DEBT - Components of Long-Term Debt (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Long-term debt		$ 1,304,918	$ 1,347,326
Summit Midstream Partners Holdings L L C
Line of Credit Facility [Line Items]
Total debt		1,304,918	1,347,326
Less: current portion		0	0
Long-term debt		1,304,918	1,347,326
Summit Midstream Partners Holdings L L C | Senior Secured Revolving Credit Facility Due May 2022
Line of Credit Facility [Line Items]
Revolving credit facility		802,000	857,000
Summit Midstream Partners Holdings L L C | Permian Transmission Credit Facility [Member]
Line of Credit Facility [Line Items]
Secured notes		17,500	0
Less unamortized debt issuance costs	[1]	(5,105)	0
Summit Midstream Partners Holdings L L C | Senior Notes Due August 2022
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	[1]	(725)	(859)
Unsecured notes		234,047	234,047
Summit Midstream Partners Holdings L L C | Senior Notes Due April 2025
Line of Credit Facility [Line Items]
Less unamortized debt issuance costs	[1]	(2,262)	(2,325)
Unsecured notes		$ 259,463	$ 259,463

[1] Issuance costs are being amortized over the life of the notes.