Note 12 - Business Segments, Sales of Products and Significant Customers - Sales of Products (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales of products	$ 691,873	$ 673,266	$ 567,137
Less: Smelter and refining charges	(68,361)	(33,004)	(24,177)
Sales by significant product type	708,253	674,549	559,053
Silver Contracts [Member]
Sales of products	260,227	192,235	144,609
Doré and Metals from Doré [Member]
Sales by significant product type	266,536	340,912	306,328
Gold [Member]
Sales of products	356,166	388,602	313,076
Carbon [Member]
Sales by significant product type	60,302	37,645	5,239
Lead [Member]
Sales of products	48,776	35,777	33,829
Lead Concentrate [Member]
Sales by significant product type	281,050	200,456	148,880
Zinc [Member]
Sales of products	95,065	89,656	99,800
Zinc Concentrate [Member]
Sales by significant product type	76,481	74,160	80,938
Bulk Concentrate [Member]
Sales by significant product type	$ 23,884	$ 21,376	$ 17,668