Real Estate Schedule of Real Estate Properties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Real Estate [Abstract]
Land	$ 2,605,162	$ 2,356,522
Land held for future development	275,094	266,822
Buildings and improvements	9,517,343	8,658,468
Tenant improvements	1,435,508	1,262,616
Furniture, fixtures and equipment	23,441	26,359
Construction in progress	1,036,780	818,685
Total	14,893,328	13,389,472
Less: accumulated depreciation	(2,934,160)	(2,642,986)
Total real estate	$ 11,959,168	$ 10,746,486

Gross amount, at the balance sheet date, of long-lived assets under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service.

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 5

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-SubTopic 10

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Gross amount, at the balance sheet date, of long-lived, depreciable assets commonly used in offices and stores. Examples include desks, chairs, and store fixtures.

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Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements.

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

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-Name Accounting Standards Codification

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

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Carrying amount of land available for development.

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

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The cumulative amount of depreciation for real estate property held for investment purposes.

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Amount of real estate investment property 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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Amount of real estate investment property, net of accumulated depreciation, 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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