Note 3 - Cash, Cash Equivalents, and Marketable Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
US Treasury Securities [Member]
Amortized cost	$ 12,192	$ 19,883
Gross unrealized gains	0	1
Gross unrealized losses	(1)	0
Fair value	12,191	19,884
Money Market Funds [Member]
Amortized cost	5,660	5,113
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	5,660	5,113
Cash Equivalents [Member]
Amortized cost	17,852	24,996
Gross unrealized gains	0	1
Gross unrealized losses	(1)	0
Fair value	17,851	24,997
Cash [Member]
Amortized cost	3,881	3,824
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	3,881	3,824
Cash and Cash Equivalents [Member]
Amortized cost	21,733	28,820
Gross unrealized gains	0	1
Gross unrealized losses	(1)	0
Fair value	21,732	28,821
Us Treasury Securities with Maturity Greater than 90 Days but Less than 1 Year [Member]
Amortized cost	6,179	6,179
Gross unrealized gains	0	0
Gross unrealized losses	(1)	0
Fair value	6,178	6,179
Marketable Securities [Member]
Amortized cost	6,179	6,179
Gross unrealized gains	0	0
Gross unrealized losses	(1)	0
Fair value	$ 6,178	$ 6,179