Midstream

Business Acquisition [Line Items]

Schedule of Business Acquisition

In exchange for its $305.4 million net investment in Bison Midstream, SMLP paid SMP Holdings and the general partner total cash and unit consideration of $248.9 million. As a result of the contribution of net assets in excess of consideration, SMLP recognized a capital contribution from SMP Holdings. The details of total cash and unit consideration as well as the calculation of the capital contribution and its allocation to partners' capital follow.



	(Dollars in thousands)
SMP Holdings' net investment in Bison Midstream			$	305,449
Aggregate cash paid to SMP Holdings	$	200,000
Issuance of 1,553,849 SMLP common units to SMP Holdings	47,936
Issuance of 31,711 SMLP general partner units to the general partner	978
Total consideration			248,914
SMP Holdings' contribution of net assets in excess of consideration			$	56,535

Allocation of capital contribution:
General partner interest	$	1,131
Common limited partner interest	28,558
Subordinated limited partner interest	26,846
Partners' capital allocation			$	56,535

The fair values of the assets acquired and liabilities assumed as of February 15, 2013, were as follows:



	(In thousands)
Purchase price assigned to Bison Gas Gathering system			$	303,168
Current assets	$	5,705
Property, plant, and equipment	85,477
Intangible assets	164,502
Other noncurrent assets	2,187
Total assets acquired	257,871
Current liabilities	6,112
Other noncurrent liabilities	2,790
Total liabilities assumed	$	8,902
Net identifiable assets acquired			248,969
Goodwill			$	54,199

Mountaineer Midstream

Business Acquisition [Line Items]

Schedule of Business Acquisition

The allocation and valuation of units issued to SMP Holdings and the general partner to partially fund the Mountaineer Acquisition follow.



	(Dollars in thousands)
Issuance of 3,107,698 SMLP common units to SMP Holdings	$	98,000
Issuance of 63,422 SMLP general partner units to the general partner	2,000
Issuance of units in connection with the Mountaineer Acquisition	$	100,000

EARNINGS PER UNIT (Tables)

9 Months Ended

Sep. 30, 2013

Earnings Per Share [Abstract]

Schedule of earnings per Unit

The following table presents details on EPU.



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(Dollars in thousands, except per-unit amounts)
Net income	$	6,691	$	27,291
Less: net income attributable to SMP Holdings	—		52
Net income attributable to partners	6,691		27,239
Less: net income attributable to general partner	134		545
Net income attributable to limited partners	$	6,557	$	26,694

Net income attributable to common units	$	3,567	$	14,899

Weighted-average common units outstanding – basic	29,074,743		26,234,042
Earnings per common unit – basic	$	0.12	$	0.57

Weighted-average common units outstanding – diluted	29,227,041		26,352,234
Earnings per common unit – diluted	$	0.12	$	0.57

Net income attributable to subordinated units	$	2,990	$	11,795

Weighted-average subordinated units outstanding – basic and diluted	24,409,850		24,409,850
Earnings per subordinated unit – basic and diluted	$	0.12	$	0.48

UNIT-BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2013

Phantom and restricted units

MEMBERSHIP INTERESTS

Schedule of activity

The following table presents phantom and restricted unit activity:



	Units		Weighted-average grant date fair value
Nonvested phantom and restricted units, January 1, 2013	131,558		$	20.00
Phantom units granted	155,330		$	26.33
Restricted units granted	835		$	27.50
Phantom units forfeited	(4,041	)	$	25.99
Nonvested phantom and restricted units, September 30, 2013	283,682		$	23.41

Long-term Incentive Plan

MEMBERSHIP INTERESTS

Schedule of non-cash compensation expense recognized in general and administrative expense

compensation recognized in general and administrative expense related to awards under the LTIP was as follows:



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(In thousands)
SMLP unit-based compensation	$	829	$	1,970

DFW Net Profits Interests

MEMBERSHIP INTERESTS

Schedule of non-cash compensation expense recognized in general and administrative expense

compensation recognized in general and administrative expense related to the DFW Net Profits Interests was as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Class B membership interest unit-based compensation	$	—	$	75	$	17	$	874

CONCENTRATIONS OF RISK (Tables)

9 Months Ended

Sep. 30, 2013

Revenue | Customer concentration

CONCENTRATIONS OF RISK

Schedule of customers accounting for more than 10% of total revenues

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



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
Revenue:
Counterparty A	17	%	29	%	19	%	19	%
Counterparty B	16	%	29	%	18	%	27	%
Counterparty C	10	%	—	%	9	%	—	%
Counterparty D	10	%	—	%	9	%	—	%
Counterparty E	*		13	%	*		14	%

__________

* Less than 10%

Accounts receivable | Credit concentration

CONCENTRATIONS OF RISK

Schedule of customers accounting for more than 10% of total revenues

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



	September 30,		December 31,
	2013		2012
Accounts receivable:
Counterparty A	23	%	24	%
Counterparty B	21	%	38	%
Counterparty C	*		—	%
Counterparty D	*		—	%
Counterparty E	*		*

