Subsequent Events - Additional Information (Detail) (USD $)	6 Months Ended		3 Months Ended				6 Months Ended	8 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Continuous Equity Program CEP II Subsequent Event	Jun. 30, 2011 Fund II Subsequent Event Home	Jun. 30, 2011 Subsequent Event	Jun. 30, 2011 Continuous Equity Program CEP II	Jun. 30, 2011 Continuous Equity Program CEP II	Jun. 30, 2011 Continuous Equity Program CEP II
Subsequent Event [Line Items]
Susequent event date					Jul. 31, 2011
Shares sold under 2009 CEP II (in shares)			256,167			553,856	1,801,766	2,234,598
Shares sold under 2009 CEP II, average sales price			$ 127.90			$ 130.56	$ 120.47	$ 118.91
Net proceeds from sales of shares sold under 2009 CEP II	$ 264,134,000	$ 306,817,000	$ 32,271,000			$ 71,225,000	$ 213,794,000	$ 261,729,000
Number of Apartment Homes acquired				94
Purchase price of Real Estate Investment acquired				$ 20,850,000