Equity (Details) (USD $)	1 Months Ended				3 Months Ended		9 Months Ended			1 Months Ended
	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Sep. 30, 2011 lease Property series tenant LLC	Sep. 30, 2010	Sep. 30, 2011 segment Property lease series tenant LLC	Sep. 30, 2010	Dec. 31, 2010	Oct. 31, 2011 Series E cumulative redeemable preferred stock	Jul. 31, 2011 Series E cumulative redeemable preferred stock	Apr. 30, 2011 Series E cumulative redeemable preferred stock	Jan. 31, 2011 Series E cumulative redeemable preferred stock	Oct. 31, 2011 Series F cumulative redeemable preferred stock	Jul. 31, 2011 Series F cumulative redeemable preferred stock	Apr. 30, 2011 Series F cumulative redeemable preferred stock	Jan. 31, 2011 Series F cumulative redeemable preferred stock	Dec. 31, 2010 Public offering transaction December 2010	Mar. 31, 2011 Public offering completed in March 2011
Class of Stock
Number of series of preferred stock outstanding					2		2
Dividends declared per preferred share (in dollars per share)										$ 0.45313	$ 0.45313	$ 0.45313	$ 0.45313	$ 0.44375	$ 0.44375	$ 0.44375	$ 0.44375
Dividends declared per common share (in dollars per share)	$ 0.48	$ 0.48	$ 0.48	$ 0.48	$ 0.48	$ 0.465	$ 1.44	$ 1.395
Issuance of common stock, net							$ 1,288,332,000	$ 519,584,000										$ 1,472,000,000	$ 1,273,000,000
Issuance of common stock, net (in shares)																		46,000,000	34,500,000
Stock issued under new issues (in dollars per share)																		$ 32.00	$ 36.90
Proceeds from issuance of common stock																		1,413,000,000	1,235,000,000
Company's common stock issuances
Dividend Reinvestment and Stock Purchase Plan ("DRIP") (in shares)							1,533,000	869,000
Conversion of DownREIT units (in shares)							30,000	130,000
Exercise of stock options (in shares)							733,000	150,000
Restricted stock awards ("RSA") (in shares)								221,000
Vesting of restricted stock units (in shares)							228,000	265,000
Accumulated other comprehensive loss
Unrealized losses on available for sale securities					(10,152,000)		(10,152,000)
Unrealized losses on cash flow hedges, net					(15,526,000)		(15,526,000)		(10,312,000)
Supplemental Executive Retirement Plan minimum liability					(2,199,000)		(2,199,000)		(2,299,000)
Cumulative foreign currency translation adjustment					(606,000)		(606,000)		(626,000)
Total accumulated other comprehensive loss					(28,483,000)		(28,483,000)		(13,237,000)
Noncontrolling interests
Non-managing member units outstanding in DownREIT LLCs (in units)					4,200,000		4,200,000
Number of DownREIT LLCs having non-managing member units outstanding					5		5
Non-managing member unitholders					171,091,000		171,091,000		173,745,000
Non-managing member units outstanding, fair value					208,000,000		208,000,000
Reconciliation of comprehensive income (loss)
Net income					175,471,000	26,173,000	483,707,000	198,869,000
Other comprehensive loss					(14,650,000)	(2,874,000)	(15,246,000)	(5,292,000)
Total comprehensive income					$ 160,821,000	$ 23,299,000	$ 468,461,000	$ 193,577,000