__________

* Less than 10%

RELATED-PARTY TRANSACTIONS (Tables)

9 Months Ended

Sep. 30, 2013

Schedules of Related Party Transactions



	September 30,		December 31,
	2013		2012
	(In thousands)
Due to affiliate	$	430	$	—
Due from affiliate	—		774

Expenses incurred and allocated to us by the general partner under our partnership agreement were as follows:



	Three months ended September 30, 2013		Nine months ended September 30, 2013
	(In thousands)
General and administrative expense allocation	$	794	$	2,600



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Payments for electricity management consulting services	$	54	$	56	$	163	$	144

COMMITMENTS AND CONTINGENCIES (Tables)

9 Months Ended

Sep. 30, 2013

Commitments and Contingencies Disclosure [Abstract]

Schedule of total rent expense related to operating leases

Total rent expense related to operating leases, which is recognized in general and administrative expenses, was as follows:



	Three months ended September 30,				Nine months ended September 30,
	2013		2012		2013		2012
	(In thousands)
Total rent expense	$	312	$	189	$	819	$	504

ACQUISITIONS (Tables)

9 Months Ended

Sep. 30, 2013

Business Acquisition [Line Items]

Business Acquisition, Pro Forma Information



	Three months ended September 30, 2012		Nine months ended September 30,
	Three months ended September 30, 2012		2013		2012
	(In thousands, except per-unit amounts)
Total Bison Midstream and Mountaineer Midstream revenues included in consolidated revenues	$	—	$	44,176	$	—
Total Bison Midstream and Mountaineer Midstream net income included in consolidated net income	—		911		—

Pro forma total revenues	$	50,731	$	185,659	$	141,372
Pro forma net income	6,014		24,316		16,549

Pro forma common EPU - basic and diluted			$	0.44
Pro forma subordinated EPU - basic and diluted			0.44

Bison Midstream

Business Acquisition [Line Items]

Fair Value of Assets Acquired and Liabilities Assumed



	(Dollars in thousands)
SMP Holdings' net investment in Bison Midstream			$	305,449
Aggregate cash paid to SMP Holdings	$	200,000
Issuance of 1,553,849 SMLP common units to SMP Holdings	47,936
Issuance of 31,711 SMLP general partner units to the general partner	978
Total consideration			248,914
SMP Holdings' contribution of net assets in excess of consideration			$	56,535

Allocation of capital contribution:
General partner interest	$	1,131
Common limited partner interest	28,558
Subordinated limited partner interest	26,846
Partners' capital allocation			$	56,535

The fair values of the assets acquired and liabilities assumed as of February 15, 2013, were as follows:



	(In thousands)
Purchase price assigned to Bison Gas Gathering system			$	303,168
Current assets	$	5,705
Property, plant, and equipment	85,477
Intangible assets	164,502
Other noncurrent assets	2,187
Total assets acquired	257,871
Current liabilities	6,112
Other noncurrent liabilities	2,790
Total liabilities assumed	$	8,902
Net identifiable assets acquired			248,969
Goodwill			$	54,199

Schedule of Revenue and Net Income Disclosures

Revenues and net income for the previously separate entities and the combined amounts for the nine months ended September 30, 2013, as presented in these unaudited condensed consolidated financial statements follow.



	Nine months ended September 30, 2013
	(In thousands)
SMLP revenues	$	155,894
Bison Gas Gathering system revenues	17,614
Combined revenues	$	173,508

SMLP net income	$	27,239
Bison Gas Gathering system net income	52
Combined net income	$	27,291

Mountaineer Midstream

Business Acquisition [Line Items]

Fair Value of Assets Acquired and Liabilities Assumed

The allocation and valuation of units issued to SMP Holdings and the general partner to partially fund the Mountaineer Acquisition follow.



	(Dollars in thousands)
Issuance of 3,107,698 SMLP common units to SMP Holdings	$	98,000
Issuance of 63,422 SMLP general partner units to the general partner	2,000
Issuance of units in connection with the Mountaineer Acquisition	$	100,000

ORGANIZATION AND BUSINESS OPERATIONS (Details)			1 Months Ended	9 Months Ended
ORGANIZATION AND BUSINESS OPERATIONS (Details)	Jun. 04, 2013	Oct. 03, 2012	Mar. 31, 2013	Sep. 30, 2013 segment shares	Dec. 31, 2012 shares
ORGANIZATION AND BUSINESS OPERATIONS
Common limited partner capital, units outstanding				29,073,974	24,412,427
General partner interests, units outstanding				1,091,453	996,320
Number of operating segments \| segment				4
Number of reportable segments \| segment				1
Holdings
ORGANIZATION AND BUSINESS OPERATIONS
Cumulative percentage ownership after all transactions		100.00%
DFW Midstream
ORGANIZATION AND BUSINESS OPERATIONS
Cumulative percentage ownership after all transactions		100.00%
Grand River Gathering, LLC
ORGANIZATION AND BUSINESS OPERATIONS
Cumulative percentage ownership after all transactions		100.00%
Summit Midstream Partners Holdings, LLC
ORGANIZATION AND BUSINESS OPERATIONS
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest			100.00%
SMP Holdings
ORGANIZATION AND BUSINESS OPERATIONS
General partner interests, units outstanding				1,091,453
Common units \| SMP Holdings
ORGANIZATION AND BUSINESS OPERATIONS
Common limited partner capital, units outstanding				14,691,397
Subordinated units \| SMP Holdings
ORGANIZATION AND BUSINESS OPERATIONS
Common limited partner capital, units outstanding				24,409,850
General partner
ORGANIZATION AND BUSINESS OPERATIONS
General partner interest (as a percent)	2.00%	2.00%	2.00%

