Real Estate Real Estate Acquisitions (Details) (USD $)	6 Months Ended
	Jun. 30, 2012
Acquired Properties	5
Units - acquired	1,356
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 693,709,000
Consolidated Rental Properties [Member]
Acquired Properties	5
Units - acquired	1,356
Business Acquisition, Cost of Acquired Entity, Purchase Price	669,969,000
Land Parcel [Member]
Acquired Properties	0
Land parcels acquired	2
Units - acquired	0
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 23,740,000