Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) community building investment partnership apartment project shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) community building investment partnership apartment project shares	Sep. 30, 2018 USD ($)	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	249		249
Apartment units owned (in Shares) | apartment	60,620		60,620
Ownership interest, number of commercial buildings (in commercial buildings) | building	1		1
Ownership interest, number of active development projects (in projects) | project	7		7
Equity securities	$ 4,900		$ 4,900		$ 6,700
Sales and maturities of marketable securities	7,000	$ 3,500	57,200	$ 22,500
Marketable securities, realized gain (loss)	$ 200	100	700	700
Gain (loss) on sale of equity securities			$ 4,280	426
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	372,000		372,000		261,700
Noncontrolling interest in variable interest entity	129,900		129,900		64,500
Fixed rate debt carrying amount	5,200,000		5,200,000		5,000,000
Fixed rate debt fair value	5,500,000		5,500,000		5,000,000
Variable rate debt, carrying amount	839,200		839,200		619,600
Variable rate debt fair value	833,600		833,600		615,200
Investments in mortgage back securities, fair value	144,700		144,700		129,500
Capitalized internal costs related to development and redevelopment projects	4,300	4,700	13,100	14,200
Redeemable noncontrolling interest	39,077		39,077		35,475
Mortgage backed securities [Member]
Real Estate Properties [Line Items]
Investments in mortgage backed securities, carrying value	143,889		143,889		$ 127,187
Interest And Other Income [Member]
Real Estate Properties [Line Items]
Gain (loss) on sale of equity securities	$ (200)	$ 1,200	$ 4,300	400
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 Shares) | shares	2,298,237		2,298,237		2,305,389
Redemption value of operating partnership units outstanding	$ 750,700		$ 750,700		$ 565,300
Gain (loss) on sale of equity securities			4,280	$ 426
Redeemable noncontrolling interest	$ 39,077		$ 39,077		$ 35,475