Investments in real estate, net Schedule of investment in real estates (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Real Estate Properties [Line Items]
Land (related to rental properties)	$ 553,388		$ 522,664
Buildings and building improvements	5,714,673		4,933,314
Other improvements	174,147		189,793
Rental properties	6,442,208		5,645,771
Less: accumulated depreciation	(952,106)		(875,035)
Rental properties, net	5,490,102		4,770,736
Construction in progress ("CIP")/current value-added projects:
Investments in real estate, net	6,776,914		6,424,578
Construction in progress ("CIP")/current value-added projects:
Construction in progress ("CIP")/current value-added projects:
Development in process	628,266		842,179
Active development in North America | North America
Construction in progress ("CIP")/current value-added projects:
Development in process	511,838		431,578
Investment in unconsolidated joint venture
Construction in progress ("CIP")/current value-added projects:
Development in process	46,644	[1]	28,656	[1]
Active redevelopment in North America | North America
Construction in progress ("CIP")/current value-added projects:
Development in process	8,856		199,744
Active development and redevelopment in Asia | Asia
Construction in progress ("CIP")/current value-added projects:
Development in process	60,928		101,602
Generic infrastructure/building improvement projects in North America | North America
Construction in progress ("CIP")/current value-added projects:
Development in process	0		80,599	[2]
Land/future value-added projects:
Area of real estate property			205,164
Number of Projects Undergoing Improvements			8
Land/future value-added projects:
Land/future value-added projects:
Land available for development	658,546		811,663
Land undergoing predevelopment activities (CIP) in North America (2) | North America
Land/future value-added projects:
Land available for development	367,225		433,310
Land held for future development in North America | North America
Land/future value-added projects:
Land available for development	191,127		296,039
Land held for future development/undergoing predevelopment activities (CIP) in Asia | Asia
Land/future value-added projects:
Land available for development	77,251		82,314
Land subject to sale negotiations
Land/future value-added projects:
Land available for development	22,943		0
Rental properties, net and Construction in progress ("CIP")/current value-added projects
Construction in progress ("CIP")/current value-added projects:
Investments in real estate, net	$ 6,118,368		$ 5,612,915

[1] The book value for this unconsolidated joint venture represents our equity investment in the 360 Longwood Avenue development project.

[2] Includes the book value associated with 205,164 square feet at eight projects undergoing construction of generic laboratory/office improvements as of December 31, 2012, which were delivered during the year ended December 31, 2013.