Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost	$ 11,451	$ 68,564
Unrealized Gain	0	0
Unrealized Loss	(31)	(504)
Fair Value	11,420	68,060
Short-term investments	11,420	64,195
Long-term investments	0	3,865
Commercial Paper [Member]
Amortized Cost	0	12,364
Unrealized Gain	0	0
Unrealized Loss	0	(49)
Fair Value	0	12,315
Short-term investments	0	12,315
Long-term investments	0	0
Corporate Debt Securities [Member]
Amortized Cost	4,960	55,201
Unrealized Gain	0	0
Unrealized Loss	(28)	(447)
Fair Value	4,932	54,754
Short-term investments	4,932	50,889
Long-term investments	0	3,865
US Treasury Securities [Member]
Amortized Cost	5,491
Unrealized Gain	0
Unrealized Loss	0
Fair Value	5,491
Short-term investments	5,491
Long-term investments	0
US Government Agencies Debt Securities [Member]
Amortized Cost	1,000	999
Unrealized Gain	0	0
Unrealized Loss	(3)	(8)
Fair Value	997	991
Short-term investments	997	991
Long-term investments	$ 0	$ 0