Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Inventories
Materials and supplies	$ 77,399	$ 77,736
Less: Obsolescence allowance	(1,101)	(1,102)
Material and supplies, net	76,298	76,634
Coal inventory	2,415	3,168
Inventories, net	$ 78,714	$ 79,802