Real Estate Investments (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Gross carrying value of rental properties
Land	$ 698,982	$ 697,724
Building and improvements	3,722,243	3,693,579
Tenant improvements	463,816	442,808
Rental properties	$ 4,885,041	$ 4,834,111

Carrying amount as of the balance sheet date of long-lived, depreciable assets that include building structures held for productive use including any addition, improvement, or renovation to the structure, such as interior masonry, interior flooring, electrical, and plumbing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
-Paragraph 5

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Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of real estate held for productive use. This excludes land held for sale.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Carrying amount at the balance sheet date of long-lived, depreciable asset that is an addition or improvement to assets held under lease arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
-Paragraph 5

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Balance Type:	debit
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- Definition

Represents a total which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

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