Real Estate Real Estate Acquisitions (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Land parcels acquired		6	7
Properties acquired	1	9	21	1
Units - acquired		1,896	6,198
Business Acquisition, Cost of Acquired Entity, Purchase Price		$ 1,047,545,000	$ 1,597,111,000
Company's Portion [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price			102,500,000
Land purchase price			76,100,000
Consolidated Rental Properties [Member]
Properties acquired		9	21
Units - acquired		1,896	6,198
Business Acquisition, Cost of Acquired Entity, Purchase Price		906,305,000	1,383,048,000
Land Parcel [Member]
Units - acquired		0	0
Business Acquisition, Cost of Acquired Entity, Purchase Price		141,240,000	202,313,000
Unaffiliated Parties [Member]
Properties acquired			0
Units - acquired			0
Business Acquisition, Cost of Acquired Entity, Purchase Price			11,750,000
Joint Venture Partner [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price			75,700,000
Land purchase price			$ 57,900,000