Real Estate Investments (Details) (USD $)	3 Months Ended			12 Months Ended			3 Months Ended					3 Months Ended			1 Months Ended	3 Months Ended						1 Months Ended	12 Months Ended																									12 Months Ended	3 Months Ended							3 Months Ended	12 Months Ended					3 Months Ended					3 Months Ended	12 Months Ended			3 Months Ended					12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2011 Mortgages [Member] Wesco I - Arbos Parc Rose mortgage loan [Member]	Sep. 30, 2011 Mortgages [Member] Wesco I - Reveal mortgage loan [Member]	Sep. 30, 2011 Mortgages [Member] Wesco I - Redmond Hill mortgage loan [Member]	Dec. 31, 2011 Mortgages [Member] Wesco I - Briarwood mortgage loan [Member]	Dec. 31, 2011 Mortgages [Member] Wesco I - The Woods mortgage loan [Member]	Sep. 30, 2011 Mortgages [Member] Fountain at La Brea - bond financing [Member]	Dec. 31, 2011 Mortgages [Member] Santa Monica at La Brea - bond financing [Member]	Jun. 30, 2011 Line of Credit [Member] Wesco I - Arbos Parc Rose line of credit [Member]	Dec. 31, 2010 Construction Loans [Member] Queen Anne - construction loan [Member]	Mar. 31, 2011 Santee Village [Member]	Mar. 31, 2011 1000 Kiely [Member]	Jun. 30, 2011 Bellerive [Member]	Jun. 30, 2011 Santa Clara Retail [Member]	Sep. 30, 2011 Bernard [Member]	Dec. 31, 2011 Delano [Member]	Jan. 31, 2012 Bon Terra [Member]	Dec. 31, 2010 416 on Broadway [Member]	Dec. 31, 2010 Anavia [Member]	Dec. 31, 2010 Santee Court [Member]	Dec. 31, 2010 Courtyard off Main [Member]	Dec. 31, 2010 Corbella at Juanita Bay [Member]	Dec. 31, 2010 Allegro [Member]	Dec. 31, 2010 101 San Fernando [Member]	Dec. 31, 2010 The Commons [Member]	Dec. 31, 2010 Bella Villagio [Member]	Dec. 31, 2010 Muse [Member]	Dec. 31, 2010 Elevation [Member]	Dec. 31, 2011 Real Estate Under Development Activities [Member]	Dec. 31, 2011 Predevelopment Pipeline [Member]	Dec. 31, 2011 Predevelopment Pipeline - Land [Member]	Dec. 31, 2011 Equity Method Investment [Member]	Dec. 31, 2010 Equity Method Investment [Member]	Dec. 31, 2009 Equity Method Investment [Member]	Dec. 31, 2011 Cost Method Investment [Member] Series Preferred Stock [Member]	Dec. 31, 2010 Cost Method Investment [Member] Series Preferred Stock [Member]	Dec. 31, 2011 Equity Method Investment - Operating [Member]	Dec. 31, 2010 Equity Method Investment - Operating [Member]	Dec. 31, 2011 Equity Method Investment - Development [Member]	Dec. 31, 2010 Equity Method Investment - Development [Member]	Dec. 31, 2011 Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2010 Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2011 Wesco I LLC [Member] Equity Method Investment [Member]	Jun. 30, 2011 Wesco I - Arbors Parc Rose [Member] Equity Method Investment [Member]	Sep. 30, 2011 Wesco I - Reveal [Member] Equity Method Investment [Member]	Sep. 30, 2011 Wesco I - Redmond Hill [Member] Equity Method Investment [Member]	Dec. 31, 2011 Wesco I - Briarwood [Member] Equity Method Investment [Member]	Dec. 31, 2011 Wesco I - The Woods [Member] Equity Method Investment [Member]	Dec. 31, 2011 Essex Apartment Value Fund II, L.P. Fund II [Member] Equity Method Investment [Member]	Dec. 31, 2010 Essex Apartment Value Fund II, L.P. Fund II [Member] Equity Method Investment [Member]	Mar. 31, 2010 Essex Skyline at MacArthur Place [Member] Equity Method Investment [Member]	Dec. 31, 2010 Essex Skyline at MacArthur Place [Member] Equity Method Investment [Member]	Dec. 31, 2011 Essex Skyline at MacArthur Place [Member] Equity Method Investment - Operating [Member]	Dec. 31, 2010 Essex Skyline at MacArthur Place [Member] Equity Method Investment - Operating [Member]	Jun. 30, 2011 Canada Pension Plan Investment Board (CPPIB) I [Member] Equity Method Investment [Member]	Sep. 30, 2011 Canada Pension Plan Investment Board (CPPIB) II [Member] Equity Method Investment [Member]	Sep. 30, 2011 Fountain at La Brea [Member] Equity Method Investment [Member]	Dec. 31, 2011 Santa Monica at La Brea [Member] Equity Method Investment [Member]	Dec. 31, 2010 Queen Anne [Member] Equity Method Investment [Member]	Dec. 31, 2011 Queen Anne [Member] Equity Method Investment - Development [Member]	Dec. 31, 2010 Queen Anne [Member] Equity Method Investment - Development [Member]	Dec. 31, 2011 Wesco II, LLC [Member] Equity Method Investment [Member]	Dec. 31, 2011 Wesco II, LLC [Member] Equity Method Investment [Member]	Dec. 31, 2011 Wesco II, LLC [Member] Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2010 Wesco II, LLC [Member] Equity Method Investment - Preferred Interest [Member]	Jun. 30, 2011 Los Angeles I [Member] Equity Method Investment [Member]	Mar. 31, 2011 Los Angeles II [Member] Equity Method Investment [Member]	Sep. 30, 2010 Anaheim [Member] Equity Method Investment [Member]	Sep. 30, 2011 MyNewPlace.com [Member] Equity Method Investment [Member]	Mar. 31, 2009 Development joint venture [Member] Equity Method Investment [Member]	Dec. 31, 2011 Development joint venture [Member] Equity Method Investment [Member]	Dec. 31, 2011 Limited partnership interest in Essex Apartment Value Fund II LP [Member] Equity Method Investment - Operating [Member]	Dec. 31, 2010 Limited partnership interest in Essex Apartment Value Fund II LP [Member] Equity Method Investment - Operating [Member]	Dec. 31, 2011 Limited liability companies that own own and are developing Cadence and West Dublin [Member] Equity Method Investment - Development [Member]	Dec. 31, 2010 Limited liability companies that own own and are developing Cadence and West Dublin [Member] Equity Method Investment - Development [Member]	Dec. 31, 2011 Limited liability companies that own own and are developing Fountain and Santa Monica at La Brea [Member] Equity Method Investment - Development [Member]	Dec. 31, 2010 Limited liability companies that own own and are developing Fountain and Santa Monica at La Brea [Member] Equity Method Investment - Development [Member]	Dec. 31, 2011 Apartment communities in downtown Los Angeles [Member] Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2010 Apartment communities in downtown Los Angeles [Member] Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2011 Madison Park at Anaheim [Member] Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2010 Madison Park at Anaheim [Member] Equity Method Investment - Preferred Interest [Member]	Dec. 31, 2011 Membership interest in Wesco [Member] Equity Method Investment - Operating [Member]	Dec. 31, 2010 Membership interest in Wesco [Member] Equity Method Investment - Operating [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Number of communities acquired				5	11																																														4
Gain from sale of real estate	$ 3,200,000	$ 200,000	$ 5,200,000	$ 8,400,000																																																																						$ 900,000
Number of units sold			159
Ownership interest in joint venture (in hundredths)																																																						28.20%		50.00%				55.00%	55.00%	50.00%		50.00%
Fee earned for acquisition of property																																																								500,000
Number of institutional investors in partnership																																																						8
Equity investment, contributions by institutional investors																																																						265,900,000
Equity investment, contribution by Company																																																						75,000,000								9,000,000	5,800,000												5,800,000
Debt ratio as leverage (in hundredths)																																																						55.00%													60.00%	60.00%
Number of apartment communities owned	159			159																															1													6						14	14
Write-off of investment in joint venture development project				0	2,302,000	13,084,000																																																																					5,800,000
Ownership split in joint venture																																																50/50															50/50				50/50	50/50
Total equity commitment from partners																																																200,000,000
Each partner's equity commitment																																																100,900,000
Co-investment	383,412,000			383,412,000	107,840,000																																			0	639,000	163,945,000	95,187,000	96,072,000	0	123,395,000	12,014,000	78,300,000										24,063,000	29,187,000						17,981,000	0	175,000,000	175,000,000	88,075,000	0	13,000,000	9,700,000	12,000,000				64,294,000	66,000,000	62,897,000	0	15,194,000	0	22,792,000	0	12,528,000	12,014,000	75,588,000	0
Number of units to be developed by joint venture																																			481																										309	187	184	275
Square footage of real estate property (in sq ft)																																																														18,200	12,750
Ownership interest in joint venture by partner (in hundredths)																																																																50.00%
Stated term of preferred equity investment (in years)																																																																			7Y				5Y	10Y
Preferred return on preferred equity investment (in hundredths)																																																																			101.00%				10.00%
Preferred return on preferred equity investment in first five years (in hundredths)																																																																								9.00%	13.00%
Preferred return on preferred equity investment, thereafter, minimum (in hundredths)																																																																								10.00%
Preferred return on preferred equity investment, thereafter, maximum (in hundredths)																																																																								12.50%
Preferred return on preferred equity investment, thereafter (in hundredths)																																																																									15.00%
Net proceeds from sale of property																																																																										1,600,000
Income tax benefit recognized for 2009 write-off of investment in development joint venture																																																																												1,600,000
Balance sheets [Abstract]
