Note 10. Derivative Instruments (Detail) - Summary Of Forward Sales Contracts (USD $)	12 Months Ended
	Dec. 31, 2011 MT	Dec. 31, 2010 MT
2012 Settlements [Member] | Zinc [Member]
Contracts on provisional sales
Metric Tonnes Under Contract	9,600
Average Price Per Pound	$ 0.86
Contracts on forecasted sales
Metric Tonnes Under Contract	20,500	21,475
Average Price Per Pound	1.12	1.11
2012 Settlements [Member] | Lead [Member]
Contracts on provisional sales
Metric Tonnes Under Contract	2,600
Average Price Per Pound	0.89
Contracts on forecasted sales
Metric Tonnes Under Contract	15,900	15,000
Average Price Per Pound	1.12	1.11
2013 Settlements [Member] | Zinc [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	8,275
Average Price Per Pound	1.14
2013 Settlements [Member] | Lead [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	11,150
Average Price Per Pound	1.17
2011 Settlements [Member] | Zinc [Member]
Contracts on provisional sales
Metric Tonnes Under Contract		11,575
Average Price Per Pound		1.05
Contracts on forecasted sales
Metric Tonnes Under Contract		19,475
Average Price Per Pound		0.96
2011 Settlements [Member] | Lead [Member]
Contracts on provisional sales
Metric Tonnes Under Contract		3,925
Average Price Per Pound		1.11
Contracts on forecasted sales
Metric Tonnes Under Contract		15,550
Average Price Per Pound		$ 0.96