Summary Of Major Accounting Policies - Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Basic earnings per share:
Net income per consolidated statements of income	$ 235,658	$ 200,531	$ 188,353
Income allocable to paticipating securities	0	(709)	(1,324)
Net Income (Loss) Available to Common Stockholders, Basic	235,658	199,822	187,029
Basic shares outstanding	108,308	109,119	109,532
Basic earnings per share	$ 2.18	$ 1.83	$ 1.71
Diluted earnings per share:
Income allocable to participating securities	0	(706)	(1,318)
Earnings allocable to diluted common shareholders	$ 235,658	$ 199,825	$ 187,035
Diluted shares outstanding	109,001	109,535	110,053
Diluted earnings per share	$ 2.16	$ 1.82	$ 1.70