Organization, Basis of Presentation, Real Estate and Depreciation, Lease Acquisition Costs, Financial Instruments, Recent Accounting Standards, Derivative Instruments, and Fair Value Measurements (Details) (USD $)	0 Months Ended	6 Months Ended		12 Months Ended	6 Months Ended
	Feb. 29, 2012	Jun. 30, 2014 item sqft	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Building [Member]	Jun. 30, 2014 Building Improvements [Member] Minimum [Member]	Jun. 30, 2014 Building Improvements [Member] Maximum [Member]	Jun. 30, 2014 Furniture And Fixtures [Member] Minimum [Member]	Jun. 30, 2014 Furniture And Fixtures [Member] Maximum [Member]	Jun. 30, 2014 Franklin Street Properties Corp [Member]	Jan. 31, 2007 F S P Investments L L C [Member]
Organization, Basis of Presentation, Real Estate and Depreciation, Lease Acquisition Costs, Financial Instruments, Recent Accounting Standards, Derivative Instruments, and Fair Value Measurements
Number of stories of multi-tenant office and retail building		12
Rentable area of office and retail space (in square feet)		498,768
Organization
Common Stock, par value (in dollars per share)		$ 0.01		$ 0.01						$ 0.01
Preferred stock, underwritten shares issued (in shares)											700
Preferred stock, par value of underwritten shares (in dollars per share)											$ 0.01
Real Estate and Depreciation
Estimated useful lives					39 years	15 years	39 years	5 years	7 years
Impairment charges		$ 0		$ 0
Lease acquisition costs
Payments of lease acquisition costs	23,950,000
Amortization of lease incentive payments		$ 666,000	$ 665,000

FSP 50 South Tenth Street Corp 10-Q