RELATED PARTY TRANSACTIONS - Schedule of Related Party Transactions (Details) - CONSOL Energy - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 1,684	$ 1,710	$ 4,877	$ 6,480
Operating and Other Costs
Related Party Transaction [Line Items]
Expenses from transactions with related party	850	854	2,589	3,390
Selling, General and Administrative Expenses
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 834	$ 856	$ 2,288	$ 3,090