Note 4 - Balance Sheet Components - Cash and Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash and cash equivalents	$ 167,231	$ 126,870
Gross Unrealized Loss	(3)	0
Short-term investments	20,438	0
Long-term investments	16,282	0
Investments and Cash	203,954	126,870
Investments and Cash, Fair Value Disclosure	203,951	126,870
US Treasury Securities [Member]
Amortized Cost	23,025
Gross Unrealized Loss	(3)
Estimated Fair Value	23,022
Short-term investments	9,997
Long-term investments	13,025
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	7,192
Estimated Fair Value	7,192
Short-term investments	7,192
Corporate Debt Securities [Member]
Amortized Cost	6,506
Gross Unrealized Loss	0
Estimated Fair Value	6,506
Short-term investments	3,249
Long-term investments	3,257
Cash [Member]
Cash and Cash Equivalents, at Carrying Value	93,955	66,865
Money market funds, Fair Value	93,955	66,865
Cash and cash equivalents	93,955	66,865
Money Market Funds [Member]
Cash and Cash Equivalents, at Carrying Value	73,276	60,005
Money market funds, Fair Value	73,276	60,005
Cash and cash equivalents	$ 73,276	$ 60,005