Earnings Per Share (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.22	$ 2.06	$ 1.19	$ 0.22	$ 0.24	$ 2.23	$ 1.12	$ (0.07)	$ 3.69	$ 3.54	$ 3.01
Income (loss) from discontinued operations (in dollars per share)										$ (0.06)	$ 0.10
Earnings per share - basic (in dollars per share)	$ 0.22	$ 2.06	$ 1.19	$ 0.22	$ 0.21	$ 2.23	$ 1.12	$ (0.08)	$ 3.69	$ 3.48	$ 3.11
Diluted earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.22	$ 2.04	$ 1.18	$ 0.22	$ 0.24	$ 2.21	$ 1.12	$ (0.07)	$ 3.66	$ 3.50	$ 2.99
Income (loss) from discontinued operations (in dollars per share)										$ (0.05)	$ 0.10
Earnings per share - diluted (in dollars per share)	$ 0.22	$ 2.04	$ 1.18	$ 0.22	$ 0.20	$ 2.21	$ 1.11	$ (0.08)	$ 3.66	$ 3.45	$ 3.09
Dilutive stock options and performance shares									822,000	1,017,000	811,000
Total average common shares outstanding for the purposes of calculating diluted earnings per share									110,806,000	110,527,000	109,864,000
Options to purchase shares of common stock outstanding excluded from computation of diluted earnings per share due to its antidilutive effect									0	0	0