Note 12 - Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2018

Notes Tables

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

Description	Balance at March 31, 2018		Balance at December 31, 2017		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	212,569	$	186,107	Level 1
Available for sale securities:
Debt securities – municipal and corporate bonds		34,358		33,758	Level 2
Equity securities – mining industry		7,652		7,561	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		19,713		14,805	Level 2
Restricted cash balances:
Certificates of deposit and other bank deposits		1,005		1,032	Level 1
Derivative contracts:
Metal forward contracts		630		—	Level 2
Foreign exchange contracts		3,122		4,943	Level 2
Total assets	$	279,049	$	248,206
Liabilities:
Derivative contracts:
Metal forward contracts	$	7,066	$	15,531	Level 2
Foreign exchange contracts		248		—	Level 2
Total Liabilities	$	7,314	$	15,531