Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 1.19	$ 1.12	$ 1.42	$ 1.06
Loss from discontinued operations (in dollars per share)				$ (0.02)
Earnings per share - basic (in dollars per share)	$ 1.19	$ 1.12	$ 1.42	$ 1.04
Diluted earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 1.18	$ 1.12	$ 1.40	$ 1.05
Loss from discontinued operations (in dollars per share)		$ (0.01)		$ (0.01)
Earnings per share - diluted (in dollars per share)	$ 1.18	$ 1.11	$ 1.40	$ 1.04
Performance shares and restricted stock units	970,000	868,000	945,000	788,000
Options to purchase shares of common stock outstanding excluded from computation of diluted earnings per share due to its antidilutive effect	0	0	0	0