Supplemental Disclosure of Non-Cash Investing and Financing Activities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of common stock as deferred compensation		$ 544
Issuance of units in the operating partnership	12,675	35,917
Redemption of units in the operating partnership	17,287	483
Derivative instruments at fair value	479	314
Mortgage assigned upon asset sale		59,099
Tenant improvements and capital expenditures payable	9,665	12,294
Assumption of mortgage loans	84,642
Fair value adjustment to noncontrolling interest in the Operating Partnership	36,091	46,810
Deferred leasing payable	4,872	2,583
Capital leased asset	9,992
Transfer to net assets held for sale	207,665	86,339
Transfer to liabilities related to net assets held for sale	11,894	62,792
Repayment of mezzanine loans		3,750
Redemption of Series E units		31,698
Repayment of financing receivable		28,195
Consolidation of real estate investments	$ 90,934

The increase during the period in capital lease assets due to entering into new capital leases.

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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- Definition

Represents the amount of deferred leasing payable.

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No definition available.

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- Definition

Represents fair value adjustments to derivative instruments.

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No definition available.

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- Definition

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

Represents reduction in financing receivables in noncash investing or financing transactions.

+ 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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- Definition

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

+ References

No definition available.

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- Definition

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

+ References

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- Definition

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

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65

-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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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

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-Paragraph A240

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- Definition

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

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-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

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-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

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-SubTopic 10

-Section 50

-Paragraph 5

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- Definition

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

+ References

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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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

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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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-Publisher AICPA

-Name Practice Bulletin (PB)

-Number 14

-Paragraph 15

-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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- Definition

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

-Article 5

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-Name Emerging Issues Task Force (EITF)

-Number 00-19

-Paragraph 12

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- Definition

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

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