Note 11. Derivative Instruments (Detail) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Derivative, Loss on Derivative	$ 5,231,000	$ 2,034,000
Derivative Assets, Noncurrent	9,000,000
Derivative, Gain on Derivative	7,000,000
Payments for (Proceeds from) Derivative Instrument, Financing Activities	3,100,000
Concentrate Shipments Between Time of Sale and Settlement [Member]
Derivative Assets, Current	500,000
Derivative Liability, Fair Value, Net	100,000
Derivative, Loss on Derivative	1,000,000
Forecasted Future Concentrate Shipments [Member]
Derivative Assets, Current	11,100,000
Derivative Liability, Fair Value, Net	$ 500,000