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Share-Based Compensation and Benefit Plans (Employee Share Purchase Plan Activity) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Payment Arrangement, Noncash Expense [Abstract]      
Stock Issued During Period, Shares, Employee Stock Purchase Plans 22,496 22,032 15,330
Weighted Average Fair Value Of Shares Purchased Under Employee Share Purchase Plan $ 95.97 $ 105.93 $ 90.93
Employee Stock Ownership Plan (ESOP), Compensation Expense $ 0.3 $ 0.4 $ 0.2