Note 12 - Fair Value Measurement (Details) - Assets and Liabilities Accounted for at Fair Value - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 12,970	$ 6,792
Derivative contracts:
Total assets	189,627	244,511
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	174,454	209,665
Available for sale securities:
Equity securities – mining industry	2,003	4,920
Restricted cash balances:
Certificates of deposit and other bank deposits	999	883
Fair Value, Inputs, Level 2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	10,384	17,696
Derivative contracts:
Metal forward contracts	$ 1,787	$ 11,347