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Reclamation and Mine Closure (Details) (USD $)	3 Months Ended
Reclamation and Mine Closure (Details) (USD $)	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Asset retirement obligation
Asset retirement obligation - Beginning	$ 32,714,000	$ 27,302,000
Accretion	724,000	637,000
Addition and changes in estimates	0	0
Settlements	(4,000)	(31,000)
Asset retirement obligation - March 31	33,434,000	27,908,000
Reclamation and Mine Closure (Textual) [Abstract]
Accrued reclamation liabilities	$ 1,000,000		$ 1,000,000

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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