Notes Payable, Unsecured Notes and Credit Facility - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended					1 Months Ended									3 Months Ended
	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Minimum	Dec. 31, 2011 Maximum	Mar. 31, 2011 Variable Rate Secured Mortgage Note	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 4.75% Fixed Rate Mortgage Loan Due in August 2015 Fairfax Towers	Apr. 30, 2011 Variable Rate Tax-Exempt, Secured Mortgage Note	Aug. 31, 2011 Fixed Rate Mortgage 7.25% Due October 2011	Sep. 30, 2011 Unsecured Senior Notes	Oct. 31, 2011 5.88% fixed rate secured mortgage note maturing January 2019	Nov. 30, 2011 Fixed Rate Mortgage 4.95% Due April 2013	Sep. 30, 2011 Variable Rate Unsecured Credit Facility	Dec. 31, 2011 Variable Rate Unsecured Credit Facility	Dec. 31, 2010 Variable Rate Unsecured Credit Facility	Sep. 30, 2011 Variable Rate Unsecured Credit Facility Minimum	Sep. 30, 2011 Variable Rate Unsecured Credit Facility Maximum	Dec. 31, 2011 Fixed Rate Mortgage Notes Payable	Dec. 31, 2010 Fixed Rate Mortgage Notes Payable	Dec. 31, 2011 Variable Rate Mortgage Notes Payable and Credit Facility	Dec. 31, 2010 Variable Rate Mortgage Notes Payable and Credit Facility
Debt Instrument [Line Items]
Repayments of mortgage notes payable		$ 200,166,000	$ 69,327,000	$ 65,229,000			$ 28,785,000				$ 93,440,000
Variable rate unsecured cancelled credit facility																1,000,000,000
Repayments of fixed rate secured mortgage note												7,191,000		54,584,000	94,572,000
Mortgage notes assumed								55,400,000		44,044,000
Mortgage notes relinquished									55,800,000
Stated interest rate, percentage								5.24%	5.86%	4.75%		7.25%		5.88%	4.95%
Debt, maturity date					2012-05	2066-07				2015-08		2011-10		2019-01	2013-04	2011-11
Line of credit facility, term																4 years
Loss on extinguishment of debt, net		(1,940,000)		(25,910,000)										1,940,000	3,880,000
Line of credit facility, extension option																1 year
Repayment of unsecured notes	189,900,000	189,900,000	89,576,000	868,564,000
Interest rate on unsecured notes													6.67%
Unsecured credit facility, borrowing capacity																750,000,000
Unsecured credit facility, potential borrowing capacity																1,300,000,000
Line of credit facility, description																In September 2011, the Company entered into the Credit Facility, which has an available borrowing capacity of $750,000,000 and a 4-year term, plus a one year extension option.
Annual facility fee related to variable rate credit facility																1,313,000
Unsecured credit facility borrowing capacity subject to interest rate bid																				487,500,000
Outstanding balance of letters of credit																	52,659,000	51,235,000
Debt instrument, basis spread on variable rate					0.25%	0.45%										1.075%			1.00%	1.85%
Current interest rate																	1.37%
Net carrying value of apartment communities and improved land parcels securing debt		1,650,878,000
Guaranteed mortgage notes payable		$ 207,500,000
Weighted average interest rate, debt																					5.70%	5.70%	2.30%	2.20%
Debt instrument redemption description		The Company’s unsecured notes are redeemable at our option, in whole or in part, generally at a redemption price equal to the greater of (i) 100% of their principal amount or (ii) the sum of the present value of the remaining scheduled payments of principal and interest discounted at a rate equal to the yield on U.S. Treasury securities with a comparable maturity plus a spread between 25 and 45 basis points depending on the specific unsecured note, plus accrued and unpaid interest to the redemption date.
Redemption price, percentage		100.00%