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Fair Value Measurements (Fair Value Inputs, Liabilities, Quantitative Information) (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2020 | Dec. 31, 2019
Fair Value Inputs, Liabilities, Quantitative Information |  |
Long-term Debt | $ 1,033.2 | $ 1,032.3
Level 1 Inputs |  |
Fair Value Inputs, Liabilities, Quantitative Information |  |
Fair value level 1 inputs | quoted prices in active markets for identical liabilities (Level 1 inputs |
Fair Value Measured at Net Asset Value Per Share [Member] |  |
Fair Value Inputs, Liabilities, Quantitative Information |  |
Deferred Compensation Plan Assets | $ 13.1 | $ 11.8

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