Note 2 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Sales of products	$ 217,983	$ 166,355	$ 428,835	$ 303,280
Less: Smelter and refining charges	(13,120)	(18,522)	(26,521)	(33,590)
Silver Contracts [Member]
Sales of products	92,765	61,756	170,525	99,328
Gold [Member]
Sales of products	86,078	89,212	187,487	179,906
Lead [Member]
Sales of products	22,223	12,454	38,116	18,874
Zinc [Member]
Sales of products	$ 30,037	$ 21,455	$ 59,228	$ 38,762