Organization (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014 apartment building project community	Dec. 31, 2013	Dec. 31, 2012	Apr. 01, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General partner ownership interest (in hundredths)	96.70%	94.60%
Noncontrolling interest Operating Partnership	3.30%	5.40%
Operating Partnership units outstanding (in shares)	2,201,810	2,149,802
Redemption value of Operating Partnership units outstanding	$ 455,000,000	$ 309,000,000
Number of apartment communities owned	239
Apartment units owned	57,455
Ownership interests, number of commercial buildings	4
Ownership interests, number of active development projects	12
Business Acquisition [Line Items]
Merger and integration expenses	53,530,000	4,284,000	0
Share Price				$ 174
Share Price After Deducting Special Dividend And Cash Consideration				$ 164
BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Common shares conversion ratio in connection with merger				0.2971
Share price (in dollars per share)				$ 7.18
Merger and integration expenses	$ 53,500,000			$ 4,300,000,000
Special Dividend Declared Per Share				$ 5.15
Cash Consideration Per Share Before Special Dividend				$ 12.33
Stock Issued During Period, Shares, Acquisitions				23,100,000
Share Price				$ 61
Share Price After Deducting Special Dividend And Cash Consideration				$ 48.67