Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($) apartment community project partnership building investment shares	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) apartment community project partnership building investment shares	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) partnership community investment shares
Real Estate Properties [Line Items]
Apartment communities owned (in communities) | community	246		246
Apartment units owned (in apartments) | apartment	60,920		60,920
Ownership interest, number of commercial buildings (in commercial buildings) | building	1		1
Ownership interest, number of active development projects (in projects) | project	2		2
Ownership interest, number of unconsolidated joint venture projects (in projects) | project	1		1
Equity securities	$ 2,500		$ 2,500		$ 2,500
Sales and maturities of marketable securities	100	$ 4,100	14,900	$ 4,300
Marketable securities, realized gain (loss)	$ (100)	46	2,500	33
Gain (loss) on sale of equity securities			$ 16,681	(1,073)
DownREIT limited partnerships consolidated by company (in partnerships) | partnership	18		18		17
Communities within DownREIT partnerships (in communities) | community	9		9		9
Number of previously consolidated co-investments considered VIE (in investments) | investment	6		6		5
Assets related to variable interest entities net of intercompany eliminations	$ 904,600		$ 904,600		$ 898,500
Liabilities related to variable interest entities net of intercompany eliminations	320,800		320,800		326,800
Noncontrolling interest in variable interest entity	122,500		122,500		120,800
Fixed rate debt carrying amount	5,700,000		5,700,000		5,500,000
Fixed rate debt fair value	6,100,000		6,100,000		6,000,000
Variable rate debt, carrying amount	408,900		408,900		775,100
Variable rate debt fair value	406,600		406,600		770,100
Capitalized internal costs related to development and redevelopment projects	5,500	8,900	11,900	18,800
Redeemable noncontrolling interest	35,026		35,026		$ 32,239
Interest And Other Income (Expense)
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	$ 10,400	$ 7,600	$ 16,700	(1,100)
Essex Portfolio, L.P.
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in shares) | shares	2,293,760		2,293,760		2,294,760
Redemption value of operating partnership units outstanding	$ 688,200		$ 688,200		$ 544,800
Gain (loss) on sale of equity securities			16,681	$ (1,073)
Redeemable noncontrolling interest	$ 35,026		$ 35,026		$ 32,239
Partnership Interest
Real Estate Properties [Line Items]
Ownership interest in partnership			96.60%		96.60%