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Fair Value Measurements (Fair Value Inputs, Liabilities, Quantitative Information) (Details) - USD ($)
$ in Millions
Mar. 31, 2020
Dec. 31, 2019
Fair Value Inputs, Liabilities, Quantitative Information    
Long-term Debt, Gross $ 1,073.8 $ 1,040.8
Unamortized Debt Issuance Expense 8.3 8.5
Level 1 Inputs    
Fair Value Inputs, Liabilities, Quantitative Information    
Long-term debt, fair value 1,000.0  
Fair Value Measured at Net Asset Value Per Share [Member]    
Fair Value Inputs, Liabilities, Quantitative Information    
Deferred Compensation Plan Assets $ 10.6 $ 11.8