Note 6 - Fair Value Measurements - Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Corporate and municipal debt securities	$ 5,054	$ 4,973
Total assets	22,846
Corporate Debt Securities [Member]
Corporate and municipal debt securities	5,054
Money Market Funds [Member]
Money market accounts	17,792
Fair Value, Inputs, Level 1 [Member]
Total assets	22,846
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Corporate and municipal debt securities	5,054
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Money market accounts	$ 17,792