Note 4 - Balance Sheet Components - Cash and Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Cash and cash equivalents	$ 91,468	$ 143,745	$ 165,266	$ 126,870
Gross Unrealized Loss	(409)	(74)
Short-term investments	38,078	22,742
Long-term investments	1,940	16,210
Investments and Cash	131,895	182,771
Investments and Cash, Fair Value Disclosure	131,486	182,697
US Treasury Securities [Member]
Amortized Cost	20,057	25,055
Gross Unrealized Loss	(284)	(58)
Estimated Fair Value	19,773	24,997
Short-term investments	19,773	12,022
Long-term investments	0	12,975
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	12,638	7,491
Estimated Fair Value	12,581	7,491
Short-term investments	10,641	7,491
Corporate Debt Securities [Member]
Amortized Cost	7,732	6,480
Gross Unrealized Loss	(68)	(16)
Estimated Fair Value	7,664	6,464
Short-term investments	7,664	3,229
Long-term investments		3,235
Cash [Member]
Cash and Cash Equivalents, at Carrying Value	21,833	72,767
Money market funds, Fair Value	21,833	72,767
Cash and cash equivalents	21,833	72,767
Money Market Funds [Member]
Cash and Cash Equivalents, at Carrying Value	69,635	70,978
Money market funds, Fair Value	69,635	70,978
Cash and cash equivalents	$ 69,635	$ 70,978