Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 15,286	$ 10,695
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	137,711	177,898
Total liabilities	6,677	22,191
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	100,685	104,743
Equity securities	16,594	24,018
Certificates of deposit and other deposits	1,163	1,164
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	16,685	45,146
Foreign exchange contracts	1,343	1,518
Metal forward and put option contracts	$ 1,241	$ 1,309
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Assets	Assets
Foreign exchange contracts	$ 5,549	$ 7,548
Metal forward and put option contracts	$ 1,128	$ 14,643
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities