Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) community building investment partnership apartment project shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) community building investment partnership apartment project shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) community investment partnership shares	Jan. 01, 2019 USD ($)
Real Estate Properties [Line Items]
Ownership interest in partnership			96.60%		96.60%
Apartment communities owned (in communities) | community	246		246
Apartment units owned (in units) | apartment	59,962		59,962
Ownership interest, number of commercial buildings (in commercial buildings) | building	1		1
Ownership interest, number of active development projects (in projects) | project	6		6
Equity securities	$ 6,800		$ 6,800		$ 6,700
Sales and maturities of marketable securities	33,400	$ 9,400	50,200	$ 19,000
Marketable securities, realized gain (loss)	$ 600	(200)	$ 500	500
Downreit limited partnerships consolidated by company (in partnerships) | partnership	17		17		16
Communities within Downreit partnerships (in communities) | community	9		9		8
Number of previously consolidated co-investments considered VIE (in investments) | investment	7		7		8
Assets related to variable interest entities net of intercompany eliminations	$ 1,000,000		$ 1,000,000		$ 849,800
Liabilities related to variable interest entities net of intercompany eliminations	369,100		369,100		261,700
Noncontrolling interest in variable interest entity	129,300		129,300		64,500
Fixed rate debt carrying amount	5,100,000		5,100,000		5,000,000
Fixed rate debt fair value	5,300,000		5,300,000		5,000,000
Variable rate debt, carrying amount	736,300		736,300		619,600
Variable rate debt fair value	731,300		731,300		615,200
Investments in mortgage back securities, fair value	140,100		140,100		129,500
Capitalized internal costs related to development and redevelopment projects	4,000	4,500	8,800	9,500
Redeemable noncontrolling interest	36,830		36,830		35,475
Mortgage backed securities [Member]
Real Estate Properties [Line Items]
Investments in mortgage backed securities, carrying value	138,089		138,089		$ 127,187
Interest And Other Income [Member]
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	$ 56	$ 100	$ 4,500	$ (800)
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	2,299,237		2,299,237		2,305,389
Redemption value of operating partnership units outstanding	$ 671,200		$ 671,200		$ 565,300
Redeemable noncontrolling interest	$ 36,830		$ 36,830		$ 35,475