Real Estate Investments (Details) (USD $)	3 Months Ended			12 Months Ended				3 Months Ended		12 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		12 Months Ended										3 Months Ended											12 Months Ended				12 Months Ended											3 Months Ended							12 Months Ended														1 Months Ended		3 Months Ended	12 Months Ended						12 Months Ended	3 Months Ended								12 Months Ended			3 Months Ended		12 Months Ended												3 Months Ended			3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended															3 Months Ended						12 Months Ended		12 Months Ended						3 Months Ended			12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2012 Huntington Beach [Member]	Sep. 30, 2012 Montebello [Member]	Sep. 30, 2012 Park West [Member]	Sep. 30, 2012 Domaine [Member]	Dec. 31, 2012 Wesco III [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]	Dec. 31, 2010 Construction Loans [Member] Expo (formerly Queen Anne) - construction loan [Member]	Dec. 31, 2012 Construction Loans [Member] Expo (formerly Queen Anne) - construction loan [Member]	Dec. 31, 2011 Construction Loans [Member] Expo (formerly Queen Anne) - construction loan [Member]	Dec. 31, 2012 Santee Village [Member]	Dec. 31, 2011 Santee Village [Member]	Dec. 31, 2012 1000 Kiely [Member]	Dec. 31, 2011 1000 Kiely [Member]	Dec. 31, 2012 Bellerive [Member]	Dec. 31, 2011 Bellerive [Member]	Dec. 31, 2012 Bernard [Member]	Dec. 31, 2011 Bernard [Member]	Dec. 31, 2012 Delano [Member]	Dec. 31, 2011 Delano [Member]	Mar. 31, 2012 Bon Terra [Member]	Mar. 31, 2012 Reed Square [Member]	Jun. 30, 2012 Essex Skyline at MacArthur Place [Member]	Jun. 30, 2012 Park Catalina [Member]	Jun. 30, 2012 Huntington Beach [Member]	Sep. 30, 2012 Montebello [Member]	Sep. 30, 2012 Park West [Member]	Sep. 30, 2012 Domaine [Member]	Dec. 31, 2012 Ascent [Member]	Dec. 31, 2012 Willow Lake Apartments [Member]	Dec. 31, 2012 Bennett Lofts [Member]	Dec. 31, 2012 Real Estate Under Development Activities [Member]	Dec. 31, 2012 Real Estate predevelopment projects [Member]	Dec. 31, 2012 Predevelopment Pipeline [Member]	Dec. 31, 2012 Predevelopment Pipeline - Land [Member]	Dec. 31, 2011 Wesco I LLC [Member]	Dec. 31, 2012 Wesco I Arbors Parc Rose [Member]	Dec. 31, 2011 Wesco I Arbors Parc Rose [Member]	Dec. 31, 2012 Wesco I Redmond Hill [Member]	Dec. 31, 2011 Wesco I Redmond Hill [Member]	Dec. 31, 2012 Wesco I Reveal [Member]	Dec. 31, 2011 Wesco I Reveal [Member]	Dec. 31, 2012 Wesco I Briarwood [Member]	Dec. 31, 2011 Wesco I Briarwood [Member]	Dec. 31, 2012 Wesco I The Woods [Member]	Dec. 31, 2011 Wesco I The Woods [Member]	Dec. 31, 2012 Wesco I Madrid [Member]	Dec. 31, 2012 Wesco I Pacific Electric Lofts [Member]	Jun. 30, 2012 Tierra Del Sol/Norte [Member]	Mar. 31, 2012 Alpine Country [Member]	Jun. 30, 2011 Woodlawn Colonial [Member]	Dec. 31, 2011 Clarendon Office Building in Woodland Hills [Member]	Dec. 31, 2012 Wesco III Haver Hill [Member]	Dec. 31, 2012 Parcwood [Member]	Dec. 31, 2011 Parcwood [Member]	Dec. 31, 2012 Regency Tower [Member]	Dec. 31, 2011 Regency Tower [Member]	Dec. 31, 2012 Studio 40-41 [Member]	Dec. 31, 2011 Studio 40-41 [Member]	Dec. 31, 2012 Tower @ 801 [Member]	Dec. 31, 2011 Tower @ 801 [Member]	Dec. 31, 2012 Cielo [Member]	Dec. 31, 2011 Cielo [Member]	Dec. 31, 2012 Echo Ridge [Member]	Dec. 31, 2011 Echo Ridge [Member]	Dec. 31, 2012 The Enclave [Member]	Dec. 31, 2011 The Enclave [Member]	Dec. 31, 2012 Willow Lake Apartments and Bennett Lofts [Member]	Jan. 31, 2013 Willow Lake Apartments and Bennett Lofts [Member]	Dec. 31, 2011 Equity Method Investment [Member]	Dec. 31, 2012 Equity Method Investment [Member]	Dec. 31, 2011 Equity Method Investment [Member]	Dec. 31, 2010 Equity Method Investment [Member]	Jun. 30, 2012 Equity Method Investment [Member]	Sep. 30, 2012 Equity Method Investment [Member] Wesco I Santa Clara [Member]	Dec. 31, 2011 Equity Method Investment [Member] Mortgages [Member] Wesco II, LLC [Member]	Dec. 31, 2012 Equity Method Investment [Member] Wesco I LLC [Member]	Sep. 30, 2012 Equity Method Investment [Member] Wesco I Santa Clara [Member]	Dec. 31, 2011 Equity Method Investment [Member] Wesco II LLC [Member]	Dec. 31, 2012 Equity Method Investment Operating [Member]	Dec. 31, 2011 Equity Method Investment Operating [Member]	Dec. 31, 2012 Equity Method Investment Development [Member]	Dec. 31, 2011 Equity Method Investment Development [Member]	Dec. 31, 2012 Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Equity Method