Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost	$ 32,396	$ 68,564
Unrealized Gain	0	0
Unrealized Loss	(99)	(504)
Fair Value	32,297	68,060
Short-term investments	32,297	64,195
Long-term investments	0	3,865
Commercial Paper [Member]
Amortized Cost	2,986	12,364
Unrealized Gain	0	0
Unrealized Loss	(5)	(49)
Fair Value	2,981	12,315
Short-term investments	2,981	12,315
Long-term investments	0	0
Corporate Debt Securities [Member]
Amortized Cost	16,025	55,201
Unrealized Gain	0	0
Unrealized Loss	(83)	(447)
Fair Value	15,942	54,754
Short-term investments	15,942	50,889
Long-term investments	0	3,865
US Treasury Securities [Member]
Amortized Cost	12,386
Unrealized Gain	0
Unrealized Loss	(5)
Fair Value	12,381
Short-term investments	12,381
Long-term investments	0
US Government Agencies Debt Securities [Member]
Amortized Cost	999	999
Unrealized Gain	0	0
Unrealized Loss	(6)	(8)
Fair Value	993	991
Short-term investments	993	991
Long-term investments	$ 0	$ 0