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Note 7 - Investments (Tables)
9 Months Ended
Sep. 30, 2022
Notes Tables  
Marketable Securities [Table Text Block]
   

Amortized

   

Unrealized

   

Unrealized

         
   

Cost Basis

   

Gains

   

Losses

   

Fair Value

 

Marketable securities:

                               

US government

  $ 46,554     $     $ (102 )   $ 46,452  

Corporate bonds

    4,416             (10 )     4,406  

Commercial paper

    12,336             (24 )     12,312  

Certificates of deposit

    4,074             (19 )     4,055  

Total marketable securities

  $ 67,380     $     $ (155 )   $ 67,225  
Investments Classified by Contractual Maturity Date [Table Text Block]
   

September 30,

   

December 31,

 
   

2022

   

2021

 

Maturities within one year

  $ 67,225     $ 44,779  

Maturities after one year through three years

          675  

Total investments

  $ 67,225     $ 45,454