Note 5 - Fair Value Measurements - Fair Value of Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Marketable securities	$ 42,675	$ 49,987
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Marketable securities	11,344	9,881
Total	73,395	66,439
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash [Member]
Cash	50,165	38,862
Cash and cash equivalents	50,165	38,862
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Cash	11,886	17,696
Cash and cash equivalents	11,886	17,696
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Marketable securities	31,331	40,106
Total	31,331	40,106
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash [Member]
Cash	0	0
Cash and cash equivalents	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Cash	0	0
Cash and cash equivalents	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Marketable securities	0	0
Total	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash [Member]
Cash	0	0
Cash and cash equivalents	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Cash	0	0
Cash and cash equivalents	$ 0	$ 0