Note 6 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Sales of products	$ 147,259	$ 134,279	$ 286,968	$ 276,823
Less: Smelter and refining charges	(7,105)	(7,374)	(14,998)	(22,372)
Sales by significant product type	144,563	133,472	283,657	280,108
Silver [Member]
Sales of products	38,425	46,077	73,647	97,434
Doré and Metals from Doré [Member]
Sales by significant product type	75,526	67,533	149,018	136,513
Gold [Member]
Sales of products	77,635	66,975	150,679	129,676
Lead Concentrate [Member]
Sales by significant product type	42,149	44,087	76,483	93,004
Lead [Member]
Sales of products	10,690	8,101	19,917	21,720
Zinc Concentrate [Member]
Sales by significant product type	22,579	16,344	48,231	40,562
Zinc [Member]
Sales of products	27,614	20,500	57,723	50,365
Bulk Concentrate [Member]
Sales by significant product type	$ 4,309	$ 5,508	$ 9,925	$ 10,029