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Stock-Based Compensation (Summary Of Nonvested Shares) (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Performance Share Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fully Vested Undistributed Retirement-eligible units (in shares) 503,283 619,783  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Share Units, Nonvested at beginning of year (in shares) 682,811    
Share Units, Granted (in shares) 304,384    
Share Units, Unearned or forfeited (in shares) (35,120)    
Undistributed Vested Units (in shares) (235,275)    
Share Units, Vested and distributed (in shares) (176,923)    
Share Units, Nonvested at end of year (in shares) 539,877 682,811  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Weighted-average Fair Value per Unit, Nonvested at beginning of year (in dollars per share) $ 56.58    
Weighted-average Fair Value per Unit, Granted (in dollars per share) 67.42 $ 62.88 $ 59.16
Weighted-average Fair Value per Unit, Unearned or forfeited (in dollars per share) 64.40    
Weighted-average Fair Value per Unit, Vested and undistributed (in dollars per share) 62.28    
Weighted-average Fair Value per Unit, Vested and distributed (in dollars per share0 44.13    
Weighted-average Fair Value per Unit, Nonvested at end of year (in dollars per share) $ 63.79 $ 56.58  
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fully Vested Undistributed Retirement-eligible units (in shares) 79,854 26,557  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Share Units, Nonvested at beginning of year (in shares) 155,253    
Share Units, Granted (in shares) 132,526    
Share Units, Unearned or forfeited (in shares) (11,802)    
Undistributed Vested Units (in shares) (53,297)    
Share Units, Vested and distributed (in shares) (2,403)    
Share Units, Nonvested at end of year (in shares) 220,277 155,253  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Weighted-average Fair Value per Unit, Nonvested at beginning of year (in dollars per share) $ 57.38    
Weighted-average Fair Value per Unit, Granted (in dollars per share) 65.89    
Weighted-average Fair Value per Unit, Unearned or forfeited (in dollars per share) 62.75    
Weighted-average Fair Value per Unit, Vested and undistributed (in dollars per share) 61.99    
Weighted-average Fair Value per Unit, Vested and distributed (in dollars per share0 54.30    
Weighted-average Fair Value per Unit, Nonvested at end of year (in dollars per share) $ 61.13 $ 57.38