Note 9 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Receivables from provisional concentrate sales	$ 7,696	$ 8,149
Fair Value, Recurring [Member]
Total assets	263,813	267,177
Total liabilities	4,750	37,881
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Recurring [Member]
Money market funds and other bank deposits	198,193	210,010
Equity securities	23,931	14,470
Certificates of deposit and other deposits	1,041	1,053
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member]
Receivables from provisional concentrate sales	17,828	36,437
Foreign exchange contracts	2,414	5,207
Metal forward and put option contracts	20,406	0
Foreign exchange contracts	529	8
Metal forward and put option contracts	$ 4,221	$ 37,873

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

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Fair value of financial and nonfinancial obligations.

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