Note 3 - Marketable Securities - Fair Value and Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair value	$ 43,343	$ 0
Gross unrealized losses	(40)
Maturity, Less Than 12 Months [Member]
Fair value	47,029
Gross unrealized losses	(40)
Maturity, Greater Than 12 Months [Member]
Fair value	0
Gross unrealized losses	0
Corporate Debt Securities [Member]
Gross unrealized losses	(36)
Corporate Debt Securities [Member] | Maturity, Less Than 12 Months [Member]
Fair value	32,529
Gross unrealized losses	(36)
Corporate Debt Securities [Member] | Maturity, Greater Than 12 Months [Member]
Fair value	0
Gross unrealized losses	0
Commercial Paper [Member]
Gross unrealized losses	0
Commercial Paper [Member] | Maturity, Less Than 12 Months [Member]
Fair value	8,891
Gross unrealized losses	0
Commercial Paper [Member] | Maturity, Greater Than 12 Months [Member]
Fair value	0
Gross unrealized losses	0
Money Market Funds [Member]
Gross unrealized losses	0
Money Market Funds [Member] | Maturity, Less Than 12 Months [Member]
Fair value	3,686
Gross unrealized losses	0
Money Market Funds [Member] | Maturity, Greater Than 12 Months [Member]
Fair value	0
Gross unrealized losses	0
Debt Security, Corporate, Non-US [Member]
Gross unrealized losses	(4)
Debt Security, Corporate, Non-US [Member] | Maturity, Less Than 12 Months [Member]
Fair value	1,923
Gross unrealized losses	(4)
Debt Security, Corporate, Non-US [Member] | Maturity, Greater Than 12 Months [Member]
Fair value	0
Gross unrealized losses	$ 0