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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 18.3 $ 15.3 $ 13.7
Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock granted 0.4 0.6 0.3
Grant date fair value $ 30.44 $ 23.85 $ 30.43
Restricted Stock Units [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards vesting period 1 year    
Restricted Stock Units [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards vesting period 3 years    
Performance Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted 0.3 0.3 0.3
Grant date fair value $ 26.38 $ 22.01 $ 28.10
Awards vesting period 3 years    
Performance Share Units [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance target range 0.00%    
Performance Share Units [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance target range 250.00%