Inventories (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Inventory Disclosure [Abstract]
Coal - NACoal	$ 29,521	$ 24,710	$ 14,685
Mining supplies - NACoal	17,920	17,406	15,299
Total inventories at weighted average cost	47,441	42,116	29,984
Sourced inventories - HBB	97,322	90,713	80,007
Retail inventories - KC	49,150	51,616	52,243
Total inventories at FIFO	146,472	142,329	132,250
Inventories, net	$ 193,913	$ 184,445	$ 162,234