Note 12 - Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

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

Description	Balance at September 30, 2020		Balance at December 31, 2019		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	98,669	$	62,452	Level 1
Available for sale securities:
Equity securities – mining industry		17,362		6,207	Level 1
Trade accounts receivable:
Receivables from concentrate and carbon sales		28,464		11,952	Level 2
Restricted cash balances:
Certificates of deposit and other deposits		1,053		1,025	Level 1
Derivative contracts:
Foreign exchange contracts		1,009		1,184	Level 2
Metal forward and put option contracts		—		—	Level 2
Total assets	$	146,557	$	82,820
Liabilities:
Derivative contracts:
Foreign exchange contracts	$	4,130	$	1,437	Level 2
Metal forward and put option contracts		10,261		5,777	Level 2
Total liabilities	$	14,391	$	7,214