Investment Preferred Interest [Member]	Dec. 31, 2012 Wesco I LLC [Member]	Dec. 31, 2011 Wesco I LLC [Member]	Dec. 31, 2012 Wesco I LLC [Member] Equity Method Investment [Member]	Dec. 31, 2012 Essex Apartment Value Fund II LP Fund II [Member]	Dec. 31, 2012 Essex Apartment Value Fund II LP Fund II [Member] Equity Method Investment [Member]	Dec. 31, 2012 Essex Skyline at MacArthur Place [Member]	Jun. 30, 2012 Essex Skyline at MacArthur Place [Member]	Dec. 31, 2012 Essex Skyline at MacArthur Place [Member] Equity Method Investment Operating [Member]	Dec. 31, 2011 Essex Skyline at MacArthur Place [Member] Equity Method Investment Operating [Member]	Dec. 31, 2012 Canada Pension Plan Investment Board (CPPIB) [Member]	Sep. 30, 2012 Fountain at La Brea [Member] Equity Method Investment [Member]	Sep. 30, 2011 Fountain at La Brea [Member] Equity Method Investment [Member] sqft	Dec. 31, 2012 Santa Monica at La Brea [Member] Equity Method Investment [Member] sqft	Dec. 31, 2011 Santa Monica at La Brea [Member] Equity Method Investment [Member]	Dec. 31, 2010 Expo formerly Queen Anne [Member] Equity Method Investment [Member]	Dec. 31, 2012 Expo formerly Queen Anne [Member] Equity Method Investment Development [Member]	Dec. 31, 2011 Expo formerly Queen Anne [Member] Equity Method Investment Development [Member]	Dec. 31, 2011 Wesco II LLC [Member] Equity Method Investment [Member]	Dec. 31, 2012 Wesco II LLC [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Wesco II LLC [Member] Equity Method Investment Preferred Interest [Member]	Jun. 30, 2011 Los Angeles I [Member] Equity Method Investment [Member]	Dec. 31, 2012 Los Angeles II [Member]	Dec. 31, 2011 Los Angeles II [Member]	Mar. 31, 2011 Los Angeles II [Member] Equity Method Investment [Member]	Dec. 31, 2012 Anaheim [Member]	Jun. 30, 2011 MyNewPlace com [Member] Equity Method Investment [Member]	Dec. 31, 2012 Limited partnership interest in Essex Apartment Value Fund II LP [Member] Equity Method Investment Operating [Member]	Dec. 31, 2011 Limited partnership interest in Essex Apartment Value Fund II LP [Member] Equity Method Investment Operating [Member]	Dec. 31, 2012 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 Limited liability companies that own own and are developing Fountain and Santa Monica at La Brea [Member] Equity Method Investment Development [Member]	Dec. 31, 2012 Limited liability companies that own and are developing Epic, Connoly Station, Elkhorn, and Folsom and Fifth [Member]L Equity Method Investment Development [Member]	Dec. 31, 2011 Limited liability companies that own and are developing Epic, Connoly Station, Elkhorn, and Folsom and Fifth [Member]L Equity Method Investment Development [Member]	Dec. 31, 2012 Apartment communities in downtown Los Angeles [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Apartment communities in downtown Los Angeles [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2012 Madison Park at Anaheim [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Madison Park at Anaheim [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2012 Membership interest in Wesco I [Member] Equity Method Investment Operating [Member]	Dec. 31, 2011 Membership interest in Wesco I [Member] Equity Method Investment Operating [Member]	Dec. 31, 2012 Membership interest in Wesco III [Member] Equity Method Investment Operating [Member]	Dec. 31, 2011 Membership interest in Wesco III [Member] Equity Method Investment Operating [Member]	Jun. 30, 2012 Tierra Del Sol/Norte [Member]	Mar. 31, 2012 Alpine Country [Member]	Jun. 30, 2011 Woodlawn Colonial [Member]	Sep. 30, 2011 View Pointe Land Parcel [Member]	Dec. 31, 2011 Clarendon Office Building in Woodland Hills [Member]	Dec. 31, 2012 Wesco I Pacific Electric Lofts [Member] sqft	Dec. 31, 2012 Wesco III [Member]	Dec. 31, 2012 Wesco III [Member] Equity Method Investment [Member]	Dec. 31, 2011 Parcwood [Member]	Dec. 31, 2011 Regency Tower [Member]	Dec. 31, 2011 Studio 40-41 [Member]	Dec. 31, 2011 Tower @ 801 [Member]	Dec. 31, 2011 Cielo [Member]	Dec. 31, 2012 Cupertino California [Member]	Jun. 30, 2012 Cupertino California [Member] Equity Method Investment [Member]	Dec. 31, 2012 Cupertino California [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Cupertino California [Member] Equity Method Investment Preferred Interest [Member]	Dec. 31, 2011 Echo Ridge [Member]	Dec. 31, 2011 The Enclave [Member]	Dec. 31, 2012 CPPIB Epic Phase I and II [Member]	Dec. 31, 2012 CPPIB Connolly Station [Member]	Dec. 31, 2012 CPPIB Folsom and Fifth [Member]	Dec. 31, 2012 CPPIB Elkhom [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Number of communities acquired				11	5																																																																																							5	9
