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Fair Value (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2024
Sep. 30, 2023
Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Unrealized Gain (Loss) on Investments $ 0.4 $ (0.2) $ 0.7 $ 0.2  
Level 1 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.3   0.3   $ 0.6
Level 2 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.0   0.0   0.0
Level 3 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.0   0.0   0.0
Subsidiaries [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Unrealized Gain (Loss) on Investments 0.4 $ (0.2) 0.7 $ 0.2  
Subsidiaries [Member] | Level 1 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.3   0.3   0.6
Subsidiaries [Member] | Level 2 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.0   0.0   0.0
Subsidiaries [Member] | Level 3 [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.0   0.0   0.0
Estimate of Fair Value Measurement [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure 0.3   0.3   0.6
Estimate of Fair Value Measurement [Member] | Subsidiaries [Member] | Money Market Funds [Member]          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Investments, Fair Value Disclosure $ 0.3   $ 0.3   $ 0.6