Note 6 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Sales of products	$ 136,925	$ 152,617
Less: Smelter and refining charges	(15,069)	(6,348)
Sales by significant product type	135,245	155,093
Silver Contracts [Member]
Sales of products	37,572	45,506
Doré and Metals from Doré [Member]
Sales by significant product type	67,327	75,449
Gold [Member]
Sales of products	90,694	79,679
Carbon [Member]
Sales by significant product type	19,368	452
Lead [Member]
Sales of products	6,420	9,025
Lead Concentrate [Member]
Sales by significant product type	34,154	49,300
Zinc [Member]
Sales of products	17,308	24,755
Zinc Concentrate [Member]
Sales by significant product type	10,820	23,792
Bulk Concentrate [Member]
Sales by significant product type	$ 3,576	$ 6,100