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Reclamation and Mine Closure (Details) (USD $)	3 Months Ended		9 Months Ended
Reclamation and Mine Closure (Details) (USD $)	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Asset retirement obligation
Asset retirement obligation - Beginning			$ 32,714,000	$ 27,302,000	$ 34,510,000		$ 28,557,000
Accretion	714,000	670,000	2,180,000	1,961,000
Addition and changes in estimates	0	0	335,000	0
Settlements	(13,000)	(15,000)	(18,000)	(51,000)
Asset retirement obligation - March 31	35,211,000	29,212,000	35,211,000	29,212,000	34,510,000		28,557,000
Reclamation and Mine Closure (Textual) [Abstract]
Accrued reclamation liabilities	$ 800,000		$ 800,000			$ 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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