Note 5 - Marketable Securities - Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost	$ 128,196	$ 151,965
Unrealized gains	147	64
Unrealized Losses	(110)	(366)
Fair Value	128,233	151,663
Marketable Securities	128,233	151,663
Corporate Debt Securities [Member]
Amortized Cost	54,256	87,998
Unrealized gains	74	12
Unrealized Losses	(49)	(250)
Fair Value	54,281	87,760
Marketable Securities	54,281	87,760
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	28,507	37,680
Unrealized gains	30	33
Unrealized Losses	(3)	(31)
Fair Value	28,534	37,682
Marketable Securities	28,534	37,682
Certificates of Deposit [Member]
Amortized Cost	18,850	19,689
Unrealized gains	17	16
Unrealized Losses	(1)	(38)
Fair Value	18,866	19,667
Marketable Securities	18,866	19,667
Asset-Backed Securities [Member]
Amortized Cost	10,456	6,598
Unrealized gains	23	3
Unrealized Losses	(7)	(47)
Fair Value	10,472	6,554
Marketable Securities	10,472	$ 6,554
US Treasury Securities [Member]
Amortized Cost	16,127
Unrealized gains	3
Unrealized Losses	(50)
Fair Value	16,080
Marketable Securities	$ 16,080