Note 7 - Equity Incentive Plans - Fair Value Assumptions for Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Disclosure Text Block [Abstract]
Weighted-average exercise price per share	$ 0.89	$ 17.72
Weighted-average expected term (years)	5 years 9 months 21 days	5 years
Weighted-average risk-free interest rate	2.17%	0.88%
Weighted-average expected dividend yield	$ 0	$ 0
Weighted-average volatility	73.70%	76.05%