Net Income Per Common Share (Schedule Of Basic And Diluted Net Income Per Common Share) (Details) (USD $) In Thousands, except Per Share data, 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
Net Income Per Common Share [Abstract]
Net income	$ 41,968	$ 41,003	$ 42,541	$ 34,692	$ 33,027	$ 23,673	$ 29,759	$ 40,437	$ 160,204	$ 126,896	$ 129,263
Series A and B preferred share dividends									(20,369)	(20,233)	(20,239)
Unvested stock award participation in earnings									(579)	(594)	(554)
Numerator for basic net income per common share									139,256	106,069	108,470
Weighted average common shares outstanding									79,784	69,948	65,418
Average unvested stock awards outstanding									(468)	(396)	(373)
Denominator for basic net income per common share									79,316	69,552	65,045
Basic net income per common share									$ 1.76	$ 1.53	$ 1.67
Dividends on antidilutive convertible preferred shares									(20,071)	(19,932)	(19,932)
Unvested stock award participation in earnings									(579)	(594)	(555)
Numerator for diluted net income per common share									$ 139,554	$ 106,370	$ 108,776
Net effect of dilutive stock and option awards									71	39	100
Net effect of dilutive convertible preferred shares									309	310	304
Denominator for diluted net income per common share									79,696	69,901	65,449
Diluted net income per common share									$ 1.75	$ 1.52	$ 1.66