Note 4 - Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Total cash equivalents	$ 33,171	$ 37,023
Restricted cash	221	557
Total assets measured at fair value	33,392	37,580
Money Market Funds [Member]
Total cash equivalents	13,461	37,023
US Treasury Securities [Member]
Total cash equivalents	19,710
Fair Value, Inputs, Level 1 [Member]
Total cash equivalents	33,171	37,023
Restricted cash	221	557
Total assets measured at fair value	33,392	37,580
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Total cash equivalents	13,461	37,023
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Total cash equivalents	19,710
Fair Value, Inputs, Level 2 [Member]
Total cash equivalents	0	0
Restricted cash	0	0
Total assets measured at fair value	0	0
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Total cash equivalents	0	$ 0
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Total cash equivalents	$ 0