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revolving credit facility, Carrying value	$ 265,050	$ 199,230
Senior notes, Carrying value	300,000	0
Fair value, Level 2 inputs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revolving credit facility, Estimated fair value (Level 2)	265,050	199,230
Senior notes, Estimated fair value (Level 2)	$ 308,500	$ 0

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNITNG POLICIES (Details 1)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Favorable gas gathering contract
Finite-Lived Intangible Assets [Line Items]
Useful lives	18 years 8 months 12 days	18 years 8 months 12 days
Favorable gas gathering contract \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful lives	10 years
Favorable gas gathering contract \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful lives	20 years
Other gas gathering contract \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful lives	10 years
Other gas gathering contract \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful lives	25 years
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Useful lives	28 years 3 months 18 days	28 years 3 months 18 days
Rights-of-way \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful lives	20 years
Rights-of-way \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful lives	30 years
Gathering systems
Finite-Lived Intangible Assets [Line Items]
Useful lives	30 years

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) - USD ($) $ in Millions			1 Months Ended	9 Months Ended
	Jun. 04, 2013	Oct. 03, 2012	Mar. 31, 2013	Sep. 30, 2013
Significant Accounting Policies [Line Items]
Shortfall payments billed				$ 24.1
Shortfall payments billed and included in accounts receivable				$ 1.1
General partner
Significant Accounting Policies [Line Items]
General partner interest (as a percent)	2.00%	2.00%	2.00%
Minimum
Significant Accounting Policies [Line Items]
Period to utilize shortfall payments to offset gathering fees to the extent that customer's throughput volumes exceed its MVC				12 months
Period to utilize the current portion of shortfall payments to offset gathering fees to the extent that customer's throughput volumes exceed its MVC				1 month
Maximum
Significant Accounting Policies [Line Items]
Period to utilize shortfall payments to offset gathering fees to the extent that customer's throughput volumes exceed its MVC				8 years
Period to utilize the current portion of shortfall payments to offset gathering fees to the extent that customer's throughput volumes exceed its MVC				8 years

PROPERTY, PLANT, AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
PROPERTY, PLANT, AND EQUIPMENT, NET
Gross	$ 1,012,697		$ 1,012,697		$ 715,510
Less accumulated depreciation	(55,142)		(55,142)		(33,517)
Property, plant, and equipment, net	957,555		957,555		681,993
Depreciation expense	8,429	$ 5,623	21,625	$ 15,682
Capitalized interest	1,838	$ 310	$ 2,808	$ 2,191
Gas gathering system
PROPERTY, PLANT, AND EQUIPMENT, NET
Useful lives			30 years
Gross	618,528		$ 618,528		427,449
Compressor stations and compression equipment
PROPERTY, PLANT, AND EQUIPMENT, NET
Useful lives			30 years
Gross	334,108		$ 334,108		237,618
Construction in progress
PROPERTY, PLANT, AND EQUIPMENT, NET
Gross	50,381		50,381		45,919
Other
PROPERTY, PLANT, AND EQUIPMENT, NET
Gross	$ 9,680		$ 9,680		$ 4,524
Other \| Minimum
PROPERTY, PLANT, AND EQUIPMENT, NET
Useful lives			4 years
Other \| Maximum
PROPERTY, PLANT, AND EQUIPMENT, NET
Useful lives			15 years

