Note 6 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Sales of products	$ 139,709	$ 142,544
Less: Smelter and refining charges	(7,893)	(14,998)
Sales by significant product type	139,094	146,637
Silver [Member]
Sales of products	35,222	51,357
Doré and Metals from Doré [Member]
Sales by significant product type	73,492	68,981
Gold [Member]
Sales of products	73,044	62,701
Lead Concentrate [Member]
Sales by significant product type	34,334	48,917
Lead [Member]
Sales of products	9,227	13,619
Zinc Concentrate [Member]
Sales by significant product type	25,652	24,218
Zinc [Member]
Sales of products	30,109	29,865
Bulk Concentrate [Member]
Sales by significant product type	$ 5,616	$ 4,521