INVENTORIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
INVENTORIES
Coal	$ 83,682		$ 29,242
Supplies (net of reserve for obsolescence of $4,940 and $3,841, respectively)	37,399		31,809
Total inventories, net	121,081		61,051
Reserve for obsolescence	3,841		$ 4,940
Adjustment to reduce carrying value of coal inventories to market	$ 1,952	$ 377