UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 8,988	$ 3,762
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	28,746	29,900
Noncash lease expense	289	473
Amortization of debt issuance costs	1,717	1,582
Unit-based and noncash compensation	1,967	2,723
Income from equity method investees	(2,315)	(3,311)
Distributions from equity method investees	6,268	7,494
(Gain) loss on asset sales, net	(136)	115
Loss on ECP Warrants and other	1,481	0
Long-lived asset impairment	1,492	3,821
Changes in operating assets and liabilities:
Accounts receivable	7,592	18,470
Trade accounts payable	4,544	3,973
Accrued expenses	(1,546)	(138)
Deferred revenue, net	(576)	5,161
Ad valorem taxes payable	(1,497)	(4,781)
Accrued interest	504	3,059
Accrued environmental remediation, net	324	(17)
Other, net	(6,412)	(2,085)
Net cash provided by operating activities	51,430	70,201
Cash flows from investing activities:
Capital expenditures	(2,610)	(18,583)
Proceeds from asset sale	8,000	0
Other, net	0	217
Net cash used in investing activities	(229)	(76,399)
Cash flows from financing activities:
Net cash distributions to noncontrolling interest SMLP unitholders	0	(6,037)
Borrowings under Revolving Credit Facility	0	55,000
Repayments on Revolving Credit Facility	(55,000)	(34,000)
Repayments on SMPH Term Loan before TL Restructuring	0	(750)
Proceeds from issuance of Subsidiary Series A preferred units, net of issuance costs	0	33,946
Debt issuance costs	(4,909)	(101)
Proceeds from asset sale	143	0
Other, net	(179)	(1,401)
Net cash provided by (used in) financing activities	(42,445)	46,657
Net change in cash, cash equivalents and restricted cash	8,756	40,459
Cash, cash equivalents and restricted cash, beginning of period	15,544	36,922
Cash, cash equivalents and restricted cash, end of period	24,300	77,381
Permian Transmission Credit Facility [Member]
Cash flows from financing activities:
Borrowings under Revolving Credit Facility	17,500	0
Double E
Cash flows from investing activities:
Investment in Double E equity method investee	$ (5,619)	$ (58,033)