Note 6 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Sales of products	$ 166,355	$ 134,172	$ 303,280	$ 286,789
Less: Smelter and refining charges	(18,522)	(9,910)	(33,590)	(16,258)
Sales by significant product type	171,353	132,879	306,598	287,972
Silver Contracts [Member]
Sales of products	61,756	36,298	99,328	81,804
Doré and Metals from Doré [Member]
Sales by significant product type	59,445	73,312	143,780	144,167
Gold [Member]
Sales of products	89,212	78,166	179,906	157,845
Carbon [Member]
Sales by significant product type	16,903	4,284	19,264	9,330
Lead [Member]
Sales of products	12,454	6,670	18,874	15,695
Lead Concentrate [Member]
Sales by significant product type	72,514	35,742	106,667	85,042
Zinc [Member]
Sales of products	21,455	22,948	38,762	47,703
Zinc Concentrate [Member]
Sales by significant product type	16,585	15,738	27,405	39,530
Bulk Concentrate [Member]
Sales by significant product type	$ 5,906	$ 3,803	$ 9,482	$ 9,903