Note 13 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Receivables from provisional concentrate sales	$ 7,443	$ 7,003
Fair Value, Measurements, Recurring [Member]
Certificates of deposit and other bank deposits	1,025	1,032
Total assets	39,413	248,206
Total liabilities	8,968	15,531
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Money market funds and other bank deposits	27,389	186,107
Equity securities – mining industry	6,583	7,561
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Debt securities – municipal and corporate bonds		33,758
Receivables from provisional concentrate sales	4,184	14,805
Metal forward contracts	209
Foreign exchange contracts	23	4,943
Metal forward contracts	373	15,531
Foreign exchange contracts	$ 8,595

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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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Amount due from parties in nontrade transactions, classified as other.

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