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Stock-Based Compensation Plans (Details 4) - Performance awards - $ / shares
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 Arrangement By Share Based Payment Award Maximum Measurement Period 3 years    
Performance awards      
Outstanding at the beginning of the period (in shares) 267,129 251,770 251,163
Granted (in shares) 80,512 100,965 81,708
Increase (decrease) in awards based on performance (in shares) (16,760) 5,990 49,323
Converted to restricted stock (in shares) (73,072) (88,477) (128,482)
Forfeited (in shares) (4,377) (3,119) (1,942)
Outstanding at the ending of the period (in shares) 253,432 267,129 251,770
Weighted average grant date fair value per award      
Outstanding at the beginning of the period (in dollars per share) $ 157.21 $ 155.25 $ 136.74
Granted (in dollars per share) 200.75 155.31 176.59
Change in awards based on performance (in dollars per share) 142.03 148.79 119.26
Converted to restricted stock (in dollars per share) 142.03 148.79 118.75
Forfeited (in dollars per share) 166.44 160.33 159.39
Outstanding at the ending of the period (in dollars per share) $ 176.27 $ 157.21 $ 155.25
Grants in period based on shareholder metrics (in shares) 47,502 62,043 49,374
Grants in period based on financial metrics (in shares) 33,010 38,922 32,334