EQUITY METHOD INVESTMENTS - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		11 Months Ended		12 Months Ended
	May 31, 2014	Jan. 31, 2014	Nov. 30, 2017	Nov. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Acquisition of initial interest in Ohio Gathering					$ 25,513	$ 31,582	$ 86,200
OGC
Schedule Of Equity Method Investments [Line Items]
Non-affiliated owners' interest percent	60.00%
OGC | Principal Owner
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest					40.00%
Equity Method Investment [Roll Forward]
Asset impairment					$ 1,400
OGC | Summit Midstream Partners, LLC
Schedule Of Equity Method Investments [Line Items]
Cost method ownership interest		1.00%
Ownership interest value		$ 190,000
Capital contribution		$ 8,400
Equity method potential ownership interest		40.00%
Percentage of ownership interest	40.00%
Capital contributions true-ups	$ 326,600
Acquisition of initial interest in Ohio Gathering	50,400
Management fee	$ 5,400
Option value		$ 7,500
Equity Method Investment [Roll Forward]
Asset impairment			$ 1,383	$ 0