Note 4 - Balance Sheet Components - Cash and Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Cash, cash equivalents and restricted cash	$ 33,238	$ 46,013	$ 50,768	$ 143,745
Gross Unrealized Loss	(11)	(299)
Short-term investments	19,799	49,704
Investments and Cash	53,048	96,016
Investments and Cash, Fair Value Disclosure	53,037	95,717
US Treasury Securities [Member]
Amortized Cost	19,810	41,812
Gross Unrealized Loss	(11)	(270)
Estimated Fair Value	19,799	41,542
Short-term investments	19,799	41,542
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost		2,488
Estimated Fair Value		2,488
Short-term investments		2,488
Corporate Debt Securities [Member]
Amortized Cost		5,703
Gross Unrealized Loss		(29)
Estimated Fair Value		5,674
Short-term investments		5,674
Cash [Member]
Cash and Cash Equivalents, at Carrying Value	5,263	15,179
Money market funds, Fair Value	5,263	15,179
Cash, cash equivalents and restricted cash	5,263	15,179
Money Market Funds [Member]
Cash and Cash Equivalents, at Carrying Value	27,975	30,834
Money market funds, Fair Value	27,975	30,834
Cash, cash equivalents and restricted cash	$ 27,975	$ 30,834