Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Coal	$ 119,785	$ 71,901
Repair parts and supplies	119,250	118,352
Inventories	239,035	190,253
Allowance for slow-moving and obsolete inventories	$ 6,700	$ 6,600

Amount of valuation reserve for inventory.

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