Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 Entity Property
Portfolio Subject to Sale [Member]
Basis Of Presentation [Line Items]
Number of apartment properties owned by consolidated variable interest entities	18
Number of apartment properties owned by unconsolidated variable interest entities	130
Number of consolidated properties in portfolio	42
Number of unconsolidated properties in portfolio	130
Variable Interest Entity, Not Primarily Beneficiary Held Through Consolidated Tax Credit Funds in Which Company Holds Substantially All Economic Interests [Member]
Basis Of Presentation [Line Items]
Maximum risk or loss related to investment in ,receivable from, or contractual obligation to advance funds to unconsolidated VIEs	$ 5.2
Maximum risk of loss on investments in unconsolidated VIEs through consolidated VIEs in which we hold substantially all the economic interests	5.2
Receivables From Unconsolidated Variable Interest Entities [Member]
Basis Of Presentation [Line Items]
Maximum risk or loss related to investment in ,receivable from, or contractual obligation to advance funds to unconsolidated VIEs	96.9
Obligation to Advance Funds to Unconsolidated Variable Interest Entities [Member]
Basis Of Presentation [Line Items]
Maximum risk or loss related to investment in ,receivable from, or contractual obligation to advance funds to unconsolidated VIEs	3.0
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of units in apartment properties owned by consolidated variable interest entities	12,768
Carrying value of real estate collateralizing debt of consolidated VIEs	778.4
Carrying value of property debt of consolidated VIEs	632.6
Basis Of Presentation [Line Items]
Number of apartment properties owned by consolidated variable interest entities	81
Number of consolidated properties in portfolio	119
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of units in apartment properties owned by unconsolidated variable interest entities	12,331
Investments in unconsolidated VIEs through consolidated VIEs in which we hold an insignificant economic interest	$ 22.5
General partner or equivalent interest in consolidated tax credit funds that are VIEs and that own an interest in unconsolidated VIEs	1% or less
Basis Of Presentation [Line Items]
Number of apartment properties owned by unconsolidated variable interest entities	231
Number of unconsolidated properties in portfolio	178