Note 12- Business Segments, Sales of Products and Significant Customers - Sales from Continuing Operations to Significant Metals Customers As a Percentage of Total Sales (Details) - Customer Concentration Risk [Member] - Revenue from Contract with Customer Benchmark [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CIBC [Member]
Significant metal customers	32.70%	23.10%	29.70%
Teck Metals Ltd [Member]
Significant metal customers	16.10%	8.20%	8.40%
Ocean Partners [Member]
Significant metal customers	13.90%	5.70%	2.50%
Korea Zinc [Member]
Significant metal customers	13.30%	17.40%	17.80%
Scotia [Member]
Significant metal customers	2.90%	24.00%	15.30%