Promote income	$ 2,300,000																																																																																															$ 2,300,000
Gain from sale of real estate				10,900,000																																																																																										106,000,000																						900,000															7,000,000	3,900,000	5,200,000	200,000	3,200,000
Number of units sold					1,688																																																																																																																														156	108	159						312	178	149	173	119					120	637
Ownership interest in joint venture (in hundredths)																																																																																															28.20%					55.00%					50.00%																																													55.00%	55.00%	55.00%	55.00%
Number of units in joint venture																																																																																																				1,538																																																		569	309	463	197
Estimated total cost																																																																																																				612,200,000																																																		191,600,000	94,500,000	250,000,000	76,100,000
Construction start																																																																																																																																																						Aug-11	Aug-11	Jun-12	Aug-12
Initial occupancy																																																																																																																																																						May-13	Aug-13	Apr-14	Jun-14
Prepayment penalties on debt obligation																																																																																														2,300,000
Pro rata gain on sale of property of joint venture																																																																																														29,100,000
Number of institutional investors in partnership																																																																																															8
Equity investment contributions by institutional investors																																																																																															265,900,000
Equity investment, contribution by Company																																																																																															75,000,000		85,000,000					9,000,000	5,800,000																																		10,000,000
Debt ratio as leverage (in hundredths)																																																																																															55.00%													60.00%																													50.00%
Number of apartment communities owned				163																																																																																										7						4														2
Ownership split in joint venture																																																																																													50/50										50/50					50/50																														50/50
Total equity commitment from partners																																																																																													300,000,000																																												120,000,000
Each partner's equity commitment																																																																																													150,000,000																																													60,000,000
Co-investment	21,900,000	383,412,000		571,345,000	383,412,000																																																																										14,000,000						207,416,000	163,945,000	221,666,000	96,072,000	142,263,000	123,395,000			150,000,000					0	24,063,000							18,752,000	17,981,000	175,000,000	91,843,000	88,075,000	13,000,000			9,700,000			53,601,000	64,294,000	16,552,000	15,194,000	186,362,000	62,897,000	22,807,000	22,792,000	13,175,000	12,528,000	143,874,000	75,588,000	9,941,000	0																14,438,000	0
Percentage debt in joint venture (in hundredths)																																																																																											50.00%																																														50.00%
