Note 11. Derivative Instruments (Detail) - Summary Of Forward Sales Contracts (USD $)	9 Months Ended
	Sep. 30, 2011
Settlements 2011 [Member] | Zinc [Member]
Contracts on provisional sales
2011 settlements (in Dollars)	$ 1.03
Settlements 2011 [Member] | Lead [Member]
Contracts on provisional sales
2011 settlements (in Dollars)	1.00
Settlements 2011 [Member] | Zinc [Member]
Contracts on provisional sales
2011 settlements	5,125
Settlements 2011 [Member] | Lead [Member]
Contracts on provisional sales
2011 settlements	2,800
Settlements 2011 [Member] | Zinc [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	0.99
Settlements 2011 [Member] | Lead [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	1.05
Settlements 2011 [Member] | Zinc [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	2,300
Settlements 2011 [Member] | Lead [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	2,275
Settlements 2012 [Member] | Zinc [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	1.11
Settlements 2012 [Member] | Lead [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	1.11
Settlements 2012 [Member] | Zinc [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	26,650
Settlements 2012 [Member] | Lead [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	18,000
Settlements 2013 [Member] | Zinc [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	1.14
Settlements 2013 [Member] | Lead [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales (in Dollars)	$ 1.17
Settlements 2013 [Member] | Zinc [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	8,275
Settlements 2013 [Member] | Lead [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	11,150