Investments in real estate (Details 2)	9 Months Ended	12 Months Ended
Sep. 30, 2012 sqft	Dec. 31, 2011 sqft
North America
Rental properties, net, construction in progress, and land held for (future value-added projects)
Square feet undergoing preconstruction activities (in square feet)	2,400,000	2,700,000
Square feet of developable property (in square feet)	5,500,000	4,800,000
Alexandria Center for Life Science-New York City
Rental properties, net, construction in progress, and land held for (future value-added projects)
Square feet undergoing preconstruction activities (in square feet)	419,806
Alexandria Center at Kendall Square in East Cambridge, Massachusetts
Rental properties, net, construction in progress, and land held for (future value-added projects)
Square feet undergoing preconstruction activities (in square feet)	1,600,000
Number of largest projects included in preconstruction	2

The amount of square footage related to real estate 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.

No definition available.

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