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Related Party Transactions (Details) (Venture Fuels Partnership, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Related Party Transactions
Equity investment in Venture Fuels Partnership (as a percent)	50.00%
Coal sales
Related Party Transactions
Revenue	$ 171	$ 1,187

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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