Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 19,051	$ 18,376
Total assets	93,170	163,918
Total liabilities	2,016	1,548
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	24,585	106,374
Equity securities	36,900	32,284
Certificates of deposit and other deposits	1,171	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	30,242	14,740
Foreign exchange contracts	98	4,657
Metal forward and put option contracts	(2,702)	40
Foreign exchange contracts	4,718	1,508
Metal forward and put option contracts	$ 174	$ 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