Real Estate Schedule of Real Estate Properties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Real Estate [Abstract]
Land	$ 4,450,532	$ 2,605,162
Land held for future development	297,376	275,094
Buildings and improvements	11,065,113	9,517,343
Tenant improvements	1,617,401	1,435,508
Furniture, fixtures and equipment	25,164	23,441
Construction in progress	1,523,179	1,036,780
Total	18,978,765	14,893,328
Less: accumulated depreciation	(3,161,571)	(2,934,160)
Total real estate	$ 15,817,194	$ 11,959,168

Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.

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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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Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

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Carrying amount of land available for development.

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Amount before accumulated depreciation of additions or improvements to assets held under a 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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