CONSOLIDATED BALANCE SHEETS (Parenthetical) (Cloud Peak Energy Inc. and Subsidiaries) (USD $)	Dec. 31, 2011	Dec. 31, 2010
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	60,923	60,878
Common stock, shares outstanding	60,923	60,878

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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