UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL (USD $) In Thousands, unless otherwise specified	Total	SMLP units	Class B Units	Summit Investments' equity in contributed subsidiaries	Summit Investments' equity in contributed subsidiaries Class B Units	Limited partners, Common	Limited partners, Common SMLP units	Limited partners, Common Class B Units	Limited partners, Subordinated	General partner	Bison Midstream	Bison Midstream Summit Investments' equity in contributed subsidiaries	Bison Midstream Limited partners, Common	Bison Midstream Limited partners, Subordinated	Bison Midstream General partner	Mountaineer Midstream	Mountaineer Midstream Limited partners, Common	Mountaineer Midstream General partner
Beginning balance at Dec. 31, 2012	$ 1,030,248			$ 211,001		$ 418,856			$ 380,169	$ 20,222
Members Interest Increase (Decrease) [Roll Forward]
Net income	22,630			2,082		10,127			10,010	411
Unit-based compensation		1,141	261		244		1,141	17
Consolidation of Bison Midstream net assets	303,168			303,168
Contribution from Summit Investments to Bison Midstream											2,229	2,229
Units issued to acquire entity											(200,000)	(248,914)	47,936		978	100,000	98,000	2,000
Contribution of net assets from Summit Investments in excess of consideration paid for Bison Midstream	56,535										0	(56,535)	28,558	26,846	1,131
Cash advance from Summit Investments to contributed subsidiaries	(2,243)			(2,243)
Expense paid by Summit Investments	4,762			4,762
Partners' Capital Account, Capitalized Interest Allocated To Affiliates	109			109
Distributions to unitholders	(41,348)					(20,262)			(20,260)	(826)
Repurchase of DFW Net Profit Interests	(11,957)					(5,859)			(5,859)	(239)
Ending balance at Jun. 30, 2013	1,209,000			215,903		578,514			390,906	23,677
Beginning balance at Dec. 31, 2013	1,201,737			232,594		566,532			379,287	23,324
Members Interest Increase (Decrease) [Roll Forward]
Net income	10,409			2,828		3,634			2,715	1,232
Unit-based compensation	2,424					2,424
Tax withholdings on vested SMLP LTIP awards	(656)					(656)
Issuance of common units, net of offering costs	197,989					197,989
Contribution from general partner	4,235									4,235
Contribution of net assets from Summit Investments in excess of consideration paid for Bison Midstream	0
Purchase of Red Rock Gathering	(305,000)			(305,000)
Excess of purchase price over acquired carrying value of Red Rock Gathering	0			63,183		(36,228)			(25,691)	(1,264)
Cash advance from Summit Investments to contributed subsidiaries	1,982			1,982
Expense paid by Summit Investments	4,413			4,413
Repurchase of SMLP LTIP units		(228)					(228)
Distributions to unitholders	(56,749)					(31,169)			(23,922)	(1,658)
Ending balance at Jun. 30, 2014	$ 1,060,556			$ 0		$ 702,298			$ 332,389	$ 25,869