Note 4 - Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Total cash equivalents	$ 24,102
Restricted cash	221
Total assets measured at fair value	24,323
Money Market Funds [Member]
Total cash equivalents	12,651
US Treasury Securities [Member]
Total cash equivalents	11,451
Fair Value, Inputs, Level 1 [Member]
Total cash equivalents	12,651	$ 37,023
Restricted cash	221	557
Total assets measured at fair value	12,872	37,580
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Total cash equivalents	12,651	$ 37,023
Fair Value, Inputs, Level 2 [Member]
Total cash equivalents	11,451
Total assets measured at fair value	11,451
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Total cash equivalents	$ 11,451