CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (Cloud Peak Energy Inc. and Subsidiaries) (USD $)	Mar. 31, 2013	Dec. 31, 2012
CONDENSED CONSOLIDATED BALANCE SHEETS
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000	200,000
Common stock, shares issued	61,113	61,114
Common stock, shares outstanding	60,822	60,839
Treasury stock, shares	291	276

Face amount or stated value of common stock per share; generally not indicative of the fair market value per share.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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