Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost	$ 3,981	$ 68,564
Unrealized Gain	0	0
Unrealized Loss	(10)	(504)
Fair Value	3,971	68,060
Short-term investments	3,971	64,195
Long-term investments	0	3,865
Corporate Debt Securities [Member]
Amortized Cost	3,981	55,201
Unrealized Gain	0	0
Unrealized Loss	(10)	(447)
Fair Value	3,971	54,754
Short-term investments	$ 3,971	50,889
Long-term investments		3,865
Commercial Paper [Member]
Amortized Cost		12,364
Unrealized Gain		0
Unrealized Loss		(49)
Fair Value		12,315
Short-term investments		12,315
Long-term investments		0
US Government Agencies Debt Securities [Member]
Amortized Cost		999
Unrealized Gain		0
Unrealized Loss		(8)
Fair Value		991
Short-term investments		991
Long-term investments		$ 0