Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) partnership investment community shares	Sep. 30, 2020 shares	Sep. 30, 2020 community	Sep. 30, 2020 apartment	Sep. 30, 2020 building	Sep. 30, 2020 project	Sep. 30, 2020 partnership	Sep. 30, 2020 investment	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Real Estate Properties [Line Items]
Apartment communities owned (in communities)							247	1
Apartment units owned (in apartments) | apartment								60,387
Ownership interest, number of commercial buildings (in commercial buildings) | building									1
Ownership interest, number of active development projects (in projects) | project										3
Ownership interest, number of unconsolidated joint venture projects (in projects) | project										3
Accounting standards update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201712Member
Cumulative effect adjustment	$ 6,267,482	$ 6,415,004	$ 6,267,482	$ 6,415,004	$ 6,403,504								$ 6,352,881	$ 6,345,116	$ 6,393,844
Equity securities	2,700		2,700		$ 3,600
Sales and maturities of marketable securities	52,600	7,000	56,900	57,200
Marketable securities, realized gain	91	200	100	700
Gain (loss) on sale of equity securities			2,215	4,280
DownREIT limited partnerships consolidated by company (in partnerships) | partnership					17						17
Communities within DownREIT partnerships (in communities) | community					9		9
Number of previously consolidated co-investments considered VIE (in investments) | investment					6							5
Assets related to variable interest entities net of intercompany eliminations	900,000		900,000		$ 1,000,000
Liabilities related to variable interest entities net of intercompany eliminations	329,900		329,900		364,300
Noncontrolling interest in variable interest entity	121,200		121,200		122,500
Fixed rate debt carrying amount	5,800,000		5,800,000		5,200,000
Fixed rate debt fair value	6,000,000		6,000,000		5,400,000
Variable rate debt, carrying amount	804,900		804,900		660,400
Variable rate debt fair value	799,600		799,600		655,800
Investments in mortgage back securities, fair value	29,600		29,600		72,700
Capitalized internal costs related to development and redevelopment projects	6,100	11,000	24,900	32,100
Redeemable noncontrolling interest	30,719		30,719		37,410
Mortgage backed security
Real Estate Properties [Line Items]
Investments in mortgage backed securities, carrying value	29,578		29,578		$ 72,651
Interest And Other Income
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	3,300	(200)	2,200	$ 4,300
Essex Portfolio, L.P.
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in shares) | shares					2,301,653	2,295,510
Redemption value of operating partnership units outstanding	460,900		$ 460,900		$ 692,500
Accounting standards update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201712Member
Gain (loss) on sale of equity securities			$ 2,215	$ 4,280
Redeemable noncontrolling interest	30,719		$ 30,719		$ 37,410
Partnership Interest
Real Estate Properties [Line Items]
Ownership interest in partnership			96.60%		96.60%
Distributions in Excess of Accumulated Earnings
Real Estate Properties [Line Items]
Cumulative effect adjustment	$ (821,841)	$ (887,521)	$ (821,841)	$ (887,521)	$ (887,619)								$ (760,028)	$ (857,994)	$ (812,796)
Cumulative Effect, Period Of Adoption, Adjusted Balance | Distributions in Excess of Accumulated Earnings
Real Estate Properties [Line Items]
Cumulative effect adjustment					$ 200