Summary of Critical and Significant Accounting Policies - Summary of Merger (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended	9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014 property	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 01, 2014	Dec. 31, 2014
Business Acquisition [Line Items]
Cash consideration for BRE merger									$ 555,826,000	$ 0	$ 0
Business Acquisition, Pro Forma Information [Abstract]
Merger and integration expenses									53,530,000	4,284,000	0
Discontinued Operations, Number Of Properties Sold				3
Revenue, Net									969,305,000	609,266,000	535,153,000
Net income	44,805,000	58,582,000	4,645,000	26,406,000	36,903,000	75,875,000	29,575,000	29,702,000	134,438,000	172,055,000	139,590,000
BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Cash assumed	140,000								140,000				140,000
Rental properties and real estate under development	5,618,000								5,618,000				5,618,000
Real estate held for sale, net	108,000								108,000				108,000
Co-investments	218,000								218,000				218,000
Acquired in-place lease value	77,000								77,000				77,000
Other assets	16,000								16,000				16,000
Other liabilities	(1,747,000)								(1,747,000)				(1,747,000)
Redeemable noncontrolling interest	(94,000)								(94,000)				(94,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Redeemable Noncontrolling Interest	5,000								5,000				5,000
Total consideration for BRE merger	4,331,000								4,331,000			4,300,000,000	4,331,000
Increase in fair value of personal property													100,900,000
Cash consideration for BRE merger									556,000
Equity consideration for BRE merger	3,775,000								3,775,000				3,775,000
Number Of Property Units Contributed				14
Value Of Properties Contributed									1,400,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Acquired In-place Lease Value	19,000,000								19,000,000				19,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue									1,055,460,000	944,410,000
Business Acquisition, Pro Forma Net Income (Loss)									263,440,000	141,504,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted									$ 4.08	$ 2.26
Merger and integration expenses									53,500,000			4,300,000,000
Anti-dilutive securities (in shares)									23,100,000	23,100,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									105,000,000
Revenue, Net									283,300,000
Net income									17,200,000
Essex Portfolio, L.P. [Member]
Business Acquisition [Line Items]
Cash consideration for BRE merger									555,826,000	0	0
Business Acquisition, Pro Forma Information [Abstract]
Merger and integration expenses									53,530,000	4,284,000	0
Revenue, Net									969,305,000	609,266,000	535,153,000
Net income	44,805,000	58,582,000	4,645,000	26,406,000	36,903,000	75,875,000	29,575,000	29,702,000	134,438,000	172,055,000	139,590,000
Essex Portfolio, L.P. [Member] | BRE Properties, Inc. [Member]
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue									1,055,460,000	944,410,000
Business Acquisition, Pro Forma Net Income (Loss)									$ 263,585,000	$ 141,175,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted									$ 4.08	$ 2.26
Personal Property [Member] | BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Estimated useful life													5 years
Real Estate [Member] | BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Estimated useful life													30 years