Share-Based Compensation and Benefit Plans (Employee Share Purchase Plan Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation [Abstract]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	15,330	18,986	20,797
Weighted Average Fair Value Of Shares Purchased Under Employee Share Purchase Plan	$ 90.93	$ 89.89	$ 82.33
Employee Stock Ownership Plan (ESOP), Compensation Expense	$ 0.2	$ 0.3	$ 0.4