EQUITY METHOD INVESTMENTS - Rollforward of the Investment in Equity Method Investees (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, March 31,	$ 394,405	$ 394,405
March cash distributions		6,268	$ 7,494
Investment in Ohio Gathering (Books and records), February 28,		392,740
OGC | Summit Midstream Partners, LLC
Schedule Of Equity Method Investments [Line Items]
Investment in Ohio Gathering, March 31,	256,430	$ 256,430
March cash distributions	2,196
Basis difference	214,426
Investment in Ohio Gathering (Books and records), February 28,	$ 473,052