Note 4 - Marketable Securities - Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized Cost	$ 132,670	$ 128,196
Unrealized gains	72	147
Unrealized Losses	(161)	(110)
Fair Value	132,581	128,233
Marketable Securities	132,581	128,233
Corporate Debt Securities [Member]
Amortized Cost	61,948	54,256
Unrealized gains	33	74
Unrealized Losses	(67)	(49)
Fair Value	61,914	54,281
Marketable Securities	61,914	54,281
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	30,130	28,507
Unrealized gains	6	30
Unrealized Losses	(12)	(3)
Fair Value	30,124	28,534
Marketable Securities	30,124	28,534
Certificates of Deposit [Member]
Amortized Cost	17,931	18,850
Unrealized gains	13	17
Unrealized Losses	(1)	(1)
Fair Value	17,943	18,866
Marketable Securities	17,943	18,866
US Treasury Securities [Member]
Amortized Cost	12,733	16,127
Unrealized gains	0	3
Unrealized Losses	(75)	(50)
Fair Value	12,658	16,080
Marketable Securities	12,658	16,080
Asset-Backed Securities [Member]
Amortized Cost	9,928	10,456
Unrealized gains	20	23
Unrealized Losses	(6)	(7)
Fair Value	9,942	10,472
Marketable Securities	$ 9,942	$ 10,472