Detail of Real Estate and Associated Funding Underlying the Company's Unconsolidated Investments (Detail) (USD $)					6 Months Ended								6 Months Ended																																										6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Unconsolidated Real Estate Investments Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Other Operating Joint Ventures Avalon Chrystie Place I - New York, NY Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Other Operating Joint Ventures Avalon at Mission Bay North II - San Francisco, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Other Operating Joint Ventures Avalon Del Rey - Los Angeles, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Centerpoint - Baltimore, MD MortgageLoan Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon at Redondo Beach - Los Angeles, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Lakeside - Chicago, IL Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Columbia - Baltimore, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Sunset - Los Angeles, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon at Poplar Creek - Chicago, IL Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon at Civic Center - Norwalk, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Paseo Place - Fremont, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon at Yerba Buena - San Francisco, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon at Aberdeen Station - Aberdeen, NJ Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I The Springs - Corona, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Lombard - Lombard, IL Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Cedar Place - Columbia, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Middlesex Crossing - Billerica, MA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Crystal Hill - Ponoma, NY Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Skyway - San Jose, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Avalon Rutherford Station - East Rutherford, NJ Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I South Hills Apartments - West Covina, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund I Weymouth Place - Weymouth, MA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Other Development Joint Ventures Aria at Hathorne - Danvers, MA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Fox Run Apartments - Plainsboro, NJ MortgageLoan Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Avalon Bellevue Park - Bellevue, WA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Avalon Fair Oaks - Fairfax, VA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Avalon Rothbury - Gaithersburg, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II The Apartments at Briarwood - Owings Mills, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Grove Park Apartments - Gaithersburg, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Creekside Meadows - Tustin, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Canyonwoods - Lake Forest, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Waterstone Carlsbad - Carlsbad, CA Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Yale Village - Rockville, MD Home		Jun. 30, 2011 Unconsolidated Real Estate Investments Fund II Corporate debt		Jun. 30, 2011 Unconsolidated Real Estate Investments Total Other Joint Ventures Home
Investment Holdings [Line Items]
Company Ownership Percentage					20.00%	[1]	25.00%	[2]	30.00%		15.20%																																								50.00%	[2],[3],[4]	31.30%
