Note 7 - Marketable Securities - Short-term and Long-term Held-to-Maturity Securities (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Amortized Cost	$ 93,445
Unrealized Gains	393
Unrealized Losses	(23)
Fair Value	93,815
Bank Time Deposits [Member]
Amortized Cost	5,395
Unrealized Gains	93
Unrealized Losses	0
Fair Value	5,488
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	25,003
Unrealized Gains	83
Unrealized Losses	(2)
Fair Value	25,084
Corporate Debt Securities [Member]
Amortized Cost	42,048
Unrealized Gains	211
Unrealized Losses	(11)
Fair Value	42,248
US Government Agencies Debt Securities [Member]
Amortized Cost	18,500
Unrealized Gains	6
Unrealized Losses	(10)
Fair Value	18,496
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	2,499
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 2,499

Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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