Note 3 - Investments and Fair Value of Financial Instruments - Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Total assets measured at fair value	$ 50,700	$ 57,973
Total assets measured at fair value	(50,700)	(57,973)
Fair Value, Inputs, Level 1 [Member]
Total assets measured at fair value	50,700	57,973
Total assets measured at fair value	(50,700)	(57,973)
Fair Value, Inputs, Level 2 [Member]
Cash and Cash equivalents		0
Total assets measured at fair value	(0)
Total assets measured at fair value	0
Fair Value, Inputs, Level 3 [Member]
Total assets measured at fair value	0	0
Total assets measured at fair value	0	0
Money Market Funds [Member]
Cash and Cash equivalents	50,700	57,973
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and Cash equivalents	50,700	57,973
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and Cash equivalents	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and Cash equivalents	$ 0	$ 0