Co-Investments (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	$ 275,410		$ 275,410		$ 107,840
Statements of operations [Abstract]
Company's share of net income (loss)	317	(626)	(330)	(1,027)
Equity Method Investment [Member]
Balance sheets [Abstract]
Rental properties and real estate under development	1,405,295		1,405,295		750,808
Other assets	58,806		58,806		15,864
Total assets	1,464,101		1,464,101		766,672
Mortgage notes	886,632		886,632		450,693
Other liabilities	56,050		56,050		7,076
Equity	521,419		521,419		308,903
Total liabilities and equity	1,464,101		1,464,101		766,672
Company's share of equity	275,410		275,410		107,201
Statements of operations [Abstract]
Property revenues	28,286	13,824	70,882	38,634
Property operating expenses	(11,699)	(6,513)	(29,394)	(17,176)
Net property operating income	16,587	7,311	41,488	21,458
Interest expense	(7,354)	(3,262)	(22,764)	(9,174)
General and administrative	(82)	0	(1,104)	0
Depreciation and amortization	(11,957)	(5,419)	(29,963)	(14,628)
Net loss	(2,806)	(1,370)	(12,343)	(2,344)
Company's share of operating income (loss)	(602)	(626)	(1,249)	(1,027)
Company's preferred interest/gain - Multifamily Technology Solutions, Inc.	919	0	919	0
Company's share of net income (loss)	317	(626)	(330)	(1,027)
Equity Method Investment [Member] | Limited partnership interest in Essex Apartment Value Fund II LP [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	64,505		64,505		66,000
Equity Method Investment [Member] | Fountain at La Brea [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	9,186		9,186		0
Equity Method Investment [Member] | Subtotal of development co-investments [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	94,554		94,554		0
Equity Method Investment [Member] | Wesco I LLC [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	55,444		55,444		0
Equity Method Investment [Member] | Cadence and West Dublin [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	68,368		68,368		0
Equity Method Investment [Member] | Essex Skyline at MacArthur Place [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	25,781		25,781		29,187
Equity Method Investment [Member] | Apartment communities in downtown Los Angeles [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	22,792		22,792		0
Equity Method Investment [Member] | Queen Anne [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	17,000		17,000		0
Equity Method Investment [Member] | Madison Park at Anaheim [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	12,334		12,334		12,014
Equity Method Investment [Member] | Subtotal of preferred interest co-investments [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	35,126		35,126		12,014
Equity Method Investment [Member] | Subtotal of operating co-investments [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	145,730		145,730		95,187
Cost Method Investment [Member] | Series A Preferred Stock interest in Multifamily Technology Solutions Inc [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Co-investment	$ 0		$ 0		$ 639