Note 8 - Equity Incentive Plans - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Share-based compensation expense	$ 252	$ 103	$ 946	$ 1,208
Research and Development Expense [Member]
Share-based compensation expense	63	26	174	349
General and Administrative Expense [Member]
Share-based compensation expense	$ 189	$ 77	$ 772	$ 859