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