Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Inventory Disclosure [Abstract]
Coal - NACoal	$ 13,155	$ 13,137	$ 16,305
Mining supplies - NACoal	16,100	15,790	20,810
Total inventories at weighted average cost	29,255	28,927	37,115
Sourced inventories - HBB	98,688	95,008	94,482
Retail inventories - KC	31,039	33,407	32,737
Total inventories	$ 158,982	$ 157,342	$ 164,334