Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Inventory Disclosure [Abstract]
Coal - NACoal	$ 20,565	$ 29,576	$ 25,749
Mining supplies - NACoal	21,083	19,774	18,641
Total inventories at weighted average cost	41,648	49,350	44,390
Sourced inventories - HBB	151,663	104,746	130,012
Retail inventories - KC	40,903	36,286	46,205
Total inventories at FIFO	192,566	141,032	176,217
Inventories, net	$ 234,214	$ 190,382	$ 220,607