Supplemental Disclosure of Non-Cash Investing and Financing Activities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of common stock as deferred compensation	$ 631	$ 621
Issuance of units in the operating partnership	40,542	20,222
Redemption of units in the operating partnership	17,467	865
Derivative instruments at fair value	375	1,674
Assignment of debt investment to joint venture	25,362	286,571
Mortgage assigned upon asset sale	59,099	30,000
Tenant improvements and capital expenditures payable	10,056	8,686
Assumption of mortgage loans		663,767
Fair value adjustment to noncontrolling interest in operating partnership	44,893	1,168
Accrued acquisition liabilities	4,372	43,000
Issuance of common stock in connection with an acquisition		14,997
Consolidation of real estate investments		557,314
Transfer to net assets held for sale	86,339
Transfer to liabilities related to net assets held for sale	62,792
Repayment of mezzanine loan	3,750
Redemption of Series E units	31,698
Repayment of financing receivables	28,195
Investment in joint venture	$ 5,135

Future cash outflow to pay for liabilities incurred by the acquirer in a business acquisition.

No definition available.

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- Definition

Represents the change in the carrying value of real estate investments resulting from consolidation.

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No definition available.

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Represents fair value adjustments to derivative instruments.

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No definition available.

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- Definition

The investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group in noncash investing or financing transactions.

+ References

No definition available.

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Represents the fair value adjustment to the noncontrolling interest in the operating partnership.

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No definition available.

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- Definition

The cash outflow from the repayment of financing receivables in noncash transactions during the reporting period.

+ References

No definition available.

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- Definition

Value of liabilities transferred to liabilities related to assets held-for-sale in noncash transactions during the reporting period.

+ References

No definition available.

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Value of assets transferred to assets held-for-sale in noncash transactions during the reporting period.

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No definition available.

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- Definition

Future cash outflow to pay for purchases of fixed assets that have occurred.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

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-Topic 230

-SubTopic 10

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- Definition

The total fair value of shares issued during the period under a deferred compensation arrangement.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

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-Subparagraph b

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- Definition

The fair value of loans assumed in noncash investing or financing activities.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

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-Paragraph 5

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

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- Definition

The value of notes retired (or transferred to another entity) in noncash investing or financing transactions.

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- Definition

Total change in each class of partners' capital accounts during the year due to redemptions and adjustments to redemption value. All partners include general, limited and preferred partners.

+ References

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

-Publisher AICPA

-Name Practice Bulletin (PB)

-Number 14

-Paragraph 15

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

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-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 87-21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Total change in each class of partners' capital accounts during the year due to the sale of units. All partners include general, limited and preferred partners.

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The fair value of stock issued in noncash financing activities.

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The aggregate amount to be paid by the entity upon redemption of the security that is classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.27(b))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 28

-Subparagraph b

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-Name Emerging Issues Task Force (EITF)

-Number 00-19

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The fair value of transfer of mortgage payable in noncash investing or financing activities.

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Value of investments transferred from the entity's investments in noncash transactions.

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