Real Estate Investments - Co-Investments (Details) $ in Thousands	1 Months Ended						3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) community unit	Nov. 30, 2017 USD ($) apartment	Oct. 31, 2017 USD ($)	Aug. 31, 2017 USD ($) apartment	Mar. 31, 2017 USD ($) unit	Jan. 31, 2017 USD ($) community unit	Mar. 31, 2017 USD ($) unit	Dec. 31, 2017 USD ($) community unit	Dec. 31, 2016 USD ($) community unit	Dec. 31, 2015 USD ($) community unit	Dec. 31, 2010
Business Acquisition [Line Items]
Ownership Percentage											3.00%
Number of apartment communities owned | community	247							247
Gain on remeasurement of co-investment								$ 88,641	$ 0	$ 34,014
Purchase Price								$ 273,000
Number of units sold | unit								270	323	848
Sales Price								$ 132,500	$ 80,800	$ 308,800
Gain on sale of properties								26,200	14,000	44,900
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	$ 1,119,258							$ 1,119,258	1,161,275
Number of units acquired | unit								1,328
Acquisitions of real estate and acquisition related capital expenditures								$ 206,194	$ 315,632	$ 515,726
Number of communities sold | community								1	3	2
Gain on sale of real estate and land								$ 26,423	$ 154,561	$ 47,333
Rental properties and real estate under development	355,735							355,735	190,505
Other liabilities	33,132							33,132	32,922
Gain on sale of real estate								26,200
Interest expense								(222,894)	(219,654)	(204,827)
General and administrative								(41,385)	(40,751)	(40,090)
Equity income from co-investments								86,445	48,698	21,861
Investments With Related Parties [Member]
Business Acquisition [Line Items]
Equity income from co-investments								1,900	3,400	3,700
Secured Note Receivable, 3.5% Interest Rate, Due December 16, 2017 [Member] | Affiliated Entity [Member] | Wesco V Property [Member]
Business Acquisition [Line Items]
Notes receivable, related parties				$ 55,000
Notes receivable, related party, interest rate				3.50%
BEXAWE, LLC [Member]
Business Acquisition [Line Items]
Repayments of debt	$ 66,200
Number of communities sold | community	2
Proceeds from sale of real estate	$ 160,300
Gain on sale of real estate and land	34,800
Membership Interest In Sage At Cupertino [Member]
Business Acquisition [Line Items]
Encumberance of mortgage debt					$ 52,000		$ 52,000
Number of units in real estate property | unit					230		230
Essex Ownership Percentage					40.50%		40.50%
Purchase Price					$ 90,000		$ 90,000
Number of units acquired | unit					230		230
Madrid In Mission Viejo [Member] | Wesco I [Member]
Business Acquisition [Line Items]
Number of units sold | apartment				230
Sales Price				$ 83,000
Gain on sale of properties				10,100
Repayments of debt				$ 30,100
Wesco V Property [Member]
Business Acquisition [Line Items]
Ownership Percentage				50.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures				$ 150,000
Eighth And Republican Avenue Property [Member]
Business Acquisition [Line Items]
Number of units acquired | apartment				211
Acquisitions of real estate and acquisition related capital expenditures				$ 101,300
Wesco V, San Jose Apartment Community [Member] | Wesco V Property [Member]
Business Acquisition [Line Items]
Number of units acquired | apartment				213
Asset acquisition, consideration transferred				$ 133,500
Asset acquisition, liabilities assumed				$ 57,900
Asset acquisition, liabilities assumed, effective interest rate				3.40%
Wesco I [Member]
Business Acquisition [Line Items]
Ownership Percentage			58.00%
Promote interest earned			$ 38,000
Village At Toluca Lake [Member] | Affiliated Entity [Member]
Business Acquisition [Line Items]
Notes receivable, related parties		$ 29,500
Notes receivable, related party, interest rate		3.50%
Village At Toluca Lake [Member] | BEX III [Member]
Business Acquisition [Line Items]
Number of units acquired | apartment		145
Acquisitions of real estate and acquisition related capital expenditures		$ 59,000
Total operating co investments [Member]
Business Acquisition [Line Items]
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	$ 780,332							$ 780,332	$ 781,905
Number of apartments owned through joint ventures | unit	10,810							10,810	11,274
CPPIB [Member]
Business Acquisition [Line Items]
Ownership Percentage								54.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	$ 500,287							$ 500,287	$ 422,068
Wesco I, III, and IV [Member]
Business Acquisition [Line Items]
Ownership Percentage								53.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	214,408							$ 214,408	180,687
Palm Valley [Member]
Business Acquisition [Line Items]
Ownership Percentage						50.00%		50.00%
Encumberance of mortgage debt									220,000
Number of units in real estate property | unit						1,098
Number of apartment communities owned | community						4
Gain on remeasurement of co-investment						$ 88,600
Essex Ownership Percentage					100.00%		100.00%
Purchase Price						$ 183,000	$ 183,000
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	0							$ 0	68,396
Number of units acquired | unit							1,098
BEXAEW, BEXII and BEX III [Member]
Business Acquisition [Line Items]
Ownership Percentage								50.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	13,827							$ 13,827	67,041
BEX II [Member]
Business Acquisition [Line Items]
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	(36,700)							$ (36,700)
BEX III [Member]
Business Acquisition [Line Items]
Ownership Percentage		50.00%
Other [Member]
Business Acquisition [Line Items]
Ownership Percentage								52.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	51,810							$ 51,810	43,713
Total development co investments [Member]
Business Acquisition [Line Items]
Ownership Percentage								50.00%
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	$ 73,770							$ 73,770	$ 157,317
Number of apartments owned through joint ventures | unit	814							814	1,427
Total preferred interest investments [Member]
Business Acquisition [Line Items]
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	$ 265,156							$ 265,156	$ 222,053
Total preferred interest investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Business Acquisition [Line Items]
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures	15,700							15,700	35,800
Total co investment [Member]
Business Acquisition [Line Items]
Rental properties and real estate under development	3,722,778							3,722,778	3,807,245
Other assets	110,333							110,333	121,505
Total assets	3,833,111							3,833,111	3,928,750
Debt	1,705,051							1,705,051	1,617,639
Other liabilities	45,515							45,515	74,607
Equity	2,082,545							2,082,545	2,236,504
Total liabilities and equity	3,833,111							3,833,111	3,928,750
Company's share of equity	$ 1,155,984							1,155,984	1,161,275
Property revenues								312,841	289,011	260,175
Property operating expenses								(110,583)	(99,637)	(93,067)
Net operating income								202,258	189,374	167,108
Gain on sale of real estate								90,663	28,291	14
Interest expense								(62,844)	(46,894)	(44,834)
General and administrative								(9,091)	(7,448)	(5,879)
Depreciation and amortization								(118,048)	(103,986)	(103,613)
Net income								102,938	59,337	12,796
Company's share of net income								$ 86,445	$ 48,698	$ 21,861