Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from provisional concentrate sales	$ 15,121	$ 10,695
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	158,404	177,898
Total liabilities	2,198	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	106,786	104,743
Equity securities	20,778	24,018
Certificates of deposit and other deposits	1,166	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	15,595	45,146
Foreign exchange contracts	5,404	1,518
Metal forward and put option contracts	$ 8,675	$ 1,309
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Assets	Assets
Foreign exchange contracts	$ 2,198	$ 7,548
Metal forward and put option contracts	$ 0	$ 14,643
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities