Impairment Charges Impairment Charges (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment and mine closure costs	$ 200,397,000	$ (2,144,000)	$ 220,879,000	$ 523,439,000
Impaired Long-Lived Assets Held and Used, Asset Name [Domain]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment and mine closure costs			142,800,000
Assets, Fair Value Disclosure, Nonrecurring	$ 71,300,000		$ 71,300,000