Earnings Per Share (Schedule Of Net Income Attributable To Common Stockholders) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share [Abstract]
Net income	$ 26,443	$ 67,930	$ 81,049	$ 83,544	$ 84,073	[1]	$ 62,731	[1]	$ 56,942	[1]	$ 17,647	[1]	$ 258,966	$ 221,393	$ 52,995
Less: Net income attributable to participating securities													(2,310)	(2,230)	(475)
Net income attributable to common shareholders													$ 256,656	$ 219,163	$ 52,520

[1] Basic and diluted earnings per common share ("EPS") for each quarter is computed using the weighted average shares outstanding during that quarter, while EPS for the year is computed using the weighted average shares outstanding for the year. As a result, the sum of the EPS for each of the four quarters may not equal the EPS for the year.