Number of units to be developed by joint venture																																																																																																					187			184	275
Square footage of real estate property (in sq ft)																																																																																																						18,200	12,750																																	22,100
Ownership interest in joint venture by partner (in hundredths)																																																																																																						50.00%			50.00%
Preferred Equity Investment Additional funding, Maximum																																																																												14,000,000
Stated term of preferred equity investment (in years)																																																																											7 years																																				5 years			10 years
Preferred return on preferred equity investment (in hundredths)																																																																																																												10.10%			10.00%																																		9.50%
Preferred Returns Maturity Date																																																																																																																																																	May 31, 2016
Preferred return on preferred equity investment in first five years (in hundredths)																																																																																																																		9.00%
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)																																																																																																																9.00%	10.00%		13.00%																													9.50%
Net proceeds from sale of property																																																																																																																				1,600,000																		1,400,000
Balance sheets [Abstract]
Rental properties and real estate under development																																																																											1,659,078,000	1,745,147,000	1,659,078,000
Other assets																																																																											63,847,000	168,061,000	63,847,000
Total assets																																																																											1,722,925,000	1,913,208,000	1,722,925,000
Debt	(80,000,000)					(30,300,000)	(26,500,000)		(14,600,000)		(54,500,000)	(59,900,000)	(45,000,000)																																																														900,095,000	820,895,000	900,095,000			(17,500,000)	(450,000,000)
Other liabilities																																																																											48,518,000	91,922,000	48,518,000
Equity																																																																											774,312,000	1,000,391,000	774,312,000
Total liabilities and partners' equity																																																																											1,722,925,000	1,913,208,000	1,722,925,000
Company's share of equity																																																																											383,412,000	571,345,000	383,412,000
Statements of operations [Abstract]
Property revenues																																																																												130,128,000	106,386,000	54,699,000
Property operating expenses																																																																												(55,990,000)	(43,066,000)	(24,098,000)
Net operating income																																																																												74,138,000	63,320,000	30,601,000
Gain on sale of real estate																																																																												106,016,000	0	0
Interest expense																																																																												(34,959,000)	(27,843,000)	(13,619,000)
General and administrative																																																																												(3,697,000)	(1,748,000)	(709,000)
Depreciation and amortization																																																																												(47,917,000)	(44,412,000)	(20,850,000)
Net income (loss)																																																																												93,581,000	(10,683,000)	(4,577,000)
Company's share of net income (loss)																																																																												41,745,000	(467,000)	(1,715,000)
Projected debt service coverage ratio (in hundredths)																																																																																																												110.00%
