Mine Closure and Asset Impairment Costs (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2012 mining_complex
Restructuring and Related Activities [Abstract]
number of mining complexes temporarily idled		1
number of mining complexes closed		4
Long-Lived Assets to be Abandoned, Carrying Value of Asset	$ 51,000,000	$ 51,000,000
Curtailments	$ (2,200,000)	$ (1,770,000)
Restructuring and Related Cost, Number of Positions Eliminated		750

The amount of decrease that is related to an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.

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+ Details