UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Total revenues	$ 131,408	$ 117,320
Costs and expenses:
Cost of natural gas and NGLs	$ 31,759	$ 20,286
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasPurchasedMember	us-gaap:OilAndGasPurchasedMember
Operation and maintenance	$ 24,222	$ 24,604
General and administrative	17,281	14,385
Depreciation and amortization	27,727	26,677
Transaction costs	950	57
Gain on asset sales, net	(961)	(74)
Long-lived asset impairment	44,951	0
Total costs and expenses	145,929	85,935
Other income (expense), net	209	(7)
Interest expense	(17,527)	(15,122)
Deferred Purchase Price Obligation	(4,427)	(21,658)
Loss before income taxes and (loss) income from equity method investees	(36,266)	(5,402)
Income tax (expense) benefit	(207)	171
(Loss) income from equity method investees	(441)	1,386
Net loss	(36,914)	(3,845)
Net income attributable to noncontrolling interest	0	85
Net loss attributable to SMLP	(36,914)	(3,930)
Net income attributable to General Partner, including IDRs	12	2,058
Net loss attributable to limited partners	(36,926)	(5,988)
Series A Preferred Units
Costs and expenses:
Net loss attributable to limited partners	7,125	7,125
Common units
Costs and expenses:
Net loss attributable to limited partners	$ (44,051)	$ (13,113)
Loss per limited partner unit:
Basic (in dollars per share)	$ (0.58)	$ (0.18)
Diluted (in dollars per share)	$ (0.58)	$ (0.18)
Weighted-average limited partner units outstanding:
Basic (shares)	75,793	73,134
Diluted (shares)	75,793	73,134
Gathering Services and Related Fees
Revenues:
Total revenues	$ 86,964	$ 84,361
Natural Gas, NGLs and Condensate Sales
Revenues:
Total revenues	37,928	26,117
Other Revenues
Revenues:
Total revenues	$ 6,516	$ 6,842