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, 2015	Dec. 31, 2014	Dec. 31, 2013
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	22.50%	25.80%	25.00%
Korea Zinc [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	16.00%	14.10%	22.50%
CIBC [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	17.60%	17.00%	10.90%
Mitsui [Member] | Sales Revenue, Goods, Net [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Significant metal customers	10.20%	15.80%	8.40%