Note 4 - Fair Value Measurements - Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Marketable Securities	$ 105,780
Corporate Debt Securities [Member]
Marketable Securities	72,768
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	22,661
Certificates of Deposit [Member]
Marketable Securities	5,654
Asset-Backed Securities [Member]
Marketable Securities	4,697
Fair Value, Recurring [Member]
Total assets	117,081	$ 130,005
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Marketable Securities	72,768
Fair Value, Recurring [Member] \| Cash and Cash Equivalents [Member]
Marketable Securities	11,301	130,005
Fair Value, Recurring [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	22,661
Fair Value, Recurring [Member] \| Certificates of Deposit [Member]
Marketable Securities	5,654
Fair Value, Recurring [Member] \| Asset-Backed Securities [Member]
Marketable Securities	4,697
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Total assets	33,962	130,005
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Marketable Securities	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash and Cash Equivalents [Member]
Marketable Securities	11,301	130,005
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable Securities	22,661
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Certificates of Deposit [Member]
Marketable Securities	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Asset-Backed Securities [Member]
Marketable Securities	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Total assets	83,119	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Marketable Securities	72,768
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash and Cash Equivalents [Member]
Marketable Securities	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, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Certificates of Deposit [Member]
Marketable Securities	5,654
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Asset-Backed Securities [Member]
Marketable Securities	4,697
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, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash and Cash Equivalents [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
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Certificates of Deposit [Member]
Marketable Securities	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Asset-Backed Securities [Member]
Marketable Securities	$ 0