MISCELLANEOUS OTHER INCOME (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Income and Expenses [Abstract]
Royalty Income - Non-Operated Coal	$ 6,210	$ 9,806
Purchased Coal Sales	3,186	8,746
Property Easements and Option Income	979	4,151
Interest Income	887	601
Rental Income	617	1,122
Other	1,413	1,461
Miscellaneous Other Income	$ 13,292	$ 25,887