Note 4 - Business Segments, Sales of Products and Significant Customers - Sales of Products (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net sales	$ 807,473	$ 691,873	$ 673,266
Less: Smelter and refining charges	(48,933)	(68,361)	(33,004)
Silver Contracts [Member]
Net sales	293,646	260,227	192,235
Gold [Member]
Net sales	362,037	356,166	388,602
Lead [Member]
Net sales	75,431	48,776	35,777
Zinc [Member]
Net sales	$ 125,292	$ 95,065	$ 89,656