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Retirement and Share-based Compensation Plans (Schedule of Stock Options Outstanding, By Exercise Price Range) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Options outstanding and vested, aggregate intrinsic value $ 8.3    
Proceeds from stock options exercised 4.4 $ 10.0 $ 14.0
Stock Option Plans For Officers, Directors And Employees      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Options exercised in period, total intrinsic value $ 3.4 $ 3.0 $ 1.5
Exercise Price Range I      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Exercise price range, lower range limit $ 9.27    
Exercise price range, upper range limit $ 11.35    
Stock options outstanding and vested, number of awards 147,500    
Stock options outstanding and vested, remaining life (yrs) 1 year 2 months 8 days    
Stock options outstanding and vested, weighted-average exercise price per share $ 9.74    
Exercise Price Range II      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Exercise price range, lower range limit 12.04    
Exercise price range, upper range limit $ 24.79    
Stock options outstanding and vested, number of awards 681,413    
Stock options outstanding and vested, remaining life (yrs) 11 months 8 days    
Stock options outstanding and vested, weighted-average exercise price per share $ 22.12    
Exercise Price Range, All Options      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Exercise price range, lower range limit 9.27    
Exercise price range, upper range limit $ 24.79    
Stock options outstanding and vested, number of awards 828,913    
Stock options outstanding and vested, remaining life (yrs) 11 months 23 days    
Stock options outstanding and vested, weighted-average exercise price per share $ 19.91