Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Total stock-based compensation expense	$ 896	$ 2,007
Time-based Options [Member]
Total stock-based compensation expense	678	1,807
Performance Options [Member]
Total stock-based compensation expense	117	84
Employee Stock Purchase Plan Award [Member]
Total stock-based compensation expense	$ 101	$ 116