Investments in real estate, net Acquisitions (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 27, 2014 Greater Boston, Massachusetts 225 Second Avenue sqft	Jan. 30, 2014 San Diego, California 3545 Cray Court sqft	Mar. 17, 2014 San Diego, California 4025/4031/4045 Sorrento Valley Boulevard property sqft	Mar. 31, 2014 Secured Debt Maturing on January 2023 San Diego, California 3545 Cray Court	Mar. 31, 2014 Secured Debt Maturing On 15 April 2016
Business Acquisition [Line Items]
Area of real estate property			112,500	116,556	42,566
Payments to acquire real estate property			$ 16,300,000	$ 64,000,000	$ 12,400,000
Average percentage of occupied properties				100.00%	100.00%
Assumption of secured notes payable in connection with purchase of properties	$ (48,329,000)	$ 0		$ 40,700,000	$ 7,600,000
Number of real estate properties					3
Stated interest rate (as a percent)						4.66%	5.74%