Note 6 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Fair value	$ 67,225
Corporate Debt Securities [Member]
Fair value	4,406
US Treasury and Government [Member]
Fair value	46,452
Certificates of Deposit [Member]
Fair value	4,055
Fair Value, Recurring [Member]
Fair value		$ 67,225	$ 45,454
Total assets at fair value			66,856
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Fair value		4,406	8,652
Fair Value, Recurring [Member] \| US Treasury and Government [Member]
Fair value			19,307
Fair Value, Recurring [Member] \| Certificates of Deposit [Member]
Fair value	4,055		3,003
Fair Value, Recurring [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Fair value			14,492
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value		46,452	19,307
Total assets at fair value			40,709
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Fair value		0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury and Government [Member]
Fair value			19,307
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Certificates of Deposit [Member]
Fair value	0		0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Fair value			0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value		20,773	26,147
Total assets at fair value			26,147
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Fair value		4,406	8,652
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury and Government [Member]
Fair value			0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Certificates of Deposit [Member]
Fair value	$ 4,055		3,003
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Fair value			14,492
US Government Corporations and Agencies Securities [Member] \| Fair Value, Recurring [Member]
Cash equivalents, fair value		46,452
US Government Corporations and Agencies Securities [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash equivalents, fair value		46,452
US Government Corporations and Agencies Securities [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash equivalents, fair value		0
Money Market Funds [Member] \| Fair Value, Recurring [Member]
Cash equivalents, fair value			21,402
Money Market Funds [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash equivalents, fair value			21,402
Money Market Funds [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash equivalents, fair value			$ 0
Commercial Paper [Member] \| Fair Value, Recurring [Member]
Cash equivalents, fair value		12,312
Commercial Paper [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash equivalents, fair value		0
Commercial Paper [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash equivalents, fair value		$ 12,312