Notes Payable, Unsecured Notes and Credit Facility (Details) (USD $)									3 Months Ended			3 Months Ended						3 Months Ended					3 Months Ended											1 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Archstone Enterprise LP	Feb. 27, 2013 Archstone Enterprise LP	Mar. 31, 2013 Unsecured notes	Dec. 31, 2012 Unsecured notes	Mar. 31, 2013 Mortgage notes payable	Dec. 31, 2012 Mortgage notes payable	Mar. 31, 2013 Tax-exempt bonds and conventional loans	Mar. 31, 2013 Tax-exempt bonds	Mar. 31, 2013 Fixed Rate Tax-exempt bonds Archstone Meadowbrook Crossing	Mar. 31, 2013 Variable Rate Tax-exempt bonds Archstone Clinton North/South SIFMA	Mar. 31, 2013 Variable Rate Tax-exempt bonds Archstone Midtown West SIFMA	Mar. 31, 2013 Variable Rate Tax-exempt bonds Archstone San Bruno SIFMA	Mar. 31, 2013 Variable Rate Tax-exempt bonds Archstone Calabasas SIFMA	Mar. 31, 2013 Fixed Rate Conventional loans	Mar. 31, 2013 Fixed Rate Conventional loans Archstone Meadowbrook Crossing	Mar. 31, 2013 Fixed Rate Conventional loans Fannie Mae Pool 6	Mar. 31, 2013 Fixed Rate Conventional loans Fannie Mae Pool 2	Mar. 31, 2013 Fixed Rate Conventional loans Archstone First + M	Mar. 31, 2013 Fixed Rate Conventional loans Archstone San Bruno II	Mar. 31, 2013 Fixed Rate Conventional loans Archstone Lexington	Mar. 31, 2013 Variable Rate Conventional loans	Mar. 31, 2013 Variable Rate Conventional loans Archstone Calabasas DMBS	Mar. 31, 2013 Variable Rate Conventional loans Fannie Mae Pool 9 LIBOR	Mar. 31, 2013 Variable Rate Conventional loans Freddie Mac Pool LIBOR	Mar. 31, 2013 Variable Rate Conventional loans Archstone South San Francisco DMBS	Mar. 31, 2013 Variable Rate Conventional loans Archstone Wheaton Station DMBS	Mar. 31, 2013 Variable Rate Conventional loans Archstone San Bruno III LIBOR	Mar. 31, 2013 Variable Rate Conventional loans Archstone La Mesa DMBS	Mar. 31, 2013 Variable Rate Conventional loans Archstone Parkland Gardens LIBOR	Mar. 31, 2013 Variable Rate Conventional loans Archstone Toscano LIBOR	Mar. 31, 2013 Variable Rate Conventional loans Archstone Memorial Heights LIBOR	Mar. 31, 2013 4.95% medium term notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes					$ 1,850,000,000	$ 1,950,000,000	$ 2,875,541,000	$ 1,427,133,000
Variable rate notes							1,058,967,000	476,935,000
Total notes payable and unsecured notes	5,784,508,000	3,854,068,000			1,850,000,000		3,700,885,000
Total mortgage notes payable, unsecured notes and Credit Facility	5,784,508,000	3,854,068,000
Amount of debt discount	4,039,000	4,202,000
Amount of debt premium	147,820,000	1,167,000
Assumed principal amount of indebtedness	3,512,202,000		3,512,202,000	3,512,202,000					3,512,202,000	540,060,000	62,200,000	268,500,000	100,500,000	64,450,000	44,410,000	1,832,950,000	22,325,000	940,923,000	692,192,000	128,826,000	31,700,000	16,984,000	1,139,192,000	57,472,000	636,756,000	184,483,000	76,706,000	44,539,000	47,000,000	24,755,000	18,176,000	42,805,000	6,500,000
Repayment of debt									1,477,720,000							443,000,000		443,000,000					1,034,720,000		636,756,000	184,483,000	76,706,000	44,539,000		24,755,000	18,176,000	42,805,000	6,500,000	100,000,000
Debt fair value exceeds the principal face value	150,298,000			220,777,000
Debt instrument variable rate												SIFMA	SIFMA	SIFMA	SIFMA									DMBS	LIBOR	LIBOR	DMBS	DMBS	LIBOR	DMBS	LIBOR	LIBOR	LIBOR
Stated interest rate (as a percent)											4.61%	1.53%	1.13%	1.35%	1.48%		4.81%	6.19%	6.26%	5.60%	5.37%	5.55%		1.44%	1.27%	0.96%	1.00%	1.00%	2.60%	1.00%	2.25%	6.00%	2.50%	4.95%
Net Principal Balance Assumed				$ 2,034,482,000					$ 2,034,482,000	$ 540,060,000	$ 62,200,000	$ 268,500,000	$ 100,500,000	$ 64,450,000	$ 44,410,000	$ 1,389,950,000	$ 22,325,000	$ 497,923,000	$ 692,192,000	$ 128,826,000	$ 31,700,000	$ 16,984,000	$ 104,472,000	$ 57,472,000					$ 47,000,000