IDENTIFIABLE INTANGIBLE ASSETS AND NONCURRENT LIABILITY (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount		$ 509,543		$ 509,543		$ 307,143
Accumulated amortization		(44,734)		(44,734)		(21,603)
Total intangible assets, net		464,809		$ 464,809		$ 285,540
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		(4,358)		(4,358)		(3,542)
Unfavorable gas gathering contract, Net		6,604		6,604		7,420
Amortization expense
Amortization expense - unfavorable contract		(247)	$ (341)	(816)	$ (1,206)
Assets
2013		8,801		8,801
2014		36,949		36,949
2015		39,628		39,628
2016		39,754		39,754
2017		38,316		38,316
Liabilities
2013		378		378
2014		1,549		1,549
2015		1,650		1,650
2016		1,571		1,571
2017		1,456		1,456
Goodwill [Roll Forward]
Goodwill, beginning balance				45,478
Goodwill, ending balance		117,766		117,766		45,478
Mountaineer Midstream
Goodwill [Roll Forward]
Goodwill, beginning balance		18,100
Goodwill recognized in connection with the Bison Drop Down				18,089
Goodwill, ending balance	$ 18,100
Grand River Gathering, LLC
Goodwill [Roll Forward]
Goodwill, beginning balance					45,500	$ 45,500
Bison Midstream
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 54,199
Goodwill recognized in connection with the Bison Drop Down				54,199
Goodwill, ending balance		54,200		$ 54,200
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		(5,847)		(5,847)		(4,237)
Total intangible assets, net		18,348		18,348		$ 19,958
Amortization expense
Amortization expense		511	501	$ 1,610	1,181
Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Useful lives				16 years 9 months 15 days		12 years 4 months 24 days
Gross carrying amount		429,575		$ 429,575		$ 244,100
Accumulated amortization		(34,771)		(34,771)		(14,504)
Total intangible assets, net		394,804		394,804		$ 229,596
Amortization expense
Amortization expense		7,559	3,194	$ 20,267	9,483
Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Useful lives				28 years 3 months 18 days		28 years 3 months 18 days
Gross carrying amount		55,773		$ 55,773		$ 38,848
Accumulated amortization		(4,116)		(4,116)		(2,862)
Total intangible assets, net		51,657		51,657		$ 35,986
Amortization expense
Amortization expense		$ 438	$ 340	$ 1,254	$ 970

LONG-TERM DEBT (Details) - USD ($)		1 Months Ended	9 Months Ended
LONG-TERM DEBT (Details) - USD ($)	Nov. 01, 2013	Jun. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	May 31, 2012
REVOLVING CREDIT FACILITY
Revolving credit facility			$ 265,050,000		$ 199,230,000
Senior unsecured notes			300,000,000		0
Total long-term debt			565,050,000		$ 199,230,000
Repayments of Lines of Credit		$ 294,200,000	294,180,000	$ 15,770,000
Bison Midstream
REVOLVING CREDIT FACILITY
Revolving credit facility			200,000,000.0
Mountaineer Midstream
REVOLVING CREDIT FACILITY
Revolving credit facility			110,000,000.0
Revolving credit facility
REVOLVING CREDIT FACILITY
Defaults on revolving credit facility			$ 0
Revolving credit facility \| Holdings
REVOLVING CREDIT FACILITY
Variable rate basis			LIBOR
Applicable margin (as a percent)			3.25%
Weighted-average interest rate (as a percent)			3.43%		2.98%
Unused portion under the facility			$ 334,900,000
Commitment fee on unused portion of the facility (as a percent)			0.50%
Period that cumulative lease payment obligations may not exceed specified amount under terms of covenants			12 months
Trailing period used in calculating the ratio of EBITDA to net interest expense			12 months
Trailing period used in calculating the ratio of total indebtedness to consolidated EBITDA			12 months
Revolving credit facility \| Holdings \| Minimum
REVOLVING CREDIT FACILITY
Ratio of consolidated EBITDA to net interest expense			2.5
Revolving credit facility \| Holdings \| Maximum
REVOLVING CREDIT FACILITY
Cumulative lease payment obligations allowable under terms of covenants			$ 30,000,000.0
Ratio of total indebtedness to consolidated EBITDA			5.0
Ratio of total indebtedness to consolidated EBITDA, for a specified period following certain acquisitions			5.5
Period following certain acquisitions, for which higher ratio of total indebtedness to consolidated EBITDA is to be maintained			6 months
Revolving credit facility \| Senior Secured Debt
REVOLVING CREDIT FACILITY
Senior secured revolving credit facility, total commitments			$ 600,000,000.0			$ 550,000,000.0
Revolving credit facility \| Senior Secured Debt \| Subsequent Event
REVOLVING CREDIT FACILITY
Senior secured revolving credit facility, total commitments	$ 700,000,000.0
Interest rate reduction	0.75%
Revolving credit facility \| Senior Secured Debt \| Minimum \| Subsequent Event
REVOLVING CREDIT FACILITY
Commitment fee on unused portion of the facility (as a percent)	0.30%
Revolving credit facility \| Senior Secured Debt \| Maximum \| Subsequent Event
REVOLVING CREDIT FACILITY
Commitment fee on unused portion of the facility (as a percent)	0.50%
Revolving credit facility \| Senior Secured Debt \| LIBOR \| Minimum \| Subsequent Event
REVOLVING CREDIT FACILITY
Applicable margin (as a percent)	1.75%
Revolving credit facility \| Senior Secured Debt \| LIBOR \| Maximum \| Subsequent Event
REVOLVING CREDIT FACILITY
Applicable margin (as a percent)	2.75%
Revolving credit facility \| Senior Secured Debt \| Accordion provision
REVOLVING CREDIT FACILITY
Senior secured revolving credit facility, total commitments			$ 50,000,000.0
Revolving credit facility \| Senior Secured Debt \| Accordion provision \| Subsequent Event
REVOLVING CREDIT FACILITY
Senior secured revolving credit facility, total commitments	$ 200,000,000.0

