Note 5 - Investments, Available-for-sale - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost	$ 38,853	$ 68,564
Unrealized Gain	2	0
Unrealized Loss	(200)	(504)
Fair Value	38,655	68,060
Short-term investments	37,697	64,195
Long-term investments	958	3,865
Commercial Paper [Member]
Amortized Cost	5,442	12,364
Unrealized Gain	0	0
Unrealized Loss	(16)	(49)
Fair Value	5,426	12,315
Short-term investments	5,426	12,315
Long-term investments	0	0
Corporate Debt Securities [Member]
Amortized Cost	29,459	55,201
Unrealized Gain	2	0
Unrealized Loss	(178)	(447)
Fair Value	29,283	54,754
Short-term investments	28,325	50,889
Long-term investments	958	3,865
US Treasury Securities [Member]
Amortized Cost	2,953
Unrealized Gain	0
Unrealized Loss	(1)
Fair Value	2,952
Short-term investments	2,952
Long-term investments	0
US Government Agencies Debt Securities [Member]
Amortized Cost	999	999
Unrealized Gain	0	0
Unrealized Loss	(5)	(8)
Fair Value	994	991
Short-term investments	994	991
Long-term investments	$ 0	$ 0