Note 6 - Business Segments and Sales of Products - Sales From Continuing Operations to Significant Metals Customers As a Percentage of Total Sales (Details) - Sales Revenue, Goods, Net [Member] - Customer Concentration Risk [Member]	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CIBC [Member]
Significant metal customers	47.00%	24.00%
Scotia [Member]
Significant metal customers	2.00%	20.00%
Korea Zinc [Member]
Significant metal customers	23.00%	20.00%
Teck Metals Ltd [Member]
Significant metal customers	4.00%	15.00%
Ocean Partners [Member]
Significant metal customers	10.00%	10.00%