Note 11 - Derivative Instruments (Detail) - Summary Of Forward Sales Contracts (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013 lb	Dec. 31, 2012 lb
Zinc [Member] | 2013 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract	14,716,000	14,991,000
Average Price Per Pound (in Dollars)	$ 0.93	$ 0.95
Contracts on forecasted sales
Pounds Under Contract	30,258,000	35,935,000
Average Price Per Pound (in Dollars)	0.98	0.96
Zinc [Member] | 2014 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract	60,516,000	30,203,000
Average Price Per Pound (in Dollars)	0.99	0.98
Zinc [Member] | 2015 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract	20,944,000	3,307,000
Average Price Per Pound (in Dollars)	1.00	1.01
Lead [Member] | 2013 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract	7,165,000	6,945,000
Average Price Per Pound (in Dollars)	1.08	1.00
Contracts on forecasted sales
Pounds Under Contract	26,951,000	32,794,000
Average Price Per Pound (in Dollars)	1.09	1.11
Lead [Member] | 2014 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract	47,619,000	33,069,000
Average Price Per Pound (in Dollars)	1.05	1.03
Lead [Member] | 2015 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract	37,864,000	23,534,000
Average Price Per Pound (in Dollars)	$ 1.07	$ 1.06