Note 10 - Equity Incentive Plans - Total Stock-based Compensation Recognized for Options (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Stock-based compensation	$ 3,421	$ 2,604	$ 6,551	$ 3,855
Research and Development Expense [Member]
Stock-based compensation	2,383	644	4,410	1,223
General and Administrative Expense [Member]
Stock-based compensation	$ 1,038	$ 1,960	$ 2,141	$ 2,632