Note 6 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Sales of products	$ 134,172	$ 147,259	$ 286,789	$ 286,968
Less: Smelter and refining charges	(9,910)	(7,105)	(16,258)	(14,998)
Sales by significant product type	132,879	144,563	287,972	283,657
Silver Contracts [Member]
Sales of products	36,298	38,425	81,804	73,647
Doré and Metals from Doré [Member]
Sales by significant product type	77,596	75,526	153,497	149,018
Gold [Member]
Sales of products	78,166	77,635	157,845	150,679
Lead Concentrate [Member]
Sales by significant product type	35,742	42,149	85,042	76,483
Lead [Member]
Sales of products	6,670	10,690	15,695	19,917
Zinc Concentrate [Member]
Sales by significant product type	15,738	22,579	39,530	48,231
Zinc [Member]
Sales of products	22,948	27,614	47,703	57,723
Bulk Concentrate [Member]
Sales by significant product type	$ 3,803	$ 4,309	$ 9,903	$ 9,925