MISCELLANEOUS OTHER INCOME (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Income and Expenses [Abstract]
Royalty Income - Non-Operated Coal	$ 5,677	$ 4,142	$ 11,887	$ 13,948
Purchased Coal Sales	2,730	3,742	5,916	12,488
Contract Buyout	1,342	350	2,390	350
Interest Income	757	467	1,644	1,068
Rental Income	681	1,048	1,298	2,170
Property Easements and Option Income	450	259	1,429	4,410
Other	557	361	922	1,822
Miscellaneous Other Income	$ 12,194	$ 10,369	$ 25,486	$ 36,256