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Stock-Based Compensation (Share-based Compensation Expense) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 10.1 $ 8.8 $ 17.0
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 2.7 2.0 2.4
RSU compensation expense      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 5.1 4.7 4.3
PSU compensation expense      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 2.3 $ 2.1 $ 10.3