Real Estate Activity Schedule of Business Acquisitions (Details) (Multifamily, USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 apartmentunits
Colonial Grand at Brier Falls (Raleigh, NC)
Total units	350
Effective acquisition date	January 10, 2012
Purchase price	$ 45.0
Colonial Grand at Fairview (Dallas, TX)
Total units	256
Effective acquisition date	May 30, 2012
Purchase price	$ 29.8