Condensed Consolidated Statements of Equity (Unaudited) (USD $)	Total	Stockholders' Equity Common Stock Number of Shares	Stockholders' Equity Additional Paid-In Capital	Stockholders' Equity Accumulated Deficit
Beginning balance at Dec. 31, 2009	$ 1,071,317,000	$ 1,405,000	$ 1,251,996,000	$ (182,084,000)
Beginning balance, shares at Dec. 31, 2009		140,590,686
Issuance of common stock, shares		21,404,471
Issuance of common stock	206,829,000	212,000	206,617,000
Offering costs	(23,784,000)		(23,784,000)
Issuance of restricted common stock, shares		150,000
Issuance of restricted common stock	1,500,000	2,000	1,498,000
Amortization of nonvested share based compensation	365,000		365,000
Issuance of common stock under the DRIP, shares		2,743,824
Issuance of common stock under the DRIP	26,066,000	27,000	26,039,000
Repurchase of common stock, shares		(2,019,832)
Repurchase of common stock	(19,158,000)	(20,000)	(19,138,000)
Distributions	(54,300,000)			(54,300,000)
Adjustment to redeemable noncontrolling interests	275,000		(26,000)	301,000
Net income loss attributable to controlling interest	(302,000)			(302,000)
Ending balance at Jun. 30, 2010	1,208,808,000	1,626,000	1,443,567,000	(236,385,000)
Ending balance, shares at Jun. 30, 2010		162,869,149
Beginning balance at Dec. 31, 2010	1,487,246,000	2,026,000	1,795,413,000	(310,193,000)
Beginning balance, shares at Dec. 31, 2010		202,643,705
Issuance of common stock, shares		21,767,175
Issuance of common stock	211,630,000	220,000	211,410,000
Offering costs	(15,355,000)		(15,355,000)
Issuance of restricted common stock, shares		25,000
Amortization of nonvested share based compensation	1,542,000		1,542,000
Issuance of common stock under the DRIP, shares		3,909,772
Issuance of common stock under the DRIP	37,143,000	39,000	37,104,000
Repurchase of common stock, shares		(1,834,141)
Repurchase of common stock	(17,684,000)	(18,000)	(17,666,000)
Distributions	(79,450,000)			(79,450,000)
Net income loss attributable to controlling interest	3,321,000			3,321,000
Ending balance at Jun. 30, 2011	$ 1,628,393,000	$ 2,267,000	$ 2,012,448,000	$ (386,322,000)
Ending balance, shares at Jun. 30, 2011		226,511,511