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
Sep. 30, 2020
Dec. 31, 2019
Total marketable securities $ 20,826 $ 3,995
Fair Value, Inputs, Level 1 [Member]    
Total marketable securities
Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 20,826 3,995
Fair Value, Inputs, Level 3 [Member]    
Total marketable securities
US Government Agencies Debt Securities [Member]    
Total marketable securities 12,827 1,998
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Total marketable securities
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 12,827 1,998
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Total marketable securities
Bank Certificates of Deposit [Member]    
Total marketable securities 1,748
Bank Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]    
Total marketable securities
Bank Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 1,748
Bank Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]    
Total marketable securities
Commercial Paper and Corporate Bonds [Member]    
Total marketable securities 6,251 1,997
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 1 [Member]    
Total marketable securities
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]    
Total marketable securities 6,251 1,997
Commercial Paper and Corporate Bonds [Member] | Fair Value, Inputs, Level 3 [Member]    
Total marketable securities