Earnings Per Share (Details) (USD $)	3 Months Ended				12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Basic earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.11	$ 2.25	$ 0.79	$ (0.15)	$ 3.01	$ 3.05	$ 2.34
Income (loss) from discontinued operations (in dollars per share)					$ 0.10	$ 0.23	$ (1.66)
Earnings per share - basic (in dollars per share)	$ 0.12	$ 2.34	$ 0.80	$ (0.14)	$ 3.11	$ 3.28	$ 0.68
Diluted earnings per share:
Income from continuing operations attributable to common shareholders (in dollars per share)	$ 0.11	$ 2.24	$ 0.78	$ (0.15)	$ 2.99	$ 3.03	$ 2.34
Income (loss) from discontinued operations					$ 0.10	$ 0.24	$ (1.67)
Earnings per share - diluted (in dollars per share)	$ 0.11	$ 2.32	$ 0.79	$ (0.14)	$ 3.09	$ 3.27	$ 0.67
Dilutive stock options and performance shares					811,000	565,000	103,000
Total average common shares outstanding for the purposes of calculating diluted earnings per share					109,864,000	107,138,000	101,264,000
Options to purchase shares of common stock outstanding excluded from computation of diluted earnings per share due to its antidilutive effect						192,542	572,301