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Note 11 - Fair Value Measurements (Tables)
3 Months Ended
Mar. 31, 2024
Notes Tables  
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
  

March 31, 2024

 
  

Total

  

Level 1

  

Level 2

  

Level 3

 

Money market funds

 $125,235  $125,235  $-  $- 

Certificates of deposit

  166,157   -   166,157   - 

Corporate debt securities

  60,380   -   60,380   - 

U.S. treasuries and government agency bonds

  571,579   -   571,579   - 

Auction-rate securities backed by student-loan notes

  518   -   -   518 

Mutual funds and money market funds under deferred compensation plan

  57,373   57,373   -   - 

Total

 $981,242  $182,608  $798,116  $518 
  

December 31, 2023

 
  

Total

  

Level 1

  

Level 2

  

Level 3

 

Money market funds

 $135,514  $135,514  $-  $- 

Certificates of deposit

  127,123   -   127,123   - 

Corporate debt securities

  95,101   -   95,101   - 

U.S. treasuries and government agency bonds

  358,409   -   358,409   - 

Auction-rate securities backed by student-loan notes

  567   -   -   567 

Mutual funds and money market funds under deferred compensation plan

  54,836   54,836   -   - 

Total

 $771,550  $190,350  $580,633  $567