Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2011 Property Community Home Location Investment		Sep. 30, 2010	Sep. 30, 2011 Community Home Location Investment		Sep. 30, 2010	Dec. 31, 2008
Significant Accounting Policies [Line Items]
Number of operating apartment communities owned	184			184
Number of apartment homes included in operating apartment communities owned	53,826			53,826
Number of states where operating apartment communities owned are located	10			10
Number of communities with apartments under reconstruction	8			8
Number of apartment homes under reconstruction	2,377			2,377
Number of owned communities under construction	15			15
Expected number of apartment homes under construction	3,600			3,600
Communities under development rights	29			29
Expected number of apartment homes in communities to be developed	8,679			8,679
Shares excluded from computation of earnings per share amount				320,698		1,039,724
Forfeiture rate based on the average forfeiture activity over the estimated life of stock options				0.90%
Impairment loss - land holdings	$ 14,052			$ 14,052			$ 9,952
Expensed costs related to abandoned pursuits, including abandonment of Development Rights, and costs incurred in pursuing the disposition of assets for which the disposition did not occur	581		737	1,627		1,685
Proceed from environmental contamination matters						3,300
Recoveries as a reduction in the legal and professional fees						1,200
Unconsolidated Real Estate Investments
Significant Accounting Policies [Line Items]
Debt Amount	1,058,887	[1]		1,058,887	[1]
Unconsolidated Real Estate Investments | Other Development Joint Ventures | Aria at Hathorne - Danvers, MA
Significant Accounting Policies [Line Items]
Debt Amount	$ 1,860	[1],[2]		$ 1,860	[1],[2]

[1] The Company has not guaranteed the debt of its unconsolidated investees and bears no responsibility for the repayment, other than the construction and completion and related financing guarantee for Avalon Chrystie Place I associated with the construction completion and occupancy certificate.

[2] As of September 30, 2011, the amounts under this borrowing have not been repaid and the lender has declared an event of default with respect to the note and required the venture to pay a default rate of interest, which is not material to the Company. Although the Company has not guaranteed the debt of Aria at Hathorne nor does it have any obligation to fund the debt should the venture be unable to do so, the Company has the right to cure any event of default by the venture. The Company determined that the value of its investment was impaired and this impairment was other than temporary, recognizing a charge in the third quarter of 2011.