Note 3 - Fair Value Measurements - Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Marketable Securities	$ 133,277	$ 151,663
Corporate Debt Securities [Member]
Marketable Securities	41,633	87,760
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	48,889	37,682
Certificates of Deposit [Member]
Marketable Securities	19,547	19,667
Asset-Backed Securities [Member]
Marketable Securities	8,426	6,554
US Treasury Securities [Member]
Marketable Securities	14,782
Fair Value, Recurring [Member]
Total assets	133,277	161,101
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Marketable Securities	41,633	87,760
Fair Value, Recurring [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	48,889	37,682
Fair Value, Recurring [Member] | Certificates of Deposit [Member]
Marketable Securities	19,547	19,667
Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Marketable Securities	8,426	6,554
Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Marketable Securities		9,438
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Marketable Securities	14,782
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total assets	63,671	47,120
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	48,889	37,682
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-Backed Securities [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities		9,438
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Marketable Securities	14,782
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total assets	69,606	113,981
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Marketable Securities	41,633	87,760
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Marketable Securities	19,547	19,667
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-Backed Securities [Member]
Marketable Securities	8,426	6,554
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities		0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Marketable Securities	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] | Corporate Debt Securities [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-Backed Securities [Member]
Marketable Securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities		$ 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member]
Marketable Securities	$ 0