Note 11. Derivative Instruments (Detail) - Summary Of Forward Sales Contracts (USD $)	6 Months Ended
	Jun. 30, 2011
Zinc [Member] | Settlements2011 [Member]
Contracts on provisional sales
2011 settlements	8,100
Zinc [Member] | Settlements2011 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	7,350
Zinc [Member] | Settlements2012 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	26,650
Zinc [Member] | Settlements2013 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	4,700
Zinc [Member] | Settlements2011 [Member]
Contracts on provisional sales
2011 settlements	$ 1.02
Zinc [Member] | Settlements2011 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	0.96
Zinc [Member] | Settlements2012 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	1.11
Zinc [Member] | Settlements2013 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	1.16
Lead [Member] | Settlements2011 [Member]
Contracts on provisional sales
2011 settlements	4,500
Lead [Member] | Settlements2011 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	6,175
Lead [Member] | Settlements2012 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	18,000
Lead [Member] | Settlements2013 [Member]
Contracts on forecasted sales
Metric tonnes under contract - forecasted sales	8,300
Lead [Member] | Settlements2011 [Member]
Contracts on provisional sales
2011 settlements	1.17
Lead [Member] | Settlements2011 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	1.01
Lead [Member] | Settlements2012 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	1.11
Lead [Member] | Settlements2013 [Member]
Contracts on forecasted sales
Average price per pound - forecasted sales	$ 1.16