LONG-TERM DEBT LONG-TERM DEBT (Senior Note) (Details) - USD ($) $ in Thousands		9 Months Ended
	Jun. 30, 2013	Sep. 30, 2013	Jun. 17, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Senior unsecured notes		$ 300,000		$ 0
Senior Notes
Debt Instrument [Line Items]
Senior unsecured notes			$ 300,000
Senior note, stated interst rate			7.50%
Debt issuance costs	$ 7,300
Period to complete exchange offer	365 days
Event of default, period of nonpayment	30 days
Event of default, period of noncompliance with SEC filings	180 days
Event of default, period of noncompliance with indenture agreements	30 days
Event of default, failure to pay judgments (more than)	$ 20,000
Event of default, Percentage of debt holders Required to declare all notes due and payable	25.00%
Senior Notes \| Maximum
Debt Instrument [Line Items]
Debt Instrument, Increase (Decrease) in Interest Rate, Stated Percentage	1.00%
Senior Notes \| Term 1
Debt Instrument [Line Items]
Debt Instrument, Increase (Decrease) in Interest Rate, Stated Percentage	0.25%
Exchange offer not declared effective, term 1	90 days
Senior Notes \| Subsequent Terms
Debt Instrument [Line Items]
Debt Instrument, Increase (Decrease) in Interest Rate, Stated Percentage	0.25%
Exchange offer not declared effective, subsequent terms	90 days
Senior Notes \| Prior to July 1 2016
Debt Instrument [Line Items]
Limit on redemption as a percentage of principal		35.00%
Redemption price as a percentage of principal		107.50%
Senior Notes \| On or After July 1 2016
Debt Instrument [Line Items]
Redemption price as a percentage of principal		105.625%
Senior Notes \| July 1 2019
Debt Instrument [Line Items]
Redemption price as a percentage of principal		100.00%
Finance Corp.
Debt Instrument [Line Items]
Cumulative percentage ownership in subsidiary		100.00%

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Schedule of Units) (Details)	9 Months Ended
	Sep. 30, 2013 shares
Class of Stock [Line Items]
Common limited partner capital units outstanding, beginning balance	24,412,427
Subordinated limited partner capital units outstanding, begining balance	24,409,850
General partner interests units outstanding, beginning balance	996,320
Partner capital units outstanding, beginning balance	49,818,597.000
Common limited partner capital units outstanding, ending balance	29,073,974
Subordinated limited partner capital units outstanding, ending balance	24,409,850
General partner interests units outstanding, ending balance	1,091,453
Limited Partners' Capital Account, Units Issued During Period	1,473.000
Partner capital units outstanding, ending balance	54,576,750
Bison Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	1,585,560.00
Mountaineer Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	3,171,120.00
Common
Class of Stock [Line Items]
Common limited partner capital units outstanding, beginning balance	24,412,427
Common limited partner capital units outstanding, ending balance	29,075,447
Limited Partners' Capital Account, Units Issued During Period	1,473
Common \| Bison Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	1,553,849
Common \| Mountaineer Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	3,107,698
Subordinated
Class of Stock [Line Items]
Subordinated limited partner capital units outstanding, begining balance	24,409,850
Subordinated limited partner capital units outstanding, ending balance	24,409,850
Subordinated \| Bison Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	0
Subordinated \| Mountaineer Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	0
General partner
Class of Stock [Line Items]
General partner interests units outstanding, beginning balance	996,320
General partner interests units outstanding, ending balance	1,091,453
General partner \| Bison Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	31,711
General partner \| Mountaineer Midstream
Class of Stock [Line Items]
Units issued in connection with acquisition	63,422

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Bison Acquisition) (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 04, 2013	Jun. 03, 2013	Oct. 03, 2012	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition [Line Items]
Transaction costs						$ 123	$ 1,739	$ 2,549	$ 1,972
Net assets in excess of consideration paid	$ 56,535							56,535	$ 0
General partner
Business Acquisition [Line Items]
General partner interest (as a percent)	2.00%		2.00%		2.00%
Bison Midstream
Business Acquisition [Line Items]
Cumulative percentage ownership after all transactions				100.00%
Volume weighted average share price, term		5 days
Volume weighted average share price		$ 31.53
Cost of acquired entity, cash paid	$ 200,000
Units issued to acquire entity								$ 200,000
Units issued in connection with acquisition								1,585,560.00
Net assets in excess of consideration paid								$ 0
Closing unit price	$ 30.85
SMP Holdings' net investment in Bison Midstream	$ 305,449
Bison Midstream \| General partner
Business Acquisition [Line Items]
Units issued to acquire entity								(978)
Net assets in excess of consideration paid	1,131							$ 1,131
Limited partners, Common \| Bison Midstream
Business Acquisition [Line Items]
Units issued to acquire entity	(47,936)
Units issued in connection with acquisition								1,553,849
General Partner Units \| Bison Midstream
Business Acquisition [Line Items]
Units issued to acquire entity	(978)
Units issued in connection with acquisition								31,711
Limited Partner Common and General Partner Units \| Bison Midstream
Business Acquisition [Line Items]
Units issued to acquire entity				$ (50,000)
SMP Holdings' equity in Bison Midstream \| Bison Midstream
Business Acquisition [Line Items]
Cost of acquired entity, cash paid	200,000
Units issued to acquire entity	$ 248,914							$ 248,914
Net assets in excess of consideration paid								$ (56,535)

