Organization and Basis of Presentation - Narrative (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) community building partnership apartment project shares	Mar. 31, 2015 USD ($)	Jan. 01, 2016 investment	Dec. 31, 2015 USD ($) shares
Real Estate Properties [Line Items]
Ownership interest in partnership	96.70%
Apartment communities owned | community	244
Apartment units owned | apartment	59,441
Ownership interest, number of commercial buildings | building	2
Ownership interest, number of active development projects | project	7
Sales and maturities of marketable securities	$ 5,000,000	$ 700,000
Available-for-sale securities, gross realized gain (loss)	$ 700,000	0
Number of previously consolidated co-investments considered VIE | investment			9
Downreit limited partnerships consolidated by company | partnership	19
Communities within Downreit partnerships | community	11
Assets related to variable interest entities net of intercompany eliminations	$ 904,400,000			$ 893,100,000
Liabilities related to variable interest entities net of intercompany eliminations	231,400,000			231,800,000
Noncontrolling interest in variable interest entity	55,000,000			54,600,000
Fixed rate debt carrying amount	4,600,000,000
Fixed rate debt fair value	4,800,000,000
Investments in mortgage back securities, fair value	113,300,000			110,200,000
Capitalized internal costs related to development and redevelopment projects	3,200,000	$ 2,000,000
Collateralized Mortgage Backed Securities [Member]
Real Estate Properties [Line Items]
Held-to-maturity securities, carrying value	$ 83,932,000			$ 80,387,000
Essex Portfolio, L.P. [Member]
Real Estate Properties [Line Items]
Operating Partnership units outstanding | shares	2,224,968			2,214,545
Redemption value of operating partnership units outstanding	$ 520,300,000			$ 530,200,000