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Marketable Securities - Schedule of Available-For-Sale Securities (Details) - USD ($)
Sep. 30, 2023
Dec. 31, 2022
Available-for-sale securities:    
Amortized Cost $ 14,858,000 $ 22,992,000
Gross Unrealized Gain 1,000 2,000
Gross Unrealized (Losses) (385,000) (715,000)
Estimated Fair Value 14,474,000 22,279,000
Held-to-maturity securities:    
Amortized Cost   0
Tax-exempt municipal securities    
Available-for-sale securities:    
Amortized Cost 11,654,000 15,852,000
Gross Unrealized Gain 1,000 2,000
Gross Unrealized (Losses) (263,000) (507,000)
Estimated Fair Value 11,392,000 15,347,000
Corporate debt securities    
Available-for-sale securities:    
Amortized Cost 3,204,000 7,140,000
Gross Unrealized Gain 0 0
Gross Unrealized (Losses) (122,000) (208,000)
Estimated Fair Value 3,082,000 $ 6,932,000
Term deposits    
Held-to-maturity securities:    
Amortized Cost 16,400,000  
Gross Unrealized Gain 0  
Gross Unrealized (Losses) 0  
Estimated Fair Value $ 16,400,000