Commitments and Contingencies (Details) (USD $)	12 Months Ended						1 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2012 person multiplier community home	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2007	Dec. 31, 2012 The Archstone Portfolio Acquisition	Nov. 30, 2012 Purchase Agreement Equity Residential	Nov. 30, 2012 Purchase Agreement The Archstone Portfolio Acquisition community home property	Nov. 30, 2012 Purchase Agreement Archstone Enterprise LP	Dec. 31, 2012 Maximum The Archstone Portfolio Acquisition	Dec. 31, 2012 Properties on land subject to land leases property item community	Dec. 31, 2012 Assets Held under Capital Leases community	Dec. 31, 2012 Restricted stock and stock options	Dec. 31, 2012 Restricted stock and stock options Minimum	Dec. 31, 2012 Restricted stock and stock options Maximum	Dec. 31, 2012 Officer Severance Program Vice presidents and senior vice presidents multiplier	Dec. 31, 2012 Officer Severance Program Executive vice presidents and CFO multiplier	Dec. 31, 2012 Officer Severance Program CEO multiplier	Dec. 31, 2012 Officer Severance Program Maximum
Acquisition
Percentage of assets and liabilities to be acquired						40.00%		40.00%
Number of apartment homes in communities acquired							22,222
Number of owned communities under construction	23						6
Estimated number of apartment homes in communities to be developed	9,602						1,666
Number of wholly owned parcels of land							3
Number of apartment homes on land							968
Ownership percentage in joint ventures not expected to be consolidated									40.00%
Cash paid							$ 669,000,000
Common stock to be issued (in shares)							14,889,706
Principal amount of indebtedness assumed							3,700,000,000
Redemption value of preferred equity							132,200,000
Number of apartment communities acquired							66
Termination fee if acquisition is not closed by March 26, 2013					800,000,000
Employment agreements and arrangements
Number of executive officers under agreement	3
Number of executives, case one	2
Compensation multiplier, case one	2
Compensation multiplier, if the termination is in connection with a sale of the company, case one	3
Number of executives, case two	1
Compensation multiplier, case two	1
Compensation multiplier, if the termination is in connection with a sale of the company, case two	2
Options exercise period upon termination without cause or retirement														12 months
Retirement age												50 years
Service period													10 years
Employee's age at retirement plus years of employment													70 years
Written notice period													6 months
Period of the non-compete agreement												1 year
Termination period following a sale event																		18 months
Compensation multiplier															1	2	3
Construction and development contingencies
Commitment to acquire parcels of land				111,000,000
Obligation under commitment satisfied by purchasing remaining parcels	27,709,000
Legal Contingencies
Settlement proceeds related to environmental contamination matters		1,303,000
Lease obligations
Number of apartment communities										11	1
Number of communities under construction										4
Number of commercial properties owned										2
Number of leased properties accounted for as operating leases										14
Number of leased properties with purchase options										4
Cost related to operating lease	17,604,000	16,887,000	35,356,000
Number of development rights owned	34										2
Capital lease obligation											$ 36,005,000