Note 12 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Receivables from provisional concentrate sales	$ 9,780	$ 16,401
Fair Value, Measurements, Recurring [Member]
Total assets	231,608	171,213
Total liabilities	5,480
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Money market funds and other bank deposits	169,777	155,209
Equity securities – mining industry	5,002	1,515
Certificates of deposit and other bank deposits	2,200	999
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Debt securities – municipal and corporate bonds	29,117
Receivables from provisional concentrate sales	20,082	13,490
Metal forward contracts	5,403
Foreign exchange contracts	27
Metal forward contracts	192
Foreign exchange contracts	$ 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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