Basis of Presentation and Summary of Significant Accounting Policies (Details Textuals) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Variable Interest Entity [Line Items]
Number of variable interest entities consolidated	125		125
Number of apartment properties owned by consolidated variable interest entities	84		84
Number of units in apartment properties owned by consolidated variable interest entities	12,982		12,982
Basis of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
General partner or equivalent interest in consolidated tax credit funds that are VIEs and that own an interest in unconsolidated VIEs	1% or less		1% or less
Maximum risk of loss on investments in unconsolidated VIEs through consolidated VIEs in which we hold substantially all the economic interests	$ 5,900,000		$ 5,900,000
Risk of loss related to carrying amount of receivables due from unconsolidated VIEs	99,800,000		99,800,000
Risk of loss related to contractual obligation to advance funds to unconsolidated VIEs	3,400,000		3,400,000
Notional amount of interest rate swaps	52,300,000		52,300,000		52,300,000
Interest rate swaps fair value	3,600,000		3,600,000		2,700,000
Weighted average term of interest rate swaps, in years	9.6		9.6
Consolidated Comprehensive loss	26,300,000	12,000,000	53,500,000	28,900,000
Estimated unrealized losses on interest rate swaps that will be reclassified into earnings during the next twelve months	1,600,000		1,600,000
Weighted average fixed rate related to the interest rate swaps	3.43%		3.43%
Borrowings subject to total rate of return swaps	164,300,000		164,300,000		276,900,000
Weighted average fixed receive rate under total rate of return swaps	6.40%		6.40%
Weighted average variable pay rate under total rate of return swaps	1.60%		1.60%
Carrying amount of real estate (held for use or held for sale) prior to recognition of impairment losses	56,500,000	35,900,000	56,500,000	35,900,000
Estimated aggregate fair value of notes receivable	114,700,000		114,700,000		116,000,000
Carrying amounts of notes receivable	127,300,000		127,300,000		127,600,000
Estimated aggregate fair value of consolidated debt (including amounts reported in liabilities related to assets held for sale)	5,500,000,000		5,500,000,000		5,600,000,000
Carrying amount of consolidated debt (including amounts reported in liabilities related to assets for sale)	5,400,000,000		5,400,000,000		5,500,000,000
Notional amount of total rate of return swaps	164,600,000		164,600,000
Carrying value of property debt of consolidated VIEs			643,500,000
Portion of par value notes estimated to be collectible	28,500,000		28,500,000
Portion of par value notes outstanding with stated maturity dates	18,900,000		18,900,000
Reduced amount of debt subject to total rate of return swaps			112,000,000
Amortized cost of the investment in securities	51,800,000		51,800,000
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of variable interest entities unconsolidated	244		244
Number of apartment properties owned by unconsolidated variable interest entities	297		297
Number of units in apartment properties owned by unconsolidated variable interest entities	18,606		18,606
Investments in unconsolidated VIEs through consolidated VIEs in which we hold an insignificant economic interest	42,800,000		42,800,000
Variable Interest Entity, Not Primary Beneficiary, Held Through Consolidated Tax Credit Funds in Which Company Holds Substantially All Economic Interests [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated VIEs held through consolidated tax credit funds that are VIEs and in which we hold substantially all the economic interests			5,900,000
Carrying Value [Member]
Basis Of Presentation [Line Items]
Carrying value of real estate collateralizing debt of consolidated VIEs			817,300,000
Unconsolidated Real Estate Partnerships [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum annual interest rates			4.30%
Maximum annual interest rates			12.00%
Average annual interest rates			9.80%
Non-Affiliates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum annual interest rates			2.10%
Maximum annual interest rates			8.80%
Average annual interest rates			4.10%
Notes receivable from non-affiliates	$ 99,900,000		$ 99,900,000		$ 103,900,000