Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Type (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total stock-based compensation expense	$ 5,191	$ 14,601	$ 10,075
Time-based Options [Member]
Total stock-based compensation expense	4,467	9,235	8,739
Performance Options [Member]
Total stock-based compensation expense	233	4,840	133
Restricted Stock Units (RSUs) [Member]
Total stock-based compensation expense	0	0	86
Employee Stock Purchase Plan Award [Member]
Total stock-based compensation expense	$ 491	$ 526	$ 1,117