Rental properties and real estate under development																																					1,483,596,000	750,808,000
Other assets																																					63,131,000	15,864,000
Total assets																																					1,546,727,000	766,672,000
Debt							(59,900,000)	(78,700,000)	(97,100,000)	(19,300,000)	(13,500,000)	(54,500,000)	(59,900,000)		(45,000,000)																						900,095,000	450,693,000																													(450,000,000)	(450,000,000)
Other liabilities																																					48,472,000	7,076,000
Equity																																					598,160,000	308,903,000
Total liabilities and partners' equity																																					1,546,727,000	766,672,000
Company's share of equity																																					383,412,000	107,201,000
Statements of operations [Abstract]
Property revenues																																					106,386,000	54,699,000	47,201,000
Property operating expenses																																					(43,065,000)	(24,098,000)	(18,450,000)
Net operating income																																					63,321,000	30,601,000	28,751,000
Interest expense																																					(27,843,000)	(13,619,000)	(10,805,000)
General and administrative																																					(1,528,000)	(709,000)	(294,000)
Depreciation and amortization																																					(44,412,000)	(20,850,000)	(15,656,000)
Net (loss) income																																					(10,462,000)	(4,577,000)	1,996,000
Company's share of net (loss) income																																					(467,000)	(1,715,000)	670,000
Projected debt service coverage ratio (in hundredths)																																																																				110.00%
Number of years the investment can not be repaid (in years)																																																																				2
Business Combination, Separately Recognized Transactions [Line Items]
Cost of acquired entity	103,300,000			103,300,000	456,250,000											17,000,000	31,400,000	27,000,000	20,600,000	13,800,000	14,100,000	16,000,000	43,000,000	80,600,000	31,100,000	30,000,000	23,400,000	29,850,000	64,100,000	42,500,000	54,000,000	39,100,000	18,600,000		42,800,000	44,300,000												429,200,000	92,000,000	132,900,000	151,300,000	27,800,000	25,200,000			128,000,000
Number of units acquired				386	2,032											73	121	63		63	66	60	115	250	165	110	169	97	323	264	231	152	156	1,235	481	298												2,013	373	438	882	160	160				349										3,221						768
Mortgage loan on property acquired, maturity date												Oct. 31, 2046	Dec. 31, 2046						Apr. 30, 2014																																		Sep. 30, 2016
Mortgage loan on property acquired, interest rate (in hundredths)																			5.00%																														4.70%		4.06%	3.93%	6.04%														3.83%
Number of units expected to be entitled																			494
Percentage of space leased (in hundredths)																			100.00%
Purchase price	103,300,000			103,300,000	456,250,000											17,000,000	31,400,000	27,000,000	20,600,000	13,800,000	14,100,000	16,000,000	43,000,000	80,600,000	31,100,000	30,000,000	23,400,000	29,850,000	64,100,000	42,500,000	54,000,000	39,100,000	18,600,000		42,800,000	44,300,000												429,200,000	92,000,000	132,900,000	151,300,000	27,800,000	25,200,000			128,000,000
Units				386	2,032											73	121	63		63	66	60	115	250	165	110	169	97	323	264	231	152	156	1,235	481	298												2,013	373	438	882	160	160				349										3,221						768
Quarter acquired																							Q4 2010	Q4 2010	Q4 2010	Q4 2010	Q4 2010	Q4 2010	Q3 2010	Q3 2010	Q3 2010	Q3 2010	Q2 2010
Sales price of real estate	7,400,000	1,400,000	16,000,000	23,400,000
Number of active development projects	5			5																														5
Estimated costs to be expended																																		282,600,000
Estimated cost of active development projects																																		422,600,000
Cost related to land held for future development or sale																																				44,300,000
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	440,000,000			440,000,000	207,200,000									100,000,000
Debt instrument, description of variable rate basis								LIBOR						LIBOR	LIBOR
Debt instrument, basis spread on variable rate (in hundredths)								1.90%						2.30%	1.95%
Secured mortgage loans on real estate							59,900,000	78,700,000	97,100,000	19,300,000	13,500,000	54,500,000	59,900,000		45,000,000																						(900,095,000)	(450,693,000)																													450,000,000	450,000,000
Debt instrument, maturity term (in years)							10Y	2Y	10Y	10Y
Debt instrument, number of extensions								2							2
Debt instrument, term of extensions (in years)								1Y
Number of loans on real estate acquired									2
Estimated total cost of renovation										$ 5,900,000
Interest rate swap, termination date		Sep. 30, 2016													Jul. 31, 2014
Interest rate swap, description of variable interest rate basis	SIFMA	SIFMA
Interest rate swap, basis spread on variable rate (in hundredths)	1.50%	1.50%		1.50%