Note 12 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Receivables from provisional concentrate sales	$ 22,234	$ 9,967
Fair Value, Measurements, Recurring [Member]
Total assets	238,423	231,608
Total liabilities	5,109	5,480
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Money market funds and other bank deposits	176,786	169,777
Equity securities – mining industry	5,104	5,002
Certificates of deposit and other bank deposits	2,200	2,200
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Debt securities – municipal and corporate bonds	36,505	29,117
Receivables from provisional concentrate sales	17,210	20,082
Metal forward contracts	254	5,403
Foreign exchange contracts	364	27
Metal forward contracts	2,386	192
Foreign exchange contracts	$ 2,723	$ 5,288

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 debt securities categorized neither as held-to-maturity nor trading.

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