Note 5 - Equity - Stock based Compensation (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 expense	$ 514	$ 433	$ 1,041	$ 838
General and Administrative Expense [Member]
Stock-based compensation expense	350	332	711	641
Research and Development Expense [Member]
Stock-based compensation expense	$ 164	$ 101	$ 330	$ 197