Note 12 - Business Segments, Sales of Products and Significant Customers - Sales of Products (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sales of products	$ 567,137	$ 577,775	$ 645,957
Less: Smelter and refining charges	(24,177)	(36,477)	(64,111)
Sales by significant product type	559,053	583,758	660,193
Silver [Member]
Sales of products	144,609	194,813	274,438
Doré and Metals from Doré [Member]
Sales by significant product type	311,567	295,176	313,784
Gold [Member]
Sales of products	313,076	277,421	276,630
Lead Concentrate [Member]
Sales by significant product type	148,880	179,143	250,153
Lead [Member]
Sales of products	33,829	37,995	63,942
Zinc Concentrate [Member]
Sales by significant product type	80,938	88,688	82,872
Zinc [Member]
Sales of products	99,800	104,023	95,058
Bulk Concentrate [Member]
Sales by significant product type	$ 17,668	$ 20,751	$ 13,384