Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) community building investment project apartment partnership shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) community investment partnership shares
Real Estate Properties [Line Items]
Apartment communities owned (in communities) | community	244
Apartment units owned (in apartments) | apartment	60,175
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	2
Equity securities	$ 2,400		$ 2,500
Sales and maturities of marketable securities	14,800	$ 200
Marketable securities, realized gain (loss)	2,600	(13)
Gain (loss) on sale of equity securities	$ 6,276	(8,696)
DownREIT limited partnerships consolidated by company (in partnerships) | partnership	18		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	$ 900,600		$ 898,500
Liabilities related to variable interest entities net of intercompany eliminations	323,700		326,800
Noncontrolling interest in variable interest entity	122,500		120,800
Fixed rate debt carrying amount	5,800,000		5,500,000
Fixed rate debt fair value	6,100,000		6,000,000
Variable rate debt, carrying amount	324,000		775,100
Variable rate debt fair value	322,200		770,100
Capitalized internal costs related to development and redevelopment projects	6,400	9,900
Redeemable noncontrolling interest	36,322		$ 32,239
Interest And Other Income
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	$ 6,300	(8,700)
Essex Portfolio, L.P.
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in shares) | shares	2,293,760		2,294,760
Redemption value of operating partnership units outstanding	$ 623,500		$ 544,800
Gain (loss) on sale of equity securities	6,276	$ (8,696)
Redeemable noncontrolling interest	$ 36,322		$ 32,239
Partnership Interest
Real Estate Properties [Line Items]
Ownership interest in partnership	96.60%		96.60%