Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 16,218	$ 13,691
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds and other bank deposits	22,273	106,374
Equity securities	40,915	32,284
Certificates of deposit and other deposits	1,184	1,165
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	40,124	17,940
Foreign exchange contracts	805	4,657
Metal forward contracts	2,625	40
Foreign exchange contracts	2,010	1,508
Metal forward contracts	$ 886	$ 4,698
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Metal forward contracts	Assets	Assets
Metal forward contracts	Liabilities	Liabilities