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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fixed interest rate related to the interest rate derivative.

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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unsecured Debt - Narrative (Details)	1 Months Ended					3 Months Ended	12 Months Ended
Unsecured Debt - Narrative (Details)	Jun. 30, 2020 USD ($)	Apr. 30, 2020 USD ($) extension	Jan. 31, 2020	Nov. 30, 2016 USD ($)	Apr. 30, 2013 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) extension instrument line_of_credit	Dec. 31, 2019 USD ($)	Aug. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Oct. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Mar. 31, 2018 USD ($)	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)	Apr. 30, 2016	Mar. 31, 2015 USD ($)	Apr. 30, 2014 USD ($)
Debt Instrument [Line Items]
Senior notes							$ 200,000,000	$ 200,000,000.0
Effective interest rate							4.40%	4.40%
Unsecured debt, net							$ 5,607,985,000	$ 4,763,206,000
Debt instrument face amount							$ 4,900,000,000	4,250,000,000
Number of lines of credit \| line_of_credit							2
Lines of credit							$ 0	55,000,000
CPPIB Interest
Debt Instrument [Line Items]
Investment interest acquired			45.00%
Essex Portfolio, L.P.
Debt Instrument [Line Items]
Unsecured debt, net							5,607,985,000	4,763,206,000
Lines of credit							0	55,000,000
Unsecured Bonds 2.650%
Debt Instrument [Line Items]
Debt instrument face amount							650,000,000	0
Unsecured Bonds 1.650%
Debt Instrument [Line Items]
Debt instrument face amount							300,000,000	0
Unsecured Bonds 2.650%
Debt Instrument [Line Items]
Debt instrument face amount							300,000,000	0
Unsecured Bonds 3.000%
Debt Instrument [Line Items]
Debt instrument face amount							550,000,000	550,000,000
Unsecured Bonds 4.000%
Debt Instrument [Line Items]
Debt instrument face amount							500,000,000	500,000,000
Unsecured Bonds 4.500%
Debt Instrument [Line Items]
Debt instrument face amount							300,000,000	300,000,000
Unsecured Bonds 3.625%
Debt Instrument [Line Items]
Debt instrument face amount							350,000,000	350,000,000
Unsecured Bonds 3.375%, Due April 2026
Debt Instrument [Line Items]
Debt instrument face amount							450,000,000.0	450,000,000
Unsecured Bonds 5.200%
Debt Instrument [Line Items]
Debt instrument face amount							0	300,000,000
Unsecured Bonds 3.375%
Debt Instrument [Line Items]
Debt instrument face amount							300,000,000	300,000,000
Unsecured Bonds 3.875%
Debt Instrument [Line Items]
Debt instrument face amount							400,000,000	400,000,000
Unsecured Bonds 3.250%
Debt Instrument [Line Items]
Debt instrument face amount							300,000,000	300,000,000
Unsecured Bonds 3.625%
Debt Instrument [Line Items]
Debt instrument face amount							0	300,000,000
Variable Rate Term Loan
Debt Instrument [Line Items]
Unsecured debt, net				$ 350,000,000.0			$ 550,000,000.0	$ 350,000,000.0										$ 225,000,000.0
Weighted average interest rate							1.70%	2.70%
Basis spread on rate				0.95%
Variable Rate Term Loan \| February 2022
Debt Instrument [Line Items]
Unsecured debt, net							$ 350,000,000.0
Variable Rate Term Loan \| April 2021
Debt Instrument [Line Items]
Unsecured debt, net							$ 200,000,000.0
Number of extension options \| extension							2
Term extension period							12 years
Variable Rate Term Loan \| Carrying Value
Debt Instrument [Line Items]
Unsecured debt, net							$ 549,380,000	$ 349,189,000
Senior Notes \| Essex Portfolio, L.P.
Debt Instrument [Line Items]
Debt instrument face amount									$ 600,000,000.0
Senior Notes \| BRE Properties, Inc.
Debt Instrument [Line Items]
Unsecured debt, net							296,800,000	599,400,000
Long-term debt acquired																					$ 900,000,000.0
Senior Notes \| Unsecured Bonds 2.650%
Debt Instrument [Line Items]
Unsecured debt, net							$ 650,700,000
Debt instrument face amount	$ 150,000,000.0
Coupon rate							2.65%
Debt offering price	105.66%
Reoffer yield percentage	2.093%
Senior Notes \| Unsecured Bonds 2.650% \| Essex Portfolio, L.P.
Debt Instrument [Line Items]
Debt instrument face amount										$ 500,000,000.0
Coupon rate										2.65%
Debt offering price										99.628%
Repayments of secured debt						$ 100,300,000
Senior Notes \| Unsecured Bonds 1.650%
Debt Instrument [Line Items]
Coupon rate							1.65%
Debt offering price									99.035%
Senior Notes \| Unsecured Bonds 1.650% \| Essex Portfolio, L.P.
