Share-Based Compensation and Benefit Plans (Employee Stock Purchase Plan Activity) (Details) (Employee Stock Purchase Plan [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Stock Purchase Plan [Member]
Compensation expense for benefit plans	$ 1.8	$ 1.7	$ 1.5
Income tax benefit from compensation expense for benefit plans	$ 0.7	$ 0.6	$ 0.6
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	77,000	100,600	114,600
Average grant-date fair value of shares issued during the period in compensation and benefit plans other than stock options	$ 130.12	$ 95.51	$ 75.42