Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Amortized Cost	$ 68,564	$ 117,944
Unrealized Gain	0	1
Unrealized Loss	(504)	(248)
Fair Value	68,060	117,697
Short-term investments	64,195	80,262
Long-term investments	3,865	37,435
Commercial Paper [Member]
Amortized Cost	12,364	50,705
Unrealized Gain	0	0
Unrealized Loss	(49)	(46)
Fair Value	12,315	50,659
Short-term investments	12,315	50,660
Long-term investments	0	0
Corporate Debt Securities [Member]
Amortized Cost	55,201	67,239
Unrealized Gain	0	1
Unrealized Loss	(447)	(202)
Fair Value	54,754	67,038
Short-term investments	50,889	29,602
Long-term investments	3,865	$ 37,435
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