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Mountaineer Acquisition) (Details) - Mountaineer Midstream - USD ($) $ / shares in Units, $ in Thousands				9 Months Ended
	Jun. 21, 2013	Jun. 04, 2013	Jun. 03, 2013	Sep. 30, 2013
Business Acquisition [Line Items]
Cost of acquired entity, purchase price	$ 210,000	$ 210,000
Cost of acquired entity, cash paid	110,000	110,000
Units issued to acquire entity		100,000		$ 100,000
Volume weighted average share price, term			5 days
Volume weighted average share price			$ 31.53
Units issued in connection with acquisition				3,171,120.00
Cost of acquired entity, equity interests issued and issuable	$ 100,000	100,000
Limited partners, Common
Business Acquisition [Line Items]
Units issued to acquire entity		98,000		$ 98,000
Units issued in connection with acquisition				3,107,698
General Partner Units
Business Acquisition [Line Items]
Units issued to acquire entity		$ 2,000
Units issued in connection with acquisition				63,422

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Thousands					9 Months Ended
	Oct. 24, 2013	Aug. 14, 2013	May 15, 2013	Feb. 14, 2013	Sep. 30, 2013	Sep. 30, 2012
Distribution Made to Limited Partner [Line Items]
Per-unit distribution		$ 0.004350	$ 0.004200	$ 0.004100
Distributions to unitholders		$ 23,740	$ 20,923	$ 20,425	$ 65,088	$ 0
Subsequent Event
Distribution Made to Limited Partner [Line Items]
Per-unit distribution	$ 0.004600
Distributions to unitholders, payable	$ 25,108
Limited partners, Common
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders		12,647	10,253	10,009
Limited partners, Common \| Subsequent Event
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders, payable	13,377
Subordinated
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders		10,618	10,252	10,008
Subordinated \| Subsequent Event
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders, payable	11,229
General Partner Units
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders		$ 475	$ 418	$ 408
General Partner Units \| Subsequent Event
Distribution Made to Limited Partner [Line Items]
Distributions to unitholders, payable	$ 502

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Subordination and Cash Distribution Policy) (Details) - $ / shares			1 Months Ended	9 Months Ended
	Jun. 04, 2013	Oct. 03, 2012	Mar. 31, 2013	Sep. 30, 2013
Schedule of Partners' Capital [Line Items]
Maximum period following end of quarter to distribute all available cash				45 days
General partner
Schedule of Partners' Capital [Line Items]
General partner interest (as a percent)	2.00%	2.00%	2.00%
Condition one
Schedule of Partners' Capital [Line Items]
Minimum quarterly distribution (in dollars per share)				$ 1.60
Term for condition to be met to end subordination period				3 years
Condition one \| General partner
Schedule of Partners' Capital [Line Items]
General partner interest (as a percent)				2.00%
Condition two
Schedule of Partners' Capital [Line Items]
Minimum quarterly distribution (in dollars per share)				$ 2.40
Percent of minimum distribution				150.00%
Condition two \| General partner
Schedule of Partners' Capital [Line Items]
General partner interest (as a percent)				2.00%
Subordinated units
Schedule of Partners' Capital [Line Items]
Common unit per subordinated unit upon conversion at end of subordination period (in shares)				1

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Minimum Quarterly Distribution) (Details)	9 Months Ended
	Sep. 30, 2013 $ / shares
Equity [Abstract]
Minimum quarterly distributions (in dollars per share)	$ 0.40
Minimum annual distributions (in dollars per share)	$ 1.60

PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Partnership Target Distributions) (Details)	9 Months Ended
	Sep. 30, 2013 $ / shares
Minimum quarterly distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	$ 0.4
Thereafter
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.60
Minimum \| First target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.40
Minimum \| Second target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.46
Minimum \| Third target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.50
Maximum \| First target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.46
Maximum \| Second target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	0.5
Maximum \| Third target distribution
Schedule of Partnership Target Distributions [Line Items]
Total quarterly distribution per unit target amount	$ 0.6
Unitholders \| Minimum quarterly distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	98.00%
Unitholders \| First target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	98.00%
Unitholders \| Second target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	85.00%
Unitholders \| Third target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	75.00%
Unitholders \| Thereafter
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	50.00%
General partner
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	2.00%
Quarterly distributions per unit, incentive threshold	$ 0.46
General partner \| Minimum quarterly distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	2.00%
General partner \| First target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	2.00%
General partner \| Second target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	15.00%
General partner \| Third target distribution
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	25.00%
General partner \| Thereafter
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions	50.00%
General partner \| Maximum
Schedule of Partnership Target Distributions [Line Items]
Percentage interest in distributions in excess of incentive threshold	50.00%

