RELATED PARTY TRANSACTIONS - Schedule of Related Party Disclosures (Details) - Majority Shareholder - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 3,070	$ 1,684	$ 8,115	$ 4,877
Operating and Other Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	725	850	2,172	2,589
Selling, General and Administrative Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 2,345	$ 834	$ 5,943	$ 2,288