Note 7 - 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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
CIBC [Member]
Significant metal customers	26.00%	23.00%	34.00%	24.00%
Scotia [Member]
Significant metal customers	19.00%	33.00%	13.00%	26.00%
Korea Zinc [Member]
Significant metal customers	15.00%	25.00%	22.00%	20.00%
Teck Metals Ltd [Member]
Significant metal customers	11.00%		11.00%	10.00%
Trafigura AG [Member]
Significant metal customers	10.00%		3.00%	4.00%
Louis Dreyfus [Member]
Significant metal customers		12.00%		4.00%