Subsequent Events (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			4 Months Ended				3 Months Ended
	Mar. 31, 2012	Apr. 03, 2012	Mar. 31, 2011	Apr. 30, 2012	May 01, 2012 properties	Apr. 26, 2012	Apr. 25, 2012	Apr. 02, 2012 Series D Preferred Stock [Member]	Apr. 02, 2012 Series F Preferred Stock [Member]
Subsequent Events [Line Items]
Preferred stock redeemed, shares								4,000	7,000
Preferred stock redeemed, amount	$ 0		$ 0					$ 100,000	$ 175,000
Preferred stock redeemed, rate								7.875%	7.625%
Senior unsecured notes issued amount		600,000
Senior unsecured notes issued rate		0.04125
Senior unsecured notes net proceeds	0	594,000	1,381,086
Conversion notices received, amount				125,563		162	125,000
Conversion notices received, rate			4.75%
Secured debt extinguished, amount				185,000
Secured debt extinguished, rate				4.25%
Number of properties entered into joint venture agreement					39
Number of buildings acquired					3
Number of properties in portfolio					42
Percentage of partnership owned					50.00%
Percentage of interest owned by minority	5.00%				50.00%
Company investment in transaction					$ 509,500