Commitments to Acquire/Dispose of Real Estate (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Commitments to Acquire Real Estate
Properties Acquired-Total	5
Rental Units Acquired - Total	851
Purchase Price - Total	$ 252,125
Commitments to Dispose of Real Estate
Rental Units Disposed-Total	1,961
Properties Disposed - Total	6
Sales Price-Total	173,900
Rental Properties [Member]
Commitments to Acquire Real Estate
Properties Acquired-Total	5
Rental Units Acquired - Total	851
Purchase Price - Total	223,025
Commitments to Dispose of Real Estate
Rental Units Disposed-Total	1,961
Properties Disposed - Total	6
Sales Price-Total	173,900
Land Parcels (three) [Member]
Commitments to Acquire Real Estate
Properties Acquired-Total	0
Rental Units Acquired - Total	0
Purchase Price - Total	$ 29,100