Accounts payable, accrued expenses, and tenant security deposits (Details) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2015 USD ($) ft²	Sep. 30, 2015 USD ($) ft²	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Accounts Payable and Other Accrued Liabilities		$ 143,556	$ 143,556		$ 127,828
Construction Payable		83,805	83,805		91,110
Acquired below market leases		27,072	27,072		8,810
Asset Retirement Obligation		7,828	7,828		9,108
Deferred Rent Liability		27,300	27,300		36,231
Derivative Liability		8,679	8,679		909
Prepaid Rent and Tenant Security Deposits		209,584	209,584		193,699
Other Accounts Payable and Accrued Liabilities	[1]	78,770	78,770		21,390
Accounts Payable and Accrued Liabilities		$ 586,594	586,594		$ 489,085
Payable for purchase of noncontrolling interest			$ 51,887	$ 0
Area of Real Estate Property | ft²		19,943,739	19,943,739
Alexandria Technology Square [Member]
Payable for purchase of noncontrolling interest		$ 54,000	$ 108,300
Alexandria Technology Square [Member]
Area of Real Estate Property | ft²		1,181,635	1,181,635

[1] Balance as of September 30, 2015. includes a $54.0 million liability related to the second installment payment for our acquisition of the remaining noncontrolling interest in our 1.2 million RSF campus at Alexandria Technology Square®. For additional information, refer to Note 11 – “Noncontrolling Interests” to our unaudited consolidated financial statements under Item 1 of this report.