Note 7 - Business Segments and Sales of Products - Sales of Products (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Sales of products	$ 143,649	$ 140,839	$ 430,617	$ 417,662
Less: Smelter and refining charges	(5,530)	(6,692)	(20,530)	(29,064)
Sales by significant product type	138,627	141,465	422,284	421,574
Silver [Member]
Sales of products	38,009	43,228	111,656	140,662
Doré and Metals from Doré [Member]
Sales by significant product type	83,068	82,764	232,085	219,276
Gold [Member]
Sales of products	82,628	73,603	233,308	203,279
Lead Concentrate [Member]
Sales by significant product type	36,728	31,548	113,211	124,553
Lead [Member]
Sales of products	7,552	6,373	27,469	28,093
Zinc Concentrate [Member]
Sales by significant product type	14,965	21,278	63,197	61,841
Zinc [Member]
Sales of products	20,990	24,327	78,714	74,692
Bulk Concentrate [Member]
Sales by significant product type	$ 3,866	$ 5,875	$ 13,791	$ 15,904