Note 7 - Fair Value Measurements - Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Corporate, municipal debt and treasury securities	$ 5,147	$ 4,973
Total assets	31,094
Corporate Debt Securities [Member]
Corporate, municipal debt and treasury securities	5,147
Money Market Funds [Member]
Money market accounts	25,947
Fair Value, Inputs, Level 1 [Member]
Total assets	31,094
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Corporate, municipal debt and treasury securities	5,147
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Money market accounts	$ 25,947