Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost	$ 117,944
Unrealized Gain	1
Unrealized Loss	(248)
Fair Value	117,697	$ 0
Short-term investments	80,262	0
Long-term investments	37,435	0
Mature in less than one year, amortized cost	80,336
Mature in less than one year, fair value	80,262
Mature in one to two years, amortized cost	37,608
Mature in one to two years, fair value	37,435
Total, amortized cost	117,944
Total, fair value	117,697	$ 0
Corporate Debt Securities [Member]
Amortized Cost	67,239
Unrealized Gain	1
Unrealized Loss	(202)
Fair Value	67,038
Short-term investments	29,602
Long-term investments	37,435
Total, amortized cost	67,239
Total, fair value	67,038
Commercial Paper [Member]
Amortized Cost	50,705
Unrealized Gain	0
Unrealized Loss	(46)
Fair Value	50,659
Short-term investments	50,660
Long-term investments	0
Total, amortized cost	50,705
Total, fair value	$ 50,659