Note 11 - Benefit Plans - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Total stock-based compensation expense	$ 1,951	$ 2,451	$ 3,964	$ 4,674
Share-Based Payment Arrangement, Option [Member]
Total stock-based compensation expense	1,951	2,438	3,953	4,660
Restricted Stock Awards [Member]
Total stock-based compensation expense	0	13	11	14
General and Administrative Expense [Member]
Total stock-based compensation expense	1,048	1,327	2,184	2,577
Research and Development Expense [Member]
Total stock-based compensation expense	$ 903	$ 1,124	$ 1,780	$ 2,097