Significant Transactions During the First Quarter of 2014 and Subsequent Events (Details) (USD $)	3 Months Ended			3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Common Stock [Member]	May 08, 2014 Subsequent Event [Member] Common Stock [Member]	Mar. 31, 2014 Secured Debt [Member]	Apr. 30, 2014 Unsecured Debt [Member] Subsequent Event [Member]	Mar. 31, 2014 Essex Apartment Value Fund II, LP [Member] Unit	May 31, 2014 Piedmont Apartments [Member] Subsequent Event [Member] Unit	Mar. 31, 2014 Avery [Member] Unit
Acquisitions [Abstract]
Cost of acquired entity									$ 76,800,000	$ 35,000,000
Number of units								1	396	121
Debt instrument assumed	1,408,232,000		1,404,080,000			44,800,000
Fixed rate of interest (in hundredths)						5.60%
Term of loan						3 years
Dispositions [Abstract]
Number of units disposed of								1	396	121
Remaining units communities owned								2
Proceed from sale of assets								23,800,000
Gain on sale of assets	8,268,000	1,503,000						11,400,000
Ownership percentage in Fund II (in hundredths)								28.20%
Income from Promotion								3,800,000
Common Stock [Abstract]
Equity distribution agreement (in shares)	0			958,000	197,600
Average share price (in dollars per share)				$ 166.24	$ 171.62
Proceed from stock issuance, net of fees and commissions	157,596,000	122,905,000		157,600,000	33,700,000
Unsecured Bond Offering [Abstract]
Debt instrument, principal amount							400,000,000
Stated interest rate (in hundredths)							3.875%
Net proceeds from issuance of debt							$ 394,000,000