Note 7 - Fair Value Measurements - Fair Value of Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Marketable securities	$ 49,987	$ 25,920
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	38,862	65,637
Marketable securities	9,881	7,602
Total	66,439	73,531
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash and cash equivalents	17,696	292
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Marketable securities	40,106	18,318
Total	40,106	18,318
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Cash and cash equivalents	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Marketable securities	0	0
Total	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Cash and cash equivalents	$ 0	$ 0