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Inventories (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Inventory Disclosure [Abstract]    
Coal - NACoal $ 13,137 $ 16,652
Mining supplies - NACoal 15,790 21,755
Total inventories at weighted average cost 28,927 38,407
Sourced inventories - HBB 95,008 97,511
Retail inventories - KC 33,407 29,098
Total inventories $ 157,342 $ 165,016