Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 20,568	$ 17,538
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds and other bank deposits	133,910	26,868
Equity securities	68,305	33,158
Certificates of deposit and other deposits	1,172	1,177
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	102,702	31,515
Foreign exchange contracts	684	0
Metal forward contracts	3,068	18,039
Foreign exchange contracts	2,120	10,176
Metal forward contracts	$ 6,502	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities