Note 4 - Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Total cash equivalents	$ 12,101	$ 33,171
Restricted cash	221	221
Total assets measured at fair value	12,322	33,392
Money Market Funds [Member]
Total cash equivalents	12,101	13,461
US Treasury Securities [Member]
Total cash equivalents	0	19,710
Fair Value, Inputs, Level 1 [Member]
Total cash equivalents	12,101	33,171
Restricted cash	221	221
Total assets measured at fair value	12,322	33,392
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Total cash equivalents	12,101	13,461
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Total cash equivalents	$ 0	$ 19,710