Debt Instrument [Line Items]
Unsecured debt, net							$ 294,500,000
Debt instrument face amount									$ 300,000,000.0
Coupon rate									1.65%
Senior Notes \| Unsecured Bonds 2.650%
Debt Instrument [Line Items]
Coupon rate							2.65%
Debt offering price									99.691%
Senior Notes \| Unsecured Bonds 2.650% \| Essex Portfolio, L.P.
Debt Instrument [Line Items]
Unsecured debt, net							$ 295,700,000
Debt instrument face amount									$ 300,000,000.0
Coupon rate									2.65%
Senior Notes \| Unsecured Bonds 3.000%
Debt Instrument [Line Items]
Unsecured debt, net							$ 543,100,000	542,300,000
Debt instrument face amount											$ 150,000,000.0	$ 400,000,000.0
Coupon rate							3.00%					3.00%
Debt offering price											101.685%	98.632%
Senior Notes \| Unsecured Bonds 4.000%
Debt Instrument [Line Items]
Unsecured debt, net							$ 494,800,000	494,100,000
Debt instrument face amount													$ 150,000,000.0	$ 350,000,000.0
Coupon rate							4.00%							4.00%
Debt offering price													100.717%	99.188%
Senior Notes \| Unsecured Bonds 4.500%
Debt Instrument [Line Items]
Unsecured debt, net							$ 295,800,000	295,600,000
Debt instrument face amount															$ 300,000,000.0
Coupon rate							4.50%								4.50%
Debt offering price															99.591%
Senior Notes \| Unsecured Bonds 3.625%
Debt Instrument [Line Items]
Unsecured debt, net							$ 346,800,000	346,300,000
Debt instrument face amount																$ 350,000,000.0
Coupon rate							3.625%
Debt offering price																99.423%
Senior Notes \| Unsecured Bonds 3.375%, Due April 2026
Debt Instrument [Line Items]
Unsecured debt, net							$ 446,400,000	445,700,000
Coupon rate							3.375%
Debt offering price																			99.386%
Senior Notes \| Unsecured Bonds 5.500%
Debt Instrument [Line Items]
Coupon rate																					5.50%
Face amount of debt paid off																	$ 300,000,000.0
Senior Notes \| Unsecured Bonds 5.200%
Debt Instrument [Line Items]
Coupon rate							5.20%
Face amount of debt paid off							$ 300,000,000.0
Senior Notes \| Unsecured Bonds 3.375%
Debt Instrument [Line Items]
Coupon rate							3.375%
Senior Notes \| Unsecured Bonds 3.875%
Debt Instrument [Line Items]
Unsecured debt, net							$ 397,800,000	397,100,000
Debt instrument face amount																					$ 400,000,000.0
Coupon rate							3.875%														3.875%
Debt offering price																					99.234%
Senior Notes \| Unsecured Bonds 3.250%
Debt Instrument [Line Items]
Coupon rate					3.25%		3.25%
Debt offering price					99.152%
Proceeds from issuance of unsecured debt					$ 300,000,000.0
Long-term debt, gross							$ 298,700,000	298,200,000
Senior Notes \| Unsecured Bonds 3.625%
Debt Instrument [Line Items]
Debt instrument face amount									$ 300,000,000.0
Coupon rate							3.625%		3.625%
Term Loan
Debt Instrument [Line Items]
Number of extension options \| extension		2
Term extension period		12 months
Debt instrument face amount		$ 200,000,000.0
Term Loan \| LIBOR
Debt Instrument [Line Items]
Basis spread on rate		1.20%
Unsecured Debt \| Senior Unsecured Notes Maturing April 1, 2025
Debt Instrument [Line Items]
Senior notes							$ 497,600,000	$ 497,100,000
Debt instrument face amount																				$ 500,000,000.0
Coupon rate																				3.50%
Debt offering price																				99.747%
Unsecured Line of Credit
Debt Instrument [Line Items]
Weighted average interest rate							1.00%	2.50%
Lines of credit							$ 0	$ 55,000,000
Unsecured Line of Credit \| Line of Credit Working Capital
Debt Instrument [Line Items]
Lines of credit							0	0
Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity							1,240,000,000
Line of Credit \| Line of Credit Working Capital
Debt Instrument [Line Items]
Maximum borrowing capacity							35,000,000.0
Line of Credit \| Unsecured Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity							1,200,000,000
Lines of credit							$ 0	$ 55,000,000.0
Line of Credit \| Unsecured Line of Credit \| LIBOR
Debt Instrument [Line Items]
Basis spread on rate							0.825%
Line of Credit \| Working Capital Unsecured Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 35,000,000.0
Interest Rate Swap \| Variable Rate Term Loan
Debt Instrument [Line Items]
Number of derivative instruments held \| instrument							5
Term of loan							5 years
Interest Rate Swap \| Variable Rate Term Loan \| Variable Term Loan, Tranche One
Debt Instrument [Line Items]
Derivative notional amount							$ 175,000,000.0
Derivative, fixed interest rate							2.30%