Note 13 - Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

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

	Balance at December 31, 2018		Balance at December 31, 2017		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	27,389	$	186,107	Level 1
Available for sale securities:
Debt securities – municipal and corporate bonds		—		33,758	Level 2
Equity securities – mining industry		6,583		7,561	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		4,184		14,805	Level 2
Derivative contracts:
Metal forward contracts		209		—	Level 2
Foreign exchange contracts		23		4,943	Level 2
Restricted cash balances:
Certificates of deposit and other bank deposits		1,025		1,032	Level 1
Total assets	$	39,413	$	248,206
Liabilities
Derivative contracts:
Metal forward contracts	$	373	$	15,531	Level 2
Foreign exchange contracts		8,595		—	Level 2
Total liabilities	$	8,968	$	15,531