RELATED PARTY TRANSACTIONS - Schedule of Related Party Disclosures (Details) - Majority Shareholder - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 2,714	$ 1,604	$ 5,045	$ 3,193
Operating and Other Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	761	867	1,447	1,739
Selling, General and Administrative Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 1,953	$ 737	$ 3,598	$ 1,454