Note 12 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Receivables from provisional concentrate sales	$ 12,307	$ 9,780
Fair Value, Measurements, Recurring [Member]
Total assets	220,433	231,608
Total liabilities	1,968	5,480
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Money market funds and other bank deposits	164,113	169,777
Equity securities – mining industry	4,729	5,002
Certificates of deposit and other deposits	1,098	2,200
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Debt securities - municipal and corporate bonds	37,816	29,117
Receivables from provisional concentrate sales	9,183	20,082
Foreign exchange contracts	2,286	27
Metal forward contracts	1,208	5,403
Foreign exchange contracts	585	5,288
Metal forward contracts	$ 1,383	$ 192

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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