Note 12 - Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

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

Description	Balance at June 30, 2018		Balance at December 31, 2017		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	239,722	$	186,107	Level 1
Available for sale securities:
Debt securities - municipal and corporate bonds		5,556		33,758	Level 2
Equity securities – mining industry		7,449		7,561	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		9,717		14,805	Level 2
Restricted cash balances:
Certificates of deposit and other deposits		1,005		1,032	Level 1
Derivative contracts:
Foreign exchange contracts		172		4,943	Level 2
Metal forward contracts		14,705		—	Level 2
Total assets	$	278,326	$	248,206
Liabilities:
Derivative contracts:
Foreign exchange contracts	$	2,330	$	—	Level 2
Metal forward contracts		—		15,531	Level 2
Total Liabilities	$	2,330	$	15,531