Note 10. Derivative Instruments (Detail) (USD $)	0 Months Ended		1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Jun. 29, 2009	Jun. 08, 2009	Feb. 03, 2009	Mar. 01, 2012	Sep. 30, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Assets, Current						$ 17,700,000
Derivative, Gain on Derivative						38,000,000
Derivative Assets, Noncurrent						14,700,000
Derivative Liability, Fair Value, Net						700,000
Derivative, Loss on Derivative					38,000	(37,988,000)	20,758,000
Payments for (Proceeds from) Derivative Instrument, Financing Activities				3,100,000
Debt Instrument, Annual Principal Payment						66,700,000
Line of Credit Facility, Decrease, Repayments	18,200,000	57,100,000
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net			200,000
Derivative, Net Hedge Ineffectiveness Gain (Loss)								2.7
Forecasted Future Concentrate Contracts [Member]
Derivative Assets, Current						300,000
Unsettled Concentrate Sales Contracts [Member]
Derivative, Gain on Derivative						7,200,000
Losses Realized On Settled Contracts [Member]
Derivative, Loss on Derivative						$ 13,400,000