RELATED PARTY TRANSACTIONS - Schedule of Related Party Disclosures (Details) - Majority Shareholder - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 2,741	$ 2,714	$ 6,560	$ 5,045
Operating and Other Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	767	761	1,530	1,447
Selling, General and Administrative Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 1,974	$ 1,953	$ 5,030	$ 3,598