Organization and Basis of Presentation - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) project community building partnership apartment shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) project community building partnership apartment shares	Sep. 30, 2015 USD ($)	Jan. 01, 2016 investment	Dec. 31, 2015 USD ($) shares
Real Estate Properties [Line Items]
Ownership interest in partnership (as a percent)			96.70%
Apartment communities owned (in communities) | community	244		244
Apartment units owned (in units) | apartment	59,290		59,290
Ownership interest, number of commercial buildings (in commercial buildings) | building	3		3
Ownership interest, number of active development projects (in projects) | project	6		6
Sales and maturities of marketable securities	$ 3,500,000	$ 0	$ 14,700,000	$ 2,000,000
Available-for-sale securities, gross realized gain (loss)	$ 1,000,000	0	2,900,000	0
Proceeds from sale of other investments		5,600,000	0	5,600,000
Gain (loss) on sale of other investments		600,000	$ 0	600,000
Number of previously consolidated co-investments considered VIE (in variable interest entities) | investment					9
Downreit limited partnerships consolidated by company (in number of partnerships) | partnership	19		19
Communities within Downreit partnerships (in communities) | community	11		11
Assets related to variable interest entities net of intercompany eliminations	$ 954,600,000		$ 954,600,000			$ 893,100,000
Liabilities related to variable interest entities net of intercompany eliminations	267,300,000		267,300,000			231,800,000
Noncontrolling interest in variable interest entity	52,300,000		52,300,000			54,600,000
Fixed rate debt carrying amount	5,000,000,000		5,000,000,000
Fixed rate debt fair value	5,300,000,000		5,300,000,000
Investments in mortgage back securities, fair value	105,900,000		105,900,000			110,200,000
Capitalized internal costs related to development and redevelopment projects	3,800,000	$ 2,900,000	10,600,000	$ 8,300,000
Mortgage Backed Securities [Member]
Real Estate Properties [Line Items]
Held-to-maturity securities, carrying value	$ 90,950,000		$ 90,950,000			$ 80,387,000
Essex Portfolio, L.P. [Member]
Real Estate Properties [Line Items]
Operating Partnership units outstanding (in units) | shares	2,219,268		2,219,268			2,214,545
Redemption value of operating partnership units outstanding	$ 494,200,000		$ 494,200,000			$ 530,200,000