Note 6 - Business Segments and Sales of Products (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) oz T	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) oz T	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Number of Reportable Segments			5
Derivative, Loss on Derivative	$ 9,600		$ 12,900	$ 100
Derivative, Gain on Derivative		$ 1,100
Accounts Receivable, after Allowance for Credit Loss, Current, Total	$ 28,464		$ 28,464		$ 11,952
Accounts Receivable, Allowance for Credit Loss, Ending Balance					$ 0
Silver Contracts [Member]
Metals Contained in Concentrates (Ounce) | oz	1,200,000		1,200,000
Gold [Member]
Metals Contained in Concentrates (Ounce) | oz	3,436		3,436
Zinc [Member]
Metals Contained in Concentrates (Ounce) | T	17,097		17,097
Lead [Member]
Metals Contained in Concentrates (Ounce) | T	3,207		3,207