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Stock-Based Compensation (Compensation Expense) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Stock-based compensation $ 31.1 $ 25.5 $ 20.6
Tax benefit related to stock-based compensation expense 2.5 3.0 7.8
Unrecognized compensation cost related to non-vested stock-based compensation arrangements $ 20.1    
Unrecognized compensation cost expected to be recognized over weighted average period (in years) 1 year 8 months 26 days    
Tax benefits related to stock options exercised and vesting of restricted stock and RSUs $ 3.3 3.4 6.2
Restricted Stock Units (RSUs) [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Stock-based compensation 29.4 21.7 14.2
Unrecognized compensation cost related to non-vested stock-based compensation arrangements 19.9    
Stock Options [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Stock-based compensation 0.9 1.6 3.1
Unrecognized compensation cost related to non-vested stock-based compensation arrangements 0.1    
Restricted Stock [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Stock-based compensation 0.8 $ 2.2 $ 3.3
Unrecognized compensation cost related to non-vested stock-based compensation arrangements $ 0.1