Note 11 - Business Segments and Significant Customers (Details) - Sales from Continuing Operations to Significant Metals Customers as a Percentage of Total Sales	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue, Major Customer [Line Items]
Significant metal customers	100.00%	100.00%	100.00%
Teck Metals Ltd. [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	25.80%	25.00%	10.70%
Korea Zinc [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	14.10%	22.50%	37.20%
Trafigura AG [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	7.00%	8.80%	22.40%
MS Zinc [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	5.90%	7.50%	12.30%
CIBC [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	17.00%	10.90%
Mitsui [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	15.80%	8.40%