Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) community building investment partnership apartment project shares	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) shares
Real Estate Properties [Line Items]
Ownership interest in partnership	96.60%		96.60%
Apartment communities owned (in communities) | community	245
Apartment units owned (in units) | apartment	59,662
Ownership interest, number of commercial buildings (in commercial buildings) | building	1
Ownership interest, number of active development projects (in projects) | project	6
Equity securities	$ 6,800		$ 6,700
Sales and maturities of marketable securities	16,800	$ 9,600
Marketable securities, realized gain (loss)	$ (100)	700
Downreit limited partnerships consolidated by company (in partnerships) | partnership	16
Communities within Downreit partnerships (in communities) | community	8
Number of previously consolidated co-investments considered VIE (in investments) | investment	8
Assets related to variable interest entities net of intercompany eliminations	$ 876,200		849,800
Liabilities related to variable interest entities net of intercompany eliminations	268,500		261,700
Noncontrolling interest in variable interest entity	64,100		64,500
Fixed rate debt carrying amount	5,100,000		5,000,000
Fixed rate debt fair value	5,200,000		5,000,000
Variable rate debt, carrying amount	619,500		619,600
Variable rate debt fair value	615,000		615,200
Investments in mortgage back securities, fair value	135,600		129,500
Capitalized internal costs related to development and redevelopment projects	4,800	$ 5,000
Redeemable noncontrolling interest	37,169		35,475
Mortgage backed securities [Member]
Real Estate Properties [Line Items]
Investments in mortgage backed securities, carrying value	132,525		$ 127,187
Interest And Other Income [Member]
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	4,500
ASU 2017-12 [Member]
Real Estate Properties [Line Items]
Accumulated other comprehensive loss, cumulative effect adjustment, accumulated net hedge ineffectiveness	$ 200
Essex Portfolio, L.P. [Member]
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in units) | shares	2,299,379		2,305,389
Redemption value of operating partnership units outstanding	$ 665,100		$ 565,300
Redeemable noncontrolling interest	$ 37,169		$ 35,475