Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 19,767	$ 18,376
Total assets	148,644	163,918
Total liabilities	4,267	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	80,169	106,374
Equity securities	32,873	32,284
Certificates of deposit and other deposits	1,163	1,165
Credit agreement carrying and fair value	140,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	30,508	14,740
Foreign exchange contracts	685	4,657
Metal forward and put option contracts	3,246	4,698
Foreign exchange contracts	4,267	1,508
Metal forward and put option contracts	$ 0	$ 40
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