Net Income Per Common Share (Components Of Computation Of Basic And Diluted Net Income Per Common Share) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income	$ 40,037	$ 41,003	$ 128,542	$ 118,236
Series A and B preferred share dividends	(5,270)	(5,105)	(15,751)	(15,223)
Unvested stock award participation in earnings	(91)	(148)	(296)	(434)
Numerator for basic net income per common share	34,676	35,750	112,495	102,579
Weighted average common shares outstanding	98,581	84,147	94,324	77,852
Average unvested stock awards outstanding	(510)	(465)	(516)	(461)
Denominator for basic net income per common share	98,071	83,682	93,808	77,391
Basic net income per common share	$ 0.35	$ 0.43	$ 1.20	$ 1.33
Net income	40,037	41,003	128,542	118,236
Dividends on antidilutive convertible preferred shares	(5,195)	(5,031)	(15,528)	(14,999)
Unvested stock award participation in earnings	(91)	(148)	(296)	(434)
Numerator for diluted net income per common share	$ 34,751	$ 35,824	$ 112,718	$ 102,803
Weighted average common shares outstanding	98,581	84,147	94,324	77,852
Average unvested stock awards outstanding	(510)	(465)	(516)	(461)
Net effect of dilutive stock and option awards	132	77	119	74
Net effect of dilutive convertible preferred shares	309	309	309	309
Denominator for diluted net income per common share	98,512	84,068	94,236	77,774
Diluted net income per common share	$ 0.35	$ 0.43	$ 1.20	$ 1.32