Earnings Per Share (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.24	$ 2.23	$ 1.12	$ (0.07)	$ 0.11	$ 2.25	$ 0.79	$ (0.15)	$ 3.54	$ 3.01	$ 3.05
Income (loss) from discontinued operations (in dollars per share)									$ (0.06)	$ 0.10	$ 0.23
Earnings per share - basic (in dollars per share)	$ 0.21	$ 2.23	$ 1.12	$ (0.08)	$ 0.12	$ 2.34	$ 0.80	$ (0.14)	$ 3.48	$ 3.11	$ 3.28
Diluted earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.24	$ 2.21	$ 1.12	$ (0.07)	$ 0.11	$ 2.24	$ 0.78	$ (0.15)	$ 3.50	$ 2.99	$ 3.03
Income (loss) from discontinued operations (in dollars per share)									$ (0.05)	$ 0.10	$ 0.24
Earnings per share - diluted (in dollars per share)	$ 0.20	$ 2.21	$ 1.11	$ (0.08)	$ 0.11	$ 2.32	$ 0.79	$ (0.14)	$ 3.45	$ 3.09	$ 3.27
Dilutive stock options and performance shares									1,017,000	811,000	565,000
Total average common shares outstanding for the purposes of calculating diluted earnings per share									110,527,311	109,864,243	107,137,785
Options to purchase shares of common stock outstanding excluded from computation of diluted earnings per share due to its antidilutive effect											192,542