Archstone Acquisition (Details) (USD $)	0 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended					0 Months Ended
	Feb. 27, 2013	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Archstone	Mar. 31, 2013 Archstone	Mar. 31, 2012 Archstone	Feb. 27, 2013 Archstone	Feb. 27, 2013 Archstone Archstone U.S. Fund	Feb. 27, 2013 Archstone Residual JV	Feb. 27, 2013 Archstone Apartment communities	Feb. 27, 2013 Archstone Equity
Archstone Acquisition
Percentage of assets and liabilities acquired							40.00%	28.60%	20.00%		60.00%
Land and land improvements							$ 1,760,100,000
Buildings and improvements							3,729,422,000
FF&E							52,290,000
Construction-in-progress, including land and land held for development							404,765,000
In-place lease intangibles							182,467,000
Other assets							85,829,000
Consolidated assets							6,214,873,000
Interest in unconsolidated real estate entities							256,454,000
Total assets							6,471,327,000
Fair value of assumed mortgage notes payable							3,732,980,000
Liability for preferred obligations							66,500,000
Other liabilities							34,100,000
Noncontrolling interest							13,262,000
Net Assets Acquired							2,624,485,000
Common shares issued							1,875,210,000
Cash consideration							749,275,000
Acquisition related expenses
Acquisition related expenses recognized		40,059,000	239,000		69,271,000
Acquisition related expenses reported as a component of equity in income (loss) of unconsolidated entities		(18,564,000)	2,175,000		29,457,000
Consideration
Number of shares issued	14,889,706	14,889,706
Value of shares issued							1,875,210,000
Cash payment							749,275,000
Fair value of indebtedness assumed							3,732,979,000
Principal amount of consolidated indebtedness		3,512,202,000		3,512,202,000	3,512,202,000		3,512,202,000
Debt fair value exceeds the principal face value		150,298,000					220,777,000
Redemption value of preferred equity				66,500,000	66,500,000		66,500,000
Debt repaid concurrent with acquisition							70,479,000
Information for acquisition that is included in condensed consolidated statement of operations comprehensive income from the acquisition date
Revenues		312,131,000	246,032,000	36,624,000
Loss attributable to common shareholders		75,427,000	57,758,000	(22,635,000)
Supplemental consolidated pro forma information
Revenues					384,078,000	344,479,000
Income from continuing operations					$ 106,853,000	$ 66,397,000
Earnings per common share - diluted (from continuing operations)					$ 0.84	$ 0.52
Lease-up period assumed to achieve stabilized occupancy										12 months