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Fair Value Measurements (Financial Instruments Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Recurring [Member]
$ in Millions
Mar. 31, 2023
USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities $ 105.0
Total Assets at Fair Value 105.0
Corporate Debt Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 11.5
Mutual Funds [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Trading Securities at Fair Value 93.4
Equity Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.1
Fair Value, Inputs, Level 1 [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 105.0
Total Assets at Fair Value 105.0
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 11.5
Fair Value, Inputs, Level 1 [Member] | Mutual Funds [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Trading Securities at Fair Value 93.4
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.1
Fair Value, Inputs, Level 2 [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.0
Total Assets at Fair Value 0.0
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.0
Fair Value, Inputs, Level 2 [Member] | Mutual Funds [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Trading Securities at Fair Value 0.0
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.0
Fair Value, Inputs, Level 3 [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.0
Total Assets at Fair Value 0.0
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities 0.0
Fair Value, Inputs, Level 3 [Member] | Mutual Funds [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Trading Securities at Fair Value 0.0
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Marketable Securities $ 0.0