Inventories (Inventories) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]
Coal	$ 134,481,000	$ 180,917,000
Repair parts and supplies	143,763,000	172,139,000
Work-in-process	9,165,000	12,368,000
Inventories	287,409,000	365,424,000
Allowance for slow-moving and obsolete inventories	$ 8,800,000	$ 13,600,000

Carrying amount as of the balance sheet date of coal, which is a combustible rock or minerals which are extracted from the ground and used as fuel.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date for elements of machinery or equipment held for the purpose of replacing similar parts in the course of repair or maintenance.

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Amount of valuation reserve for inventory.

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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

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