Organization and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) community building investment partnership apartment project shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) shares
Real Estate Properties [Line Items]
Ownership interest in partnership (as a percent)	96.70%
Apartment communities owned (in communities) | community	246
Apartment units owned (in units) | apartment	59,860
Ownership interest, number of commercial buildings (in commercial buildings) | building	1
Ownership interest, number of active development projects (in projects) | project	5
Sales and maturities of marketable securities	$ 24,900	$ 5,000
Available-for-sale securities, gross realized gain (loss)	$ 1,600	700
Downreit limited partnerships consolidated by company (in partnerships) | partnership	20
Communities within Downreit partnerships (in communities) | community	12
Number of previously consolidated co-investments considered VIE (in investments) | investment	9
Assets related to variable interest entities net of intercompany eliminations	$ 1,100,000		$ 989,300
Liabilities related to variable interest entities net of intercompany eliminations	351,100		288,100
Noncontrolling interest in variable interest entity	75,700		52,900
Fixed rate debt carrying amount	4,800,000
Fixed rate debt fair value	4,900,000
Investments in mortgage back securities, fair value	111,600		108,800
Capitalized internal costs related to development and redevelopment projects	$ 5,200	$ 4,500
Number of co-investments with financing distributions in excess of the company's investment (in investments) | investment	1
Mortgage Backed Securities [Member]
Real Estate Properties [Line Items]
Held-to-maturity securities, carrying value	$ 97,969		$ 94,393
Essex Portfolio, L.P. [Member]
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in units) | shares	2,251,920		2,237,290
Redemption value of operating partnership units outstanding	$ 521,400		$ 520,200