Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost	$ 93,885	$ 117,944
Unrealized Gain	0	1
Unrealized Loss	(944)	(248)
Fair Value	92,941	117,697
Short-term investments	83,360	80,262
Long-term investments	9,581	37,435
Commercial Paper [Member]
Amortized Cost	35,643	50,705
Unrealized Gain	0	0
Unrealized Loss	(191)	(46)
Fair Value	35,452	50,659
Short-term investments	35,452	50,660
Long-term investments	0	0
Corporate Debt Securities [Member]
Amortized Cost	58,242	67,239
Unrealized Gain	0	1
Unrealized Loss	(753)	(202)
Fair Value	57,489	67,038
Short-term investments	47,908	29,602
Long-term investments	$ 9,581	$ 37,435