Note 4 - Fair Value Measurements - Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Marketable Securities	$ 151,663
Fair Value	151,663
Corporate Debt Securities [Member]
Marketable Securities	87,760
Fair Value	87,760
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	37,682
Fair Value	37,682
Certificates of Deposit [Member]
Marketable Securities	19,667
Fair Value	19,667
Asset-Backed Securities [Member]
Marketable Securities	6,554
Fair Value	6,554
Fair Value, Recurring [Member]
Total assets	161,101	$ 130,005
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Marketable Securities	87,760
Fair Value	87,760
Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Marketable Securities	9,438	130,005
Fair Value	9,438	130,005
Fair Value, Recurring [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	37,682
Fair Value	37,682
Fair Value, Recurring [Member] | Certificates of Deposit [Member]
Marketable Securities	19,667
Fair Value	19,667
Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Marketable Securities	6,554
Fair Value	6,554
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total assets	47,120	130,005
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Marketable Securities	0
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities	9,438	130,005
Fair Value	9,438	130,005
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	37,682
Fair Value	37,682
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Marketable Securities	0
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-Backed Securities [Member]
Marketable Securities	0
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total assets	113,981	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Marketable Securities	87,760
Fair Value	87,760
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities	0	0
Fair Value	0	0
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	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Marketable Securities	19,667
Fair Value	19,667
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-Backed Securities [Member]
Marketable Securities	6,554
Fair Value	6,554
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
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Marketable Securities	0	0
Fair Value	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
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Marketable Securities	0
Fair Value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-Backed Securities [Member]
Marketable Securities	0
Fair Value	$ 0