Quarterly report pursuant to Section 13 or 15(d)

Note 4 - Marketable Securities - Fair Value of Marketable Securities (Details)

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Note 4 - Marketable Securities - Fair Value of Marketable Securities (Details) - Fair Value, Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2022
Dec. 31, 2021
Total marketable securities $ 38,015 $ 40,405
Fair Value, Inputs, Level 1 [Member]    
Total marketable securities 0 0
Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 38,015 40,405
Fair Value, Inputs, Level 3 [Member]    
Total marketable securities 0 0
US Government Agencies Debt Securities [Member]    
Total marketable securities 28,041 29,421
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Total marketable securities 0 0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 28,041 29,421
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Total marketable securities 0 0
Commercial Paper and Corporate Bonds [Member]    
Total marketable securities 9,974 10,984
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 1 [Member]    
Total marketable securities 0 0
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 9,974 10,984
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 3 [Member]    
Total marketable securities $ 0 $ 0