EARNINGS PER UNIT (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 6,691	$ 7,396	$ 27,291	$ 24,112
Less: net income attributable to SMP Holdings	0		(52)
Net income attributable to partners	6,691		27,239
Less: net income attributable to general partner	(134)		(545)
Net income attributable to limited partners	$ 6,557		$ 26,694
Weighted-average common units outstanding – basic (in units)	29,074,743		26,234,042
Earnings per common unit – basic (in dollars per unit)	$ 0.12		$ 0.57
Weighted-average common units outstanding – diluted (in units)	29,227,041		26,352,234
Earnings per common unit – diluted (in dollars per unit)	$ 0.12		$ 0.57
Weighted-average subordinated units outstanding – basic and diluted (in units)	24,409,850		24,409,850
Earnings per subordinated unit – basic and diluted (in dollars per unit)	$ 0.12		$ 0.48
Phantom and restricted units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental units attributable to share-based payment arrangements	152,298		118,192
Limited partners, Common
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income			$ 13,691	0
Net income attributable to limited partners	$ 3,567		14,899
Subordinated
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income			13,003	$ 0
Net income attributable to limited partners	$ 2,990		$ 11,795

UNIT-BASED COMPENSATION (Details) $ / shares in Units, $ in Thousands	3 Months Ended		7 Months Ended	9 Months Ended
	Sep. 30, 2013 USD ($) $ / shares shares	Sep. 30, 2012 USD ($)	Apr. 30, 2013 USD ($) holder shares	Sep. 30, 2013 USD ($) $ / shares shares	Sep. 30, 2012 USD ($)
Other disclosures
Payment to acquire vested net profit interests \| $				$ 11,957	$ 0
Long-term Incentive Plan
Weighted-average grant date fair value
Non-cash compensation expense (in dollars) \| $	$ 829
Other disclosures
Unit-based compensation \| $				$ 1,970
Common Units \| Long-term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units reserved for issuance pursuant to LTIP	5,000,000.0			5,000,000.0
Units available for future issuance	4,700,000			4,700,000
Phantom Units
Phantom and Restricted Unit Activity
Nonvested phantom and restricted units, beginning of period (in shares)				131,558
Units granted (in shares)				155,330
Units forfeited (in shares)				(4,041)
Nonvested phantom and restricted units, end of period (in shares)	283,682			283,682
Weighted-average grant date fair value
Nonvested, Weighted-average grant date fair value, beginning \| $ / shares				$ 20.00
Units granted, Weighted-average grant date fair value \| $ / shares				26.33
Units forfeited, Weighted-average grant date fair value \| $ / shares				25.99
Nonvested, Weighted-average grant date fair value, ending \| $ / shares	$ 23.41			$ 23.41
Award vesting period				3 years
Phantom Units \| Granted in March 2013
Weighted-average grant date fair value
Unrecognized non-cash compensation expense \| $	$ 4,400			$ 4,400
Remaining expected weighted-average vesting period of recognition of incremental non-cash compensation expense				2 years 11 months
Phantom Units \| Granted in October 2012
Phantom and Restricted Unit Activity
Units forfeited (in shares)				0
Restricted Units
Phantom and Restricted Unit Activity
Units granted (in shares)				835
Weighted-average grant date fair value
Units granted, Weighted-average grant date fair value \| $ / shares				$ 27.50
DFW Net Profits Interests
Weighted-average grant date fair value
Non-cash compensation expense (in dollars) \| $	$ 0	$ 75		$ 17	$ 874
Other disclosures
Number of holders of net profit interest \| holder			7
Payment to acquire vested net profit interests \| $			$ 12,200
SMLP Restricted Units
Other disclosures
Restricted units exchanged for unvested net profit interests			7,393

CONCENTRATIONS OF RISK (Details)	3 Months Ended		9 Months Ended		12 Months Ended
CONCENTRATIONS OF RISK (Details)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Counterparty A \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage	17.00%	29.00%	19.00%	19.00%
Counterparty A \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage			23.00%		24.00%
Counterparty B \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage	16.00%	29.00%	18.00%	27.00%
Counterparty B \| Accounts receivable \| Credit concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage			21.00%		38.00%
Counterparty C \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage	10.00%		9.00%
Counterparty D \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage	10.00%		9.00%
Counterparty E [Member] \| Revenue \| Customer concentration
CONCENTRATIONS OF RISK
Total revenues, major customer percentage		13.00%		14.00%

RELATED-PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Dec. 31, 2012
RELATED-PARTY TRANSACTIONS
Due to affiliate	$ 430			$ 430	$ 0
Due from affiliate	0			0	774
General partner
RELATED-PARTY TRANSACTIONS
Due to affiliate	430			430	0
Due from affiliate	0			0	$ 774
General and administrative expense allocation	794			2,600
Equipower
RELATED-PARTY TRANSACTIONS
Payments for electricity management consulting services	$ 54	$ 56	$ 144	$ 163

COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands	Aug. 31, 2012 employee	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)
Commitments and contingencies
Total rent expense related to operating leases \| $		$ 312	$ 189	$ 819	$ 504
Former DFW Midstream Employee Claim
Commitments and contingencies
Number of plaintiffs \| employee	4

ACQUISITIONS (Bison Midstream) (Details) - USD ($) $ in Thousands		1 Months Ended	9 Months Ended
	Jun. 04, 2013	Jun. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Goodwill			$ 117,766	$ 45,478
Gas Gathering Contract \| Minimum
Business Acquisition [Line Items]
Useful lives			10 years
Gas Gathering Contract \| Maximum
Business Acquisition [Line Items]
Useful lives			25 years
Bison Midstream
Business Acquisition [Line Items]
Cost of acquired entity, purchase price	$ 248,900
Purchase price assigned to Bison Gas Gathering system	303,168
Current assets	5,705
Property, plant, and equipment	85,477
Intangible assets	164,502
Other noncurrent assets	2,187
Total assets acquired	257,871
Current liabilities	6,112
Other noncurrent liabilities	2,790
Total liabilities assumed	8,902
Net identifiable assets acquired	248,969
Goodwill	54,199		$ 54,200
Cost of acquired entity, cash paid	200,000
Units issued to acquire entity			200,000
Purchase price assigned to Bison Gas Gathering system			303,168
Bison Midstream \| Limited partners, Common
Business Acquisition [Line Items]
Cost of acquired entity, equity interests issued and issuable	47,900
Units issued to acquire entity	(47,936)
Bison Midstream \| General Partner Units
Business Acquisition [Line Items]
Cost of acquired entity, equity interests issued and issuable	1,000
Units issued to acquire entity	(978)
Bison Midstream \| SMP Holdings' equity in Bison Midstream
Business Acquisition [Line Items]
Cost of acquired entity, purchase price	248,900
Cost of acquired entity, cash paid	200,000
Units issued to acquire entity	248,914		248,914
Purchase price assigned to Bison Gas Gathering system	$ 303,200		$ 303,168
Bison Midstream \| Gas Gathering Contract \| Minimum
Business Acquisition [Line Items]
Useful lives		5 years
Bison Midstream \| Gas Gathering Contract \| Maximum
Business Acquisition [Line Items]
Useful lives		15 years

ACQUISITIONS (Revenue and Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition [Line Items]
Revenues	$ 63,096	$ 40,975	$ 173,508	$ 116,865
Net income	$ 6,691	$ 7,396	27,291	$ 24,112
Summit Midstream Partners, LP
Business Acquisition [Line Items]
Revenues			155,894
Net income			27,239
Bison Midstream, LLC
Business Acquisition [Line Items]
Revenues			17,614
Net income			$ 52

ACQUISITIONS (Mountaineer Midstream) (Details) $ in Thousands			3 Months Ended	9 Months Ended
	Jun. 21, 2013 USD ($) compressor_station	Jun. 04, 2013 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2013 USD ($)	Jun. 30, 2013 USD ($)	Dec. 31, 2012 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 117,766	$ 117,766		$ 45,478
Mountaineer Midstream
Business Acquisition [Line Items]
Cost of acquired entity, purchase price	$ 210,000	$ 210,000
Number of compressor stations acquired \| compressor_station	2
Cost of acquired entity, cash paid	$ 110,000	110,000
Cost of acquired entity, equity interests issued and issuable	$ 100,000	$ 100,000
Mountaineer Midstream revenues since acquisition			4,300	4,700
Mountaineer Midstream net income since acquisition			$ 1,300	$ 1,600
Purchase price assigned, property, plant, and equipment					$ 158,300
Goodwill					18,100
Mountaineer Midstream \| Contract intangibles
Business Acquisition [Line Items]
Purchase price assigned, intagibles assets					27,100
Mountaineer Midstream \| Rights-of-way
Business Acquisition [Line Items]
Purchase price assigned, intagibles assets					$ 6,500

ACQUISITIONS (Pro Forma) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma total revenues	$ 50,731	$ 185,659	$ 141,372
Pro forma net income	6,014	$ 24,316	16,549
Limited partners, Common
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma EPU, basic and diluted		$ 0.44
Subordinated units
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma EPU, basic and diluted		$ 0.44
Acquisition-related Costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma effect of nonrecurring transaction costs incurred on net income		$ 2,500
Bison Midstream and Mountaineer Midstream
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Incremental borrowings on revolving credit facility		310,000
Pro forma total revenues	0	44,176	0
Pro forma net income	$ 0	$ 911	$ 0

Label	Element	Value
Bison Midstream [Member] \| Limited Partner Subordinated [Member]
Partners' Capital Account, Net Assets in Excess of Consideration Paid	smlp_PartnersCapitalAccountNetAssetsinExcessofConsiderationPaid	$ 26,846,000
Bison Midstream [Member] \| Limited Partner Common [Member]
Partners' Capital Account, Net Assets in Excess of Consideration Paid	smlp_PartnersCapitalAccountNetAssetsinExcessofConsiderationPaid	$ 28,558,000
DFW Net Profits Interests [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	0