Secured and unsecured senior debt Narratives (Details) (USD $) In Thousands, unless otherwise specified		0 Months Ended
	Jun. 30, 2014 Greater Boston market Equity Method Investee	Jan. 31, 2014 Alexandria Technology Square Secured Debt from Insurance Company Maturing on 1 April 2014	Jun. 30, 2014 Construction Loans
Debt Instrument [Line Items]
Outstanding Balance		$ 208,700	$ 123,775
Proceeds from Contributions from Affiliates		$ 20,900
Equity interest percentage (in percent)	27.50%