Note 6 - Business Segments and Sales of Products - Sales by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Sales by geographical area	$ 155,093	$ 139,094
Sales by significant product type	155,093	139,094
Doré and Metals from Doré [Member]
Sales by geographical area	75,901	73,492
Sales by significant product type	75,901	73,492
Lead Concentrate [Member]
Sales by geographical area	49,300	34,334
Sales by significant product type	49,300	34,334
Zinc Concentrate [Member]
Sales by geographical area	23,792	25,652
Sales by significant product type	23,792	25,652
Bulk Concentrate [Member]
Sales by geographical area	6,100	5,616
Sales by significant product type	6,100	5,616
CANADA
Sales by geographical area	92,872	88,668
Sales by significant product type	92,872	88,668
KOREA, REPUBLIC OF
Sales by geographical area	49,300	32,703
Sales by significant product type	49,300	32,703
JAPAN
Sales by geographical area	8,350	13,773
Sales by significant product type	8,350	13,773
UNITED STATES
Sales by geographical area	4,571	4,081
Sales by significant product type	4,571	4,081
Other Geographic Areas [Member]
Sales by geographical area		(131)
Sales by significant product type		$ (131)