Note 3 - Fair Value of Financial Instruments - Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Money Market Funds [Member]
Money market funds, Fair Value	$ 17,710	$ 31,403
Fair Value, Recurring [Member]
Total assets	32,586	36,361
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Investments, Fair Value Disclosure	14,876	4,958
Fair Value, Recurring [Member] | Money Market Funds [Member]
Money market funds, Fair Value	17,710	31,403
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total assets	17,710	31,403
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Investments, Fair Value Disclosure	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Money market funds, Fair Value	17,710	31,403
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total assets	14,876	4,958
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Investments, Fair Value Disclosure	14,876	4,958
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Money market funds, Fair Value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total assets	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member]
Investments, Fair Value Disclosure	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Money market funds, Fair Value	$ 0	$ 0