Stockholders Equity (Narrative) (Detail) (USD $)	1 Months Ended	2 Months Ended	12 Months Ended			6 Months Ended	12 Months Ended				1 Months Ended	12 Months Ended
	Oct. 30, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Preferred Stock [Member]	Dec. 31, 2012 Preferred Stock [Member]	Dec. 31, 2012 Continuous Offering Program [Member]	Dec. 31, 2011 Continuous Offering Program [Member]	Dec. 31, 2010 Continuous Offering Program [Member]	Jan. 31, 2013 Subsequent Event [Member]	Dec. 31, 2012 Directors And Employees [Member]	Dec. 31, 2011 Directors And Employees [Member]	Dec. 31, 2010 Directors And Employees [Member]
Stockholders' Equity [Line Items]
Proceeds from issuance of common stock								$ 142,000,000	$ 231,700,000	$ 10,400,000
Additional shares issued								10,500,000	17,800,000	811,000
Preferred equity shares capital			150,950,000	240,049,000	11,743,000	674,000	9,700,000
Common stock repurchase program	100,000,000
Shares repurchased		3,000,000									638,000
Average cost per share			$ 11.80								$ 11.43
Value of stock repurchased			35,100,000								7,300,000
Related compensation costs												$ 4,400,000	$ 3,200,000	$ 1,300,000