Note 3 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Sales of products	$ 193,560	$ 199,703	$ 622,395	$ 502,983
Less: Smelter and refining charges	(11,669)	(18,587)	(38,189)	(52,177)
Silver Contracts [Member]
Sales of products	61,890	79,684	232,414	179,013
Gold [Member]
Sales of products	94,984	98,457	282,471	278,363
Lead [Member]
Sales of products	18,082	13,370	56,198	32,244
Zinc [Member]
Sales of products	$ 30,273	$ 26,779	$ 89,501	$ 65,540