Note 12 - Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Balance at December 31, 2014		Balance at December 31, 2013		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	209,665	$	212,175	Level 1
Available for sale securities:
Equity securities – mining industry		4,920		7,019	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		17,696		17,672	Level 2
Derivative contracts:
Base metal forward contracts		11,347		4,461	Level 2
Restricted cash balances:
Certificates of deposit and other bank deposits		883		5,217	Level 1
Total assets	$	244,511	$	246,544