Note 11- 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, 2019	Dec. 31, 2018	Dec. 31, 2017
Teck Metals Ltd [Member]
Significant metal customers	8.20%	8.40%	11.30%
Korea Zinc [Member]
Significant metal customers	17.40%	17.80%	16.40%
Scotia [Member]
Significant metal customers	24.00%	15.30%	24.90%
CIBC [Member]
Significant metal customers	23.10%	29.70%	22.80%