Investments in Real Estate Entities - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended					9 Months Ended	1 Months Ended									1 Months Ended					1 Months Ended			9 Months Ended	3 Months Ended
	Apr. 30, 2011	Sep. 30, 2011 Property Community Home Location Investment	Sep. 30, 2011 Community Home Location Investment	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Minimum	Sep. 30, 2011 Maximum	Sep. 30, 2011 Maximum Fund I and Fund II	Apr. 30, 2011 5.24 % Fixed Rate Mortgage Loan Due in June 2013	Apr. 30, 2011 5.86% Fixed Rate Mortgage Due in May 2019	Apr. 30, 2011 Real Estate Community	Apr. 30, 2011 Real Estate Boston Property	Apr. 30, 2011 Real Estate San Francisco County, California Property	Apr. 30, 2011 Real Estate California UDR, Inc Property	Apr. 30, 2011 Land Boston Community	Sep. 30, 2011 Unconsolidated Real Estate Investments Home	Sep. 30, 2011 Unconsolidated Real Estate Investments Fund II Home	Jul. 31, 2011 Unconsolidated Real Estate Investments Fund II Captain Parker Arms - Lexington, MA Home	Sep. 30, 2011 Unconsolidated Real Estate Investments Fund II Captain Parker Arms - Lexington, MA Home	Sep. 30, 2011 Unconsolidated Real Estate Investments Fund I Home	Sep. 30, 2011 Fund II	Sep. 30, 2011 Fund I	Apr. 30, 2011 UDR, Inc	Apr. 30, 2011 4.75% Fixed Rate Mortgage Loan Due in August 2015 Fairfax Towers	Apr. 30, 2011 Fairfax Towers Home	Sep. 30, 2011 Fairfax Towers	Sep. 30, 2011 AvalonBay Value Added Fund II, LP Fund II Home	Sep. 30, 2011 AvalonBay Value Added Fund II, LP Fund II Parent Company
Investment Holdings [Line Items]
Non-monetary exchange transaction, description	In April 2011, the Company completed an exchange of assets with UDR, Inc. (“UDR”). The transaction included exchanging a portfolio of three communities and a parcel of land owned by the Company for a portfolio of six UDR communities and $26,000,000 in cash. The Company’s portfolio consisted of two properties and a small land parcel located in metropolitan Boston and one property located in San Francisco. The UDR portfolio is located in Southern California (Los Angeles, Orange County and San Diego). The Company accounted for the exchange as a non-monetary transaction based on the carrying value of the assets relinquished by the Company.
Partial gain in non-monetary exchange transaction	$ 7,675,000
Assets disposed of in non-cash asset exchange											3	2	1		1
Communities acquired in non-cash asset exchange														6
Boot received from exchange of real estate																							26,000,000
Mortgage note assumed									55,400,000															44,044,000
Mortgage note relinquished in non-monetary exchange transaction										55,800,000
Number of Apartment Homes acquired																9,013	4,242	94	94	3,724
Number of Apartment Homes acquired																									415
Purchase price of real estate investment acquired																		20,850,000							89,200,000
Transaction costs for asset exchange and acquisition			1,010,000																							1,010,000
Number of investments in unconsolidated real estate entities		6	6
Costs in excess of equity in underlying net assets of the respective investments		9,427,000	9,427,000		9,566,000
ownership interest percentage in unconsolidated real estate entities						15.20%	50.00%
Number of apartment homes sold																											105
Proceeds from exchange/sale of real estate, net of selling costs		34,475,000	55,479,000	186,058,000																							33,100,000
Gain on sale of real estate assets			21,391,000	72,220,000																							12,445,000	1,743,000
Percentage of total capital contributions made by partner equal to shortfall payment								10.00%
Maximum amount of total capital contributions made by partner equal to shortfall payment																					$ 7,095,000	$ 7,500,000