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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 Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Fair value, as of the acquisition date, of potential payments under the contingent consideration arrangement including cash and shares.

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As of the reporting date, the carrying amount of noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. The noncontrolling interest holder's ownership (or holders' ownership) may be in the form of common shares (regardless of class), limited partnership units (regardless of class), non-preferential membership interests, or any other form of common equity regardless of investee entity legal form.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-SubTopic 10

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Fair Value of Derivatives and Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Available-for-sale equity securities		$ 3,900
Contingent purchase consideration	3,000
Unsecured debt instruments
Redeemable non-controlling interests in operating partnership	236,475	119,057	98,758
Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	89	4,380
Contingent purchase consideration		5,402
Unsecured debt instruments
Total liabilities	4,104,800	3,677,845
Redeemable non-controlling interests in operating partnership		119,057
Corporate Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Available-for-sale equity securities		3,866
Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	89	514
Derivatives - Interest rate contracts	13,660	6,597
Contingent purchase consideration	3,000
Mortgages [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	635,531	306,515
Secured debt instruments - variable rate
Secured debt instruments - variable rate	151,685	405,641
Tax exempt secured notes payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate		13,885
Secured debt instruments - variable rate
Secured debt instruments - variable rate	94,700	94,700
Fannie Mae credit facilities [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	799,584	927,413
Secured debt instruments - variable rate
Secured debt instruments - variable rate	310,451	260,450
Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	421,000	31,750
Unsecured Debt [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	1,675,189	1,625,492
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	0	3,866
Contingent purchase consideration		0
Unsecured debt instruments
Total liabilities	0	264,849
Redeemable non-controlling interests in operating partnership		0
Level 1 [Member] \| Corporate Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Available-for-sale equity securities		3,866
Level 1 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	0	0
Derivatives - Interest rate contracts	0	0
Contingent purchase consideration	0
Level 1 [Member] \| Mortgages [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 1 [Member] \| Tax exempt secured notes payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate		0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 1 [Member] \| Fannie Mae credit facilities [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 1 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	0	0
Level 1 [Member] \| Unsecured Debt [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	0	264,849
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	89	514
Contingent purchase consideration		0
Unsecured debt instruments
Total liabilities	13,660	6,597
Redeemable non-controlling interests in operating partnership		119,057
Level 2 [Member] \| Corporate Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Available-for-sale equity securities		0
Level 2 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	89	514
Derivatives - Interest rate contracts	13,660	6,597
Contingent purchase consideration	0
Level 2 [Member] \| Mortgages [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 2 [Member] \| Tax exempt secured notes payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate		0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 2 [Member] \| Fannie Mae credit facilities [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Level 2 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	0	0
Level 2 [Member] \| Unsecured Debt [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	0	0
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	0	0
Contingent purchase consideration		5,402
Unsecured debt instruments
Total liabilities	4,091,140	3,406,399
Redeemable non-controlling interests in operating partnership		0
Level 3 [Member] \| Corporate Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Available-for-sale equity securities		0
Level 3 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	0	0
Derivatives - Interest rate contracts	0	0
Contingent purchase consideration	3,000
Level 3 [Member] \| Mortgages [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	635,531	306,515
Secured debt instruments - variable rate
Secured debt instruments - variable rate	151,685	405,641
Level 3 [Member] \| Tax exempt secured notes payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate		13,885
Secured debt instruments - variable rate
Secured debt instruments - variable rate	94,700	94,700
Level 3 [Member] \| Fannie Mae credit facilities [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	799,584	927,413
Secured debt instruments - variable rate
Secured debt instruments - variable rate	310,451	260,450
Level 3 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	421,000	31,750
Level 3 [Member] \| Unsecured Debt [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments	$ 1,675,189	$ 1,360,643