Earnings per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted average common shares—basic	131,664,296	133,299,458	132,301,814	133,199,304
Plus incremental shares from: Assumed exercise of options	456,939	546,601	484,720	543,841
Weighted average common shares-diluted	132,121,235	133,846,059	132,786,534	133,743,145
Earnings per share: Basic (usd per share)	$ 1.39	$ 1.26	$ 4.04	$ 3.71
Earnings per share: Diluted (usd per share)	$ 1.39	$ 1.25	$ 4.02	$ 3.69