Note 10 - Derivative Instruments (Detail) - Summary Of Forward Sales Contracts (USD $)	12 Months Ended
	Dec. 31, 2012 oz	Dec. 31, 2011 oz
Zinc [Member] | 2013 Settlements [Member]
Contracts on provisional sales
Metric Tonnes Under Contract	14,991
Average Price Per Pound (in Dollars)	$ 0.95
Contracts on forecasted sales
Metric Tonnes Under Contract	35,935	18,243
Average Price Per Pound (in Dollars)	0.96	1.14
Zinc [Member] | 2014 Settlements [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	30,203
Average Price Per Pound (in Dollars)	0.98
Zinc [Member] | 2015 Settlements [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	3,307
Average Price Per Pound (in Dollars)	1.01
Zinc [Member] | 2012 Settlements [Member]
Contracts on provisional sales
Metric Tonnes Under Contract		21,164
Average Price Per Pound (in Dollars)		0.86
Contracts on forecasted sales
Metric Tonnes Under Contract		45,195
Average Price Per Pound (in Dollars)		1.12
Lead [Member] | 2013 Settlements [Member]
Contracts on provisional sales
Metric Tonnes Under Contract	6,945
Average Price Per Pound (in Dollars)	1.00
Contracts on forecasted sales
Metric Tonnes Under Contract	32,794	24,582
Average Price Per Pound (in Dollars)	1.11	1.17
Lead [Member] | 2014 Settlements [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	33,069
Average Price Per Pound (in Dollars)	1.03
Lead [Member] | 2015 Settlements [Member]
Contracts on forecasted sales
Metric Tonnes Under Contract	23,534
Average Price Per Pound (in Dollars)	1.06
Lead [Member] | 2012 Settlements [Member]
Contracts on provisional sales
Metric Tonnes Under Contract		5,732
Average Price Per Pound (in Dollars)		0.89
Contracts on forecasted sales
Metric Tonnes Under Contract		35,053
Average Price Per Pound (in Dollars)		$ 1.12