Consolidated Statements of Stockholders' Equity and Comprehensive Income/(Loss) (Unaudited) (USD $) In Thousands, except Share data	Total	Preferred Stock	Common Stock	Paid - in Capital	Distributions in Excess of Net Income	Accumulated Other Comprehensive Income/(Loss)	Non-controlling interest
Beginning Balance at Dec. 31, 2010	$ 1,610,030	$ 131,710	$ 1,825	$ 2,450,141	$ (973,864)	$ (3,469)	$ 3,687
Beginning Balance, Shares at Dec. 31, 2010		6,209,374	182,496,330
Comprehensive income/(loss)
Net loss	(13,224)				(13,224)
Net income attributable to non-controlling interest	88						88
Other comprehensive income
Unrealized gain on sale of marketable securities reclassified into earnings	(3,492)					(3,492)
Unrealized gain on derivative financial instruments	(3,553)					(3,553)
Allocation to redeemable non-controlling interests	229					229
Comprehensive income /(loss)	(19,952)				(13,224)	(6,816)	88
Issuance of common and restricted shares	7,250		6	7,244
Issuance of common and restricted shares, Shares			687,339
Issuance of common shares through public offering	325,105		134	324,971
Issuance of common shares through public offering, Shares			13,474,955
Redemption of 141,200 shares of 6.75% Series G Redeemable, Shares		(141,200)
Redemption of 141,200 shares of 6.75% Series G Redeemable shares, Value	(3,597)	(3,530)		108	(175)
Adjustment for conversion of non-controlling interests of unitholders in operating partnerships, Shares	1,894		1,894
Adjustment for conversion of non-controlling interests of unitholders in operating partnerships	48		2	46
Common stock distributions declared ($0.385 per share)	(74,329)				(74,329)
Preferred stock distributions declared-Series E ($0.6644 per share)	(1,862)				(1,862)
Preferred stock distributions declared-Series G ($0.843715 per share)	(2,833)				(2,833)
Adjustment to reflect redemption value of redeemable non-controlling interests	(9,212)				(9,212)
Ending Balance at Jun. 30, 2011	$ 1,830,648	$ 128,180	$ 1,967	$ 2,782,510	$ (1,075,499)	$ (10,285)	$ 3,775
Ending Balance, Shares at Jun. 30, 2011		6,068,174	196,660,518