# of Apartment Homes			9,024		361	[1]	313	[2]	309		3,829		392	[5]	105		204		170		82		196		192		134		160		290		320	[6]	256		156		252		168		348		108		85		211		64	[2],[3],[4]	4,148		776	[7]	220		491		203		348		684		628		140		448		210				1,047
Total Capitalized Cost	$ 8,331,037,000	$ 8,148,939,000	$ 1,681,949,000	[8]	$ 136,544,000	[1],[8]	$ 124,031,000	[2],[8]	$ 70,053,000	[8]	$ 726,878,000	[8]	$ 80,259,000	[5],[8]	$ 24,624,000	[8]	$ 18,491,000	[8]	$ 29,410,000	[8]	$ 20,903,000	[8]	$ 28,097,000	[8]	$ 42,756,000	[8]	$ 25,078,000	[8]	$ 66,813,000	[8]	$ 58,587,000	[8]	$ 29,875,000	[6],[8]	$ 35,323,000	[8]	$ 24,505,000	[8]	$ 38,386,000	[8]	$ 38,645,000	[8]	$ 78,251,000	[8]	$ 36,821,000	[8]	$ 24,756,000	[8]	$ 25,298,000	[8]			$ 624,443,000	[8]	$ 86,727,000	[7],[8]	$ 33,993,000	[8]	$ 72,100,000	[8]	$ 31,481,000	[8]	$ 45,125,000	[8]	$ 101,899,000	[8]	$ 99,793,000	[8]	$ 25,316,000	[8]	$ 78,509,000	[8]	$ 49,500,000	[8]			$ 330,628,000	[8]
Debt Amount			$ 1,096,377,000	[9]	$ 117,000,000	[1],[9]	$ 105,000,000	[2],[9]	$ 44,692,000	[9]	$ 433,660,000	[9]	$ 45,000,000	[5],[9]	$ 21,033,000	[9]	$ 12,056,000	[9]	$ 22,275,000	[9]	$ 12,750,000	[9]	$ 16,500,000	[9]	$ 27,001,000	[9]	$ 11,800,000	[9]	$ 41,500,000	[9]	$ 39,842,000	[9]	$ 23,717,000	[6],[9]	$ 17,243,000	[9]	$ 12,000,000	[9]	$ 24,100,000	[9]	$ 24,500,000	[9]	$ 37,500,000	[9]	$ 19,627,000	[9]	$ 11,761,000	[9]	$ 13,455,000	[9]	$ 1,860,000	[2],[3],[4],[9]	$ 394,165,000	[9]	$ 54,509,000	[7],[9]	$ 21,515,000	[9]	$ 42,600,000	[9]	$ 18,750,000	[9]	$ 26,850,000	[9]	$ 63,200,000	[9]	$ 59,100,000	[9]			$ 46,141,000	[9]			$ 61,500,000	[9]	$ 268,552,000	[9]
Debt Interest Rate			4.60%	[10]	0.81%	[1],[10]	6.02%	[10],[2]	3.53%	[10]	5.60%	[10]	5.74%	[10],[5]	4.87%	[10]	5.74%	[10]	5.48%	[10]	5.41%	[10]	4.83%	[10]	5.38%	[10]	5.74%	[10]	5.88%	[10]	5.64%	[10]	6.06%	[10],[6]	5.43%	[10]	5.68%	[10]	5.49%	[10]	5.43%	[10]	6.11%	[10]	6.13%	[10]	5.92%	[10]	5.12%	[10]	7.98%	[10],[2],[3],[4]	4.30%	[10]	4.56%	[10],[7]	5.52%	[10]	5.26%	[10]	2.78%	[10]	3.64%	[10]	5.42%	[10]	3.81%	[10]			4.68%	[10]			2.69%	[10]	3.30%	[10]
Debt Type					Variable	[1]	Fixed	[2]	Variable				Fixed	[5]	Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed	[6]	Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Fixed		Variable	[2],[3],[4]			Fixed	[7]	Fixed		Fixed		Variable		Fixed		Fixed		Fixed		N/A		Fixed		N/A		Variable
Debt Maturity Date					Nov 2036	[1]	Dec 2015	[2]	Apr 2016				Dec 2014	[5]	Oct 2011		Mar 2012		Apr 2013		Mar 2014		Oct 2013		Aug 2013		Nov 2014		Mar 2014		Sep 2013		Oct 2014	[6]	Jan 2014		Feb 2015		Dec 2014		Dec 2014		Mar 2014		Sep 2016		Oct 2014		Mar 2015		Jun 2010	[2],[3],[4]			Nov 2014	[7]	Jun 2019		May 2017		Jun 2017		Nov 2017		Jan 2018		Oct 2017		N/A		Feb 2018		N/A		Dec 2011

[1] After the venture makes certain threshold distributions to the third-party partner, the Company generally receives 50% of all further distributions.

[2] The Company has contributed land, receiving capital credit for the fair value upon contribution, as its only capital contribution to this development.

[3] After the venture makes certain threshold distributions to the Company, the Company receives 50% of all further distributions.

[4] The loan for this venture matured in June 2010. As of June 30, 2011, the amounts under this borrowing have not been repaid, and the venture is negotiating an extension or refinancing of the amounts outstanding. As of June 30, 2011, the lender has declared an event of default with respect to the note and required the venture to pay a default rate of interest, the impact of 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.

[5] Borrowing on this community is comprised of three mortgage loans.

[6] Beginning in the third quarter of 2010, the Company consolidated the net assets and results of operations of The Springs.

[7] Borrowing on this community is comprised of two mortgage loans.

[8] Represents total capitalized cost as of June 30, 2011.

[9] 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.

[10] Represents weighted average rate on outstanding debt as of June 30, 2011.