ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	May 28, 2020	Sep. 30, 2020	Dec. 31, 2019
Organization And Business Operations [Line Items]
Purchase agreement date		May 28, 2020
Common limited partner capital (shares)		56,624,887	45,318,866
Common Units
Organization And Business Operations [Line Items]
Number of common units purchased.	8,059,609
Common Units | Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (shares)		5,915,827
Summit Midstream Partners Holdings L L C
Organization And Business Operations [Line Items]
SMLP common units pledged as collateral under the SMPH Term Loan		34,604,581
SMLP common units not pledged as collateral under the SMPH Term Loan		10,714,285
Common units retire		16,630,112
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]
Number of common units purchased.		10,000,000