ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 28, 2020	Mar. 31, 2021	Dec. 31, 2020	Nov. 17, 2020
Organization And Business Operations [Line Items]
Purchase agreement date		May 28, 2020
Common limited partner capital (shares)		6,206,021	6,110,092
Common Units
Organization And Business Operations [Line Items]
Number of common units purchased.	537,307
Common Units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (shares)		400,000
Summit Midstream Partners Holdings L L C
Organization And Business Operations [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan		2,300,000
Common Units Not Pledged As Collateral		700,000		34,600,000
Common units issued prior to reverse unit split		10,700,000
Common units retire		1,100,000
Summit Investments
Organization And Business Operations [Line Items]
Cash paid to Acquire investment		$ 35.0
Summit Investments | Common Units
Organization And Business Operations [Line Items]
Common units issued prior to reverse unit split		10,000,000.0
Number of common units purchased.		700,000
SMP Holdings
Organization And Business Operations [Line Items]
Debt discharge and restructuring		$ 155.2