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Reclamation and Mine Closure (Details) (USD $)	3 Months Ended		9 Months Ended
Reclamation and Mine Closure (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Entity Information [Line Items]
Addition and changes in estimates	$ 19,542,000	$ 0	$ 19,542,000	$ 335,000
Asset retirement obligation - Beginning	35,578,000	34,510,000	34,456,000	32,714,000
Accretion	777,000	714,000	2,277,000	2,180,000
Settlements	(124,000)	(13,000)	(502,000)	(18,000)
Asset retirement obligation - March 31	55,773,000	35,211,000	55,773,000	35,211,000
Reclamation and Mine Closure (Textual) [Abstract]
Accrued reclamation liabilities	600,000		600,000		900,000
Rochester [Member]
Entity Information [Line Items]
Addition and changes in estimates	16,800,000
Kensington [Member]
Entity Information [Line Items]
Addition and changes in estimates	$ 2,700,000

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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