Note 6 - Business Segments and Sales of Products (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) oz T	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) oz T	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Number of Reportable Segments			5
Derivative, Loss on Derivative	$ 5,000		$ 3,300	$ 1,200
Derivative, Gain on Derivative		$ 1,300
Accounts Receivable, after Allowance for Credit Loss, Current, Total	26,003		26,003		$ 11,952
Accounts Receivable, Allowance for Credit Loss, Ending Balance	$ 0		$ 0		$ 0
Silver Contracts [Member]
Metals Contained in Concentrates (Ounce) | oz	2,600,000		2,600,000
Gold 1 [Member]
Metals Contained in Concentrates (Ounce) | oz	7,969		7,969
Zinc [Member]
Metals Contained in Concentrates (Ounce) | T	9,983		9,983
Lead [Member]
Metals Contained in Concentrates (Ounce) | T	7,405		7,405