CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Gathering services and related fees	$ 394,427,000	$ 345,961,000	$ 337,819,000
Natural gas, NGLs and condensate sales	68,459,000	35,833,000	42,079,000
Other revenues	25,855,000	20,568,000	20,659,000
Total revenues	488,741,000	402,362,000	400,557,000
Costs and expenses:
Cost of natural gas and NGLs	57,237,000	27,421,000	31,398,000
Operation and maintenance	93,882,000	95,334,000	94,986,000
General and administrative	54,681,000	52,410,000	45,108,000
Depreciation and amortization	115,475,000	112,239,000	105,117,000
Transaction costs	73,000	1,321,000	1,342,000
Environmental remediation	0	0	21,800,000
Loss (gain) on asset sales, net	527,000	93,000	(172,000)
Long-lived asset impairment	188,702,000	1,764,000	9,305,000
Goodwill impairment	0	0	248,851,000
Total costs and expenses	510,577,000	290,582,000	557,735,000
Other income	298,000	116,000	2,000
Interest expense	(68,131,000)	(63,810,000)	(59,092,000)
Early extinguishment of debt	(22,039,000)	0	0
Deferred Purchase Price Obligation	200,322,000	(55,854,000)	0
Income (loss) before income taxes and loss from equity method investees	88,614,000	(7,768,000)	(216,268,000)
Income tax (expense) benefit	(341,000)	(75,000)	603,000
Loss from equity method investees	(2,223,000)	(30,344,000)	(6,563,000)
Net income (loss)	86,050,000	(38,187,000)	(222,228,000)
Net income (loss) attributable to Summit Investments	0	2,745,000	(30,016,000)
Net income (loss) attributable to noncontrolling interest	363,000	(14,000)	0
Net income (loss) attributable to SMLP	85,687,000	(40,918,000)	(192,212,000)
Less net income (loss) attributable to General Partner, including IDRs	10,202,000	7,261,000	3,398,000
Net income (loss) attributable to limited partners	75,485,000	(48,179,000)	(195,610,000)
Common units
Costs and expenses:
Net income (loss) attributable to limited partners	$ 71,922,000	$ (48,179,000)	$ (195,610,000)
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0.99	$ (0.71)	$ (3.20)
Diluted (in dollars per share)	$ 0.98	$ (0.71)	$ (3.20)
Weighted-average limited partner units outstanding:
Basic (shares)	72,705	68,264	39,217
Diluted (shares)	73,047	68,264	39,217
Series A Preferred Units
Costs and expenses:
Net income (loss) attributable to limited partners	$ 3,563,000	$ 0	$ 0
Subordinated Units
Costs and expenses:
Net income (loss) attributable to limited partners	$ 0	$ 0	$ (70,173,000)
Earnings (loss) per limited partner unit:
Basic (in dollars per share)	$ 0	$ 0	$ (2.88)
Diluted (in dollars per share)	$ 0	$ 0	$ (2.88)
Weighted-average limited partner units outstanding:
Basic (shares)	0	0	24,410
Diluted (shares)	0	0	24,410