Investments in real estate (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Investments in real estate
Land (related to rental properties)	$ 472,977	$ 456,940
Buildings and building improvements	4,139,115	3,906,689
Other improvements	184,600	183,140
Rental properties	4,796,692	4,546,769
Less: accumulated depreciation	(679,081)	(616,007)
Rental properties, net	4,117,611	3,930,762
Construction in progress (CIP)/current value-added projects:
Active redevelopment	296,225	248,651
Active development	238,433	134,758
Projects in India and China	107,934	98,327
Construction in progress (CIP)/current value-added projects	642,592	481,736
Land/future value-added projects:
Land held for future development	534,618	431,838
Land undergoing preconstruction activities (additional CIP)	521,753	563,800
Land/future value-added projects	1,056,371	995,638
Investment in unconsolidated real estate entity	38,778	36,678
Investments in real estate, net	$ 5,855,352	$ 5,444,814

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Costs of real estate projects undergoing active development.

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Costs of real estate projects undergoing active redevelopment.

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Costs of CIP/current value-added redevelopment and development projects.

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Costs of projects primarily focused for our current client tenants and other life science relationship entities in India and China.

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Carrying amount as of the balance sheet date of improvements not otherwise specified in the existing taxonomy.

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Represents the aggregate carrying amount of land held for future development and land undergoing preconstruction activities expressed as land/future value-added projects.

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Represents the carrying amount of land undergoing preconstruction activities (consisting of Building Information Modeling (3-D virtual modeling), design development and construction drawings, sustainability and energy optimization review, budgeting, planning for future site and infrastructure work, and other activities prior to commencement of vertical construction of aboveground shell and core improvements) that are also classified as construction in progress. Our objective with preconstruction is to reduce the time it takes to deliver projects to prospective tenants. Project costs are capitalized as a cost of the project during periods when activities necessary to prepare an asset for its intended use are in progress. If vertical aboveground construction is not initiated at completion of preconstruction activities, the land parcel will be classified as land held for future development. We generally will not commence new development projects for aboveground vertical construction of new laboratory space without first securing significant pre-leasing for such space.

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The net book value of investments in real estate

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The net book value of rental properties.

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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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Carrying amount of land available for development.

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

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-Publisher SEC
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The carrying amount of investments in unconsolidated real estate and other joint ventures not separately presented. This includes direct and indirect investments.

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Carrying amount of income producing properties held for rental.

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