Number of years the investment can not be repaid (in years)																																																																																																												2 years
Business Combination, Separately Recognized Transactions [Line Items]
Cost of acquired entity		103,300,000		551,100,000	103,300,000												17,000,000		31,400,000		27,000,000		13,800,000		14,100,000	23,000,000	16,000,000		23,700,000	48,300,000	52,000,000	31,600,000	34,000,000	15,900,000	148,000,000	96,000,000					429,200,000		92,000,000		151,300,000		132,900,000		27,800,000		25,200,000							45,600,000															73,800,000	22,200,000								660,500,000	38,300,000
Number of units acquired				2,052	386												73		121		63		63		66	60	100	349	90	276	248	126	92	90	508	147	2,495	449			2,013		373		882		438		160		160	230	314					264																								2,713	156	3,221
Mortgage loan on property acquired, interest rate (in hundredths)																														5.70%	5.60%		5.70%																																																		5.20%	3.83%
Mortgage loans on real estate interest rate term																														7 years	8 years		8 years																																																		8 years
Property acquired in month of December (in hundredths)																																																																									75.00%
Purchase Price		103,300,000		551,100,000	103,300,000												17,000,000		31,400,000		27,000,000		13,800,000		14,100,000	23,000,000	16,000,000		23,700,000	48,300,000	52,000,000	31,600,000	34,000,000	15,900,000	148,000,000	96,000,000					429,200,000		92,000,000		151,300,000		132,900,000		27,800,000		25,200,000							45,600,000															73,800,000	22,200,000								660,500,000	38,300,000
Units				2,052	386												73		121		63		63		66	60	100	349	90	276	248	126	92	90	508	147	2,495	449			2,013		373		882		438		160		160	230	314					264																								2,713	156	3,221
Quarter acquired																	Q1 2011		Q1 2011		Q2 2011		Q3 2011		Q4 2011																		Q2 2011		Q3 2011		Q3 2011		Q4 2011		Q4 2011									Q4 2012		Q4 2012		Q4 2012		Q4 2012		Q4 2012		Q4 2012		Q4 2012
Sales price of real estate				28,300,000	412,950,000																																																	17,200,000	11,100,000	16,000,000	7,400,000			42,200,000		31,000,000		56,300,000		50,100,000		33,100,000		26,500,000		173,750,000
Location																Los Angeles, CA		Santa Clara, CA		Los Angeles, CA		Seattle, WA		Redmond, WA																		Oxnard, CA		Redmond, WA		Woodland Hills, CA		Fremont, CA		Fremont, CA									Corona, CA		Oakland, CA		Studio City, CA		Seattle, WA		Chatsworth, CA		Snoqualmie, WA		San Jose, CA
Number of active development projects				9																																	7		2
Number of predevelopment projects Owned																																						2		1
Aggregate carrying value of Predevelopment charges																																						59,600,000
Estimated cost of active development projects																																					928,400,000
Estimated costs to be expended																																					463,900,000
Debt Instrument [Line Items]
Payment made for short term bridge loan to joint venture										26,000,000
Debt instrument, description of variable rate basis										LIBOR			LIBOR																																																																																																																												LIBOR
Debt instrument, basis spread on variable rate (in hundredths)				2.50%						2.50%					1.95%																																																																																																																										2.50%
Secured mortgage loans on real estate	80,000,000					30,300,000	26,500,000		14,600,000		54,500,000	59,900,000	45,000,000																																																														(900,095,000)	(820,895,000)	(900,095,000)			17,500,000	450,000,000
Premium for loan						4,300,000	4,100,000		2,400,000																																																																							2,300,000
Debt instrument, effective interest rate (in hundredths)						3.30%	3.10%		3.00%																																																																							3.10%
Debt instrument, number of extensions													2
Debt instrument, term of extensions (in years)														1 year
Estimated total cost of renovation	$ 4,000,000							$ 8,000,000
Mortgage loan on property acquired, maturity date											Oct. 31, 2046	Dec. 31, 2046
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%