Note 2 - Fair Value of Financial Instruments - Summary of Fair Value Hierarchy for Financial Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Assets, fair value	$ 41,121
Fair Value, Recurring [Member]
Assets, fair value	41,121	$ 50,396
Fair Value, Recurring [Member] | Money Market Securities [Member]
Assets, fair value	4,698	2,073
Fair Value, Recurring [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets, fair value	19,437	35,468
Fair Value, Recurring [Member] | Federal Agency Notes [Member]
Assets, fair value	15,000	4,423
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Assets, fair value	1,986	8,432
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets, fair value	4,698	2,073
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Securities [Member]
Assets, fair value	4,698	2,073
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Federal Agency Notes [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value	36,423	48,323
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Securities [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets, fair value	19,437	35,468
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Federal Agency Notes [Member]
Assets, fair value	15,000	4,423
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Assets, fair value	1,986	8,432
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Securities [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Federal Agency Notes [Member]
Assets, fair value	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Assets, fair value	$ 0	$ 0