Related Party Transactions (Details) - USD ($)			6 Months Ended
	Aug. 14, 2012	Dec. 27, 2007	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Related party transactions
Common Stock, shares issued (in shares)			1		1
Common Stock, shares outstanding (in shares)			1		1
Franklin Street
Related party transactions
Number of shares of preferred stock purchased by the related party		965.75
Percentage of issued preferred stock purchased by related party		43.70%
Percentage of outstanding preferred stock purchased by related party		43.70%
Consideration paid by related party for purchase of preferred stock		$ 82,813,000
Common Stock, shares issued (in shares)			1		1
Common Stock, shares outstanding (in shares)			1		1
FSP Property Management LLC
Related party transactions
Percentage of gross revenues of property			0.50%
Management fees paid			$ 44,000	$ 37,000
FSP Property Management LLC | Minimum
Related party transactions
Notice period for termination of agreement			30 days
FSP Investments LLC
Related party transactions
Notice period for termination of agreement	30 days
Monthly service fees payable under the agreement			$ 500
Service fees and expenses paid			$ 7,900	$ 7,300