Note 8 - Share-based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-based compensation expense	$ 304	$ 384	$ 623	$ 800
Research and Development Expense [Member]
Share-based compensation expense	130	211	257	417
Selling, General and Administrative Expenses [Member]
Share-based compensation expense	$ 174	$ 173	$ 366	$ 383