Organization and Basis of Presentation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Organization and Basis of Presentation [Abstract]
General partnership interest (in hundredths)			93.40%
Operating Partnership units outstanding (in shares)	2,228,730		2,228,730		2,200,907
Redemption value of operating partnership units outstanding	$ 301,500,000		$ 301,500,000		$ 251,400,000
Numbers of apartment communities owned	149		149
Aggregate apartment units owned (in units)	30,557		30,557
Ownership interests, number of commercial buildings	6		6
Ownership interests, number of active development projects	6		6
Fund Activities
Fund II's number of institutional investors	8		8
Total combined partnership's equity in Essex Apartment Value Fund II, L.P. ( Fund II)	265,900,000		265,900,000
Capital contribution to Essex Apartment Value Fund II, L.P.	75,000,000		75,000,000
General partner and limited partner interest in Fund II (in hundredths)	28.20%		28.20%
Fund II utilized leverage equal to the initial acquisition of the underlying real estate (in hundredths)	55.00%		55.00%
Units of Apartments owned by Essex Apartment Value Fund II, L.P.	14		14
Programmatic joint venture participation level description	50/50		50/50
Programmatic joint venture total equity commitment	200,000,000		200,000,000
Programmatic joint venture total of each partner's equity commitment	100,000,000		100,000,000
Joint venture partner's leverage percentage - minimum (in hundredths)	50.00%		50.00%
Joint venture partner's leverage percentage - maximum (in hundredths)	60.00%		60.00%
Programmatic joint venture investment period (in years)	2		2
Variable Interest Entities
Number of DownREIT limited partnerships the company consolidates	19		19
Number of communities within the DownREIT partnership	12		12
Total DownREIT Partnership's Outstanding units (shares)	1,072,161		1,072,161		1,096,871
Redemption value of the variable interest entities	145,100,000		145,100,000		125,300,000
Assets related to variable interest entities, net intercompany eliminations	214,600,000		214,600,000		217,300,000
Liabilities related to variable interest entities, net of intercompany eliminations	170,000,000		170,000,000		168,000,000
Stock-Based Compensation
Stock-based compensation expense for options and restricted stock	400,000	300,000	700,000	500,000
Intrinsic value of the stock options exercised	2,000,000	500,000	3,000,000	1,500,000
Intrinsic value of the stock options outstanding and fully vested	10,900,000		10,900,000
Unrecognized compensation cost related to unvested share-based compensation granted under the stock option and restricted stock plans	4,100,000		4,100,000
Compensation cost recognized for stock options over a weighted-average period	1 to 6 years		1 to 6 years
Compensation cost for restricted stock awards expected to be recognized straight-line	7		7
Stock-based compensation expense for the Series Z Units	300,000	800,000	500,000	1,400,000
Series Z units converted into common units of the operating partnership			131,409
Capitalization of stock based compensation for Z units	100,000	200,000	200,000	400,000
Intrinsic value of Series Z Units outstanding	17,600,000		17,600,000
Total unrecognized compensation cost related to Z-1 Units subject to future vesting	6,500,000		6,500,000
Unamortized cost recognition period range (in years)	next year to fourteen years		next year to fourteen years
Fair Value of Financial Instruments
Fixed rate debt and unsecured bonds	1,790,000,000		1,790,000,000
Fair value of fixed rate debt and unsecured bonds	1,830,000,000		1,830,000,000
Variable rate debt instruments excluding borrowings under the lines of credit	256,800,000		256,800,000
Fair value of variable rate debt excluding borrowing under lines of credit	234,500,000		234,500,000
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	28,670,000		28,670,000		45,226,000
Unrealized Gain/(Loss)	2,687,000		2,687,000		5,097,000
Fair Value	31,357,000		31,357,000		50,323,000
Proceeds from sales of available for sale securities	0	22,500,000	26,800,000	64,700,000
Realized gain from sales of available for sale securities		4,000,000	4,500,000	9,000,000
Marketable securities	44,300,000		44,300,000
Investment-grade unsecured bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,608,000		3,608,000		22,243,000
Unrealized Gain/(Loss)	427,000		427,000		4,403,000
Fair Value	4,035,000		4,035,000		26,646,000
Investment funds-US treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,549,000		10,549,000		14,345,000
Unrealized Gain/(Loss)	164,000		164,000		582,000
Fair Value	10,713,000		10,713,000		14,927,000
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	14,513,000		14,513,000		8,638,000
Unrealized Gain/(Loss)	2,096,000		2,096,000		112,000
Fair Value	$ 16,609,000		$ 16,609,000		$ 8,750,000