Note 5 - Cash, Cash Equivalents and Investments - Cash Equivalents and Investments Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair value	$ 21,400
Total	46,583	$ 56,885
Fair Value, Inputs, Level 1 [Member]
Total	28,751	56,885
Fair Value, Inputs, Level 2 [Member]
Total	17,832	0
Fair Value, Inputs, Level 3 [Member]
Total	0	0
Money Market Funds [Member]
Money market funds, included in cash equivalents	25,183	56,885
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Money market funds, included in cash equivalents	25,183	56,885
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Money market funds, included in cash equivalents	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Money market funds, included in cash equivalents	0	$ 0
US Treasury Securities [Member]
Fair value	2,674
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value	2,674
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value	0
US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value	0
Debt Security, Government, Non-US [Member]
Fair value	894
Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value	894
Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value	0
Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value	0
Asset-Backed Securities [Member]
Fair value	497
Asset-Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value	0
Asset-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value	497
Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value	0
Corporate Bond Securities [Member]
Fair value	17,335
Corporate Bond Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value	0
Corporate Bond Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value	17,335
Corporate Bond Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value	$ 0