Note 2 - Business Segments and Sales of Products (Details Textual) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) Segment	Jun. 30, 2023 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Derivative, Gain (Loss) on Derivative, Net, Total	$ 12.5	$ 8.2	$ 9.4	$ 9.1
Number of Reportable Segments | Segment			4
Zinc [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1.4		$ 1.4
Lucky Friday [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Business interruption insurance proceeds received	17.8		35.2
Keno Hill [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 1.1		$ 1.1