INVENTORIES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
INVENTORIES
Coal	$ 83,682	$ 50,130
Supplies (net of reserve for obsolescence of $3,841 and $2,935, respectively)	37,399	33,025
Total inventory	121,081	83,155
Reserve for obsolescence	$ 3,841	$ 2,935