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Fair Value - Additional Information (Detail) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Fair Value of Financial Instruments [Line Items]
Debt Instrument Carrying Amount	$ 3,633,125,000	$ 4,068,417,000
Put Option
Fair Value of Financial Instruments [Line Items]
Noncontrolling interest acquired	9,070,000
Fair Value, Inputs, Level 3 \| Redeemable Noncontrolling Interests Temporary Equity \| Put Option
Fair Value of Financial Instruments [Line Items]
Redemption options (the Puts)	5,648,000	12,106,000
Fair Value, Inputs, Level 1 \| Redeemable Noncontrolling Interests Temporary Equity
Fair Value of Financial Instruments [Line Items]
Fair value of DownREIT units	980,000	1,721,000
Fair Value, Inputs, Level 2 \| Bond Indebtedness, Notes Payable and Outstanding Credit Facility
Fair Value of Financial Instruments [Line Items]
Debt Instrument Carrying Amount	3,633,125,000	4,068,417,000
Debt Instrument Fair Value	$ 3,838,360,000	$ 4,236,216,000

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents notes payable as of the balance sheet date.

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