Note 12 - Fair Value Measurement (Details) - Assets and Liabilities Accounted for at Fair Value - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 16,401	$ 6,792
Derivative contracts:
Base metal forward contracts	283
Restricted cash balances:
Total assets	171,213	244,511
Derivative contracts:
Base metal forward contracts	283
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	155,209	209,665
Non-current investments:
Equity securities – mining industry	1,515	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	$ 13,490	17,696
Derivative contracts:
Base metal forward contracts		11,347
Derivative contracts:
Base metal forward contracts		$ 11,347