Investments in real estate, net Schedule of investment in real estates (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Real Estate Properties [Line Items]
Land	$ 679,070us-gaap_Land	$ 624,681us-gaap_Land
Rental properties	7,509,763us-gaap_RentalProperties	6,988,313us-gaap_RentalProperties
Land/future value-added projects:
Land available for development	497,989us-gaap_LandAvailableForDevelopment	683,101us-gaap_LandAvailableForDevelopment
Real Estate Investment Property, at Cost	8,421,861	8,228,855
Less: accumulated depreciation	(1,153,830)	(1,120,245)
Equity Method Investments	120,028us-gaap_EquityMethodInvestments	117,406us-gaap_EquityMethodInvestments
Real Estate Investments Property, including Unconsolidated Joint Ventures, at Cost	8,541,889	8,346,261
Investments in real estate, net	7,388,059us-gaap_RealEstateInvestmentPropertyNet	7,226,016us-gaap_RealEstateInvestmentPropertyNet
Investment Building and Building Improvements	6,609,158	6,171,504
Improvements Others	221,535are_ImprovementsOthers	192,128are_ImprovementsOthers
Construction in progress ("CIP")/current value-added projects:
Construction in progress ("CIP")/current value-added projects:
Development in process	414,109	557,441
Active development in North America \| North America [Member]
Construction in progress ("CIP")/current value-added projects:
Development in process	361,182	500,894
Active redevelopment in North America \| North America [Member]
Construction in progress ("CIP")/current value-added projects:
Development in process	52,927	42,482
Active development and redevelopment in Asia \| Asia [Member]
Construction in progress ("CIP")/current value-added projects:
Development in process	0	14,065
Current, Near-Term and Future Value-Creation Projects [Member]
Land/future value-added projects:
Real Estate Investment Property, at Cost	7,923,872	7,545,754
Land undergoing predevelopment activities (CIP) in North America (2)
Land/future value-added projects:
Land available for development	227,644	429,378
Land held for future development in North America
Land/future value-added projects:
Land available for development	270,345	253,723
Land held for future development in North America \| North America [Member]
Land/future value-added projects:
Land available for development	190,407	175,175
Land held for future development in North America \| Asia [Member]
Land/future value-added projects:
Land available for development	79,938	78,548
Current, Near-Term and Future Value-Creation Projects [Member]
Land/future value-added projects:
Real Estate Investment Property, at Cost	912,098	1,240,542
50, 60, and 100 Binney Street Project [Member] \| Land undergoing predevelopment activities (CIP) in North America (2) \| North America [Member]
Land/future value-added projects:
Land available for development	130,475	321,907
Other Projects in North America [Member] \| Land undergoing predevelopment activities (CIP) in North America (2) \| North America [Member]
Land/future value-added projects:
Land available for development	$ 97,169	$ 107,471

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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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Real Estate Investments Property, including Unconsolidated Joint Ventures, at Cost

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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 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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Carrying amount of income producing properties held for rental.

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