Note 8 - Marketable Securities - Short-term and Long-term Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost	$ 48,397	$ 70,329
Unrealized Gains	112	1
Unrealized Losses	(22)	(242)
Fair Value	48,487	70,088
Bank Time Deposits [Member]
Amortized Cost	1,484	4,208
Unrealized Gains	22	0
Unrealized Losses	0	(25)
Fair Value	1,506	4,183
US Government Agencies Debt Securities [Member]
Amortized Cost	6,274	16,843
Unrealized Gains	1	0
Unrealized Losses	(7)	(88)
Fair Value	6,268	16,755
Corporate Debt Securities [Member]
Amortized Cost	26,944	31,769
Unrealized Gains	80	0
Unrealized Losses	(12)	(96)
Fair Value	27,012	31,673
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	10,204	17,509
Unrealized Gains	9	1
Unrealized Losses	(3)	(33)
Fair Value	10,210	$ 17,477
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	3,491
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 3,491