Note 12 - Fair Value Measurement - Assets and Liabilities Accounted for at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Receivables from provisional concentrate sales	$ 9,031	$ 9,780
Fair Value, Measurements, Recurring [Member]
Total assets	227,979	231,608
Total liabilities	11,902	5,480
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Money market funds and other bank deposits	172,923	169,777
Equity securities – mining industry	7,098	5,002
Certificates of deposit and other bank deposits	1,076	2,200
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Debt securities - municipal and corporate bonds	32,973	29,117
Receivables from provisional concentrate sales	6,982	20,082
Foreign exchange contracts	6,533	27
Metal forward contracts	394	5,403
Foreign exchange contracts		5,288
Metal forward contracts	$ 11,902	$ 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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