Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Amortized Cost	$ 75,275	$ 117,944
Unrealized Gain	0	1
Unrealized Loss	(857)	(248)
Fair Value	74,418	117,697
Short-term investments	72,481	80,262
Long-term investments	1,937	37,435
Commercial Paper [Member]
Amortized Cost	18,869	50,705
Unrealized Gain	0	0
Unrealized Loss	(85)	(46)
Fair Value	18,784	50,659
Short-term investments	18,784	50,660
Long-term investments	0
Corporate Debt Securities [Member]
Amortized Cost	55,407	67,239
Unrealized Gain	0	1
Unrealized Loss	(768)	(202)
Fair Value	54,639	67,038
Short-term investments	53,697	29,602
Long-term investments	942	$ 37,435
US Government Agencies Debt Securities [Member]
Amortized Cost	999
Unrealized Gain	0
Unrealized Loss	(4)
Fair Value	995
Short-term investments	0
Long-term investments	$ 995