Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Inventories
Materials and supplies	$ 74,050	$ 77,736
Less: Obsolescence allowance	(1,050)	(1,102)
Material and supplies, net	73,000	76,634
Coal inventory	2,503	3,168
Inventories, net	$ 75,503	$ 79,802