Note 12 - Fair Value Measurement (Details) - Assets and Liabilities Accounted for at Fair Value - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 14,220	$ 6,792
Derivative contracts:
Total assets	206,519	244,511
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	191,574	209,665
Available for sale securities:
Equity securities – mining industry	2,672	4,920
Restricted cash balances:
Certificates of deposit and other bank deposits	957	883
Fair Value, Inputs, Level 2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	7,781	17,696
Derivative contracts:
Metal forward contracts	$ 3,535	$ 11,347