Note 12 - Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

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

	Balance at December 31, 2017		Balance at December 31, 2016		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	186,107	$	169,777	Level 1
Available for sale securities:
Debt securities – municipal and corporate bonds		33,758		29,117	Level 2
Equity securities – mining industry		7,561		5,002	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		14,805		20,082	Level 2
Derivative contracts:
Metal forward contracts		—		5,403	Level 2
Foreign exchange contracts		4,943		27	Level 2
Restricted cash balances:
Certificates of deposit and other bank deposits		1,032		2,200	Level 1
Total assets	$	248,206	$	231,608
Liabilities
Derivative contracts:
Metal forward contracts	$	15,531	$	192	Level 2
Foreign exchange contracts		—		5,288	Level 2
Total liabilities	$	15,531	$	5,480