Document and Entity Information Acquired favorable real estate leases, net of accumulated amortization of $1,841 and $1,794, respectively Off Market Lease, Favorable Net Acquired favorable real estate leases, net This element represents the identifiable intangible asset established upon acquisition, based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date, less accumulated amortization and any impairment charges. Lease Inducements Net Lease acquisition costs, net The unamortized carrying amount of lease inducement costs as of the balance sheet date. Amounts are amortized against rental revenue over the term of the lease. Off Market Lease, Favorable Accumulated Amortization The accumulated amount of amortization of the identifiable intangible asset established upon acquisition, based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date. Acquired favorable real estate leases, accumulated amortization Acquired unfavorable real estate leases, accumulated amortization Unfavorable Real Estate Leases Accumulated Amortization The amount of accumulated amortization related to unfavorable real estate leases. The average number of preferred shares or units issued and outstanding that are used in calculating basic and diluted EPS. Weighted Average Number of Preferred Shares Outstanding, Basic and Diluted Weighted average number of preferred shares outstanding, basic and diluted (in shares) Earnings Per Preferred Share, Basic and Diluted The amount of net income or loss per each share of the preferred stock outstanding, during the reporting period. Net income (loss) per preferred share, basic and diluted (in dollars per share) Amortization Favorable Real Estate Leases Amortization of favorable real estate leases The aggregate expense charged against earnings to allocate the asset associated with the acquisition of an above-market lease when the terms of the lease are favorable to the market terms for the lease at the date of acquisition in a systematic and rational manner to the periods expected to be impacted from such asset. As a noncash expense, this element is added back to net income when calculating cash provided by (used in) operations using the indirect method. The aggregate expense charged against earnings to allocate the liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition in a systematic and rational manner to the periods expected to be impacted from such liability. As a noncash expense, this element is deducted from net income when calculating cash provided by (used in) operations using the indirect method. Amortization Unfavorable Real Estate Leases Amortization of unfavorable real estate leases Lease Inducements Period Increase (Decrease) Payments of lease acquisition costs The net increase or decrease in the unamortized balance of lease inducement costs for period. Payment of lease acquisition costs Amendment Description Disclosure of non-cash operating activities: Cash Flow Non Cash Operating Activities Disclosure [Abstract] Amendment Flag Cash Flow Non Cash Financing Activities Disclosure [Abstract] Disclosure of non-cash financing activities: Noncash Accrued Deferred Finance Costs Accrued deferred financing costs This element represents non cash deferred finance cost of entity as on reporting date. Retained Earnings and Distributions in Excess of Earnings [Member] Retained Earnings (Deficit) and Distributions in Excess of Earnings The cumulative amount of the reporting entity's undistributed earnings or deficit and the excess of retained earnings (or accumulated earnings) distributions to shareholders (or partners). Franklin Street Properties Corp [Member] Details pertaining to Franklin Street Properties Corp., which holds the sole share of the entity's common stock. Franklin Street FSP Investments LLC [Member] Details pertaining to FSP Investments LLC which is a wholly-owned subsidiary of Franklin Street Properties Corp. FSP Investments LLC FSP Property Management LLC [Member] Details pertaining to FSP Property Management LLC which is the wholly-owned subsidiary of Franklin Street Properties Corp. FSP Property Management LLC Income Tax Returns Limitation Period Represents the limitation period for the income tax returns filed by the entity. Statute of limitation period for income tax returns Notice Period for Agreement Termination Represents the minimum notice period required for the termination of asset management agreement with the related party. Notice period for termination of agreement, minimum Number of Stories Represents the number of stories of multi-tenant office tower. Number of stories of multi-tenant office tower Organization and Basis of Presentation [Line Items] Organization, basis of presentation and real estate and depreciation Organization and Basis of Presentation [Table] Represents the details pertaining to organization and its business. Schedule of Dividends Paid [Table Text Block] Tabular disclosure of dividend declared and paid by the entity during the reporting period. Schedule of distributions declared and paid by the Company Lease Acquisition Costs [Abstract] Lease acquisition costs Line of Credit Facility Fee Revolving Advance Fee Percentage Fee for each revolving advance (as a percent) Represents the percentage of fee payable for each revolving advance under a revolving credit facility. Line of Credit Facility Fee Revolving Advance Fee Paid Revolving advance fee paid Represents the revolving advance fee paid by the entity during the reporting period. Debt Instrument Prepayment Covenant Minimum Partial Payment Minimum partial payment Represents the minimum partial payment to be made in case of prepayment as per the loan agreement. Current Fiscal Year End Date Debt Instrument, Exit Fee Percentage Exit fee (as a percent) Represents the fee payable on prepayment and upon payment on the maturity date, expressed as a percentage of such prepayment or payment of the unpaid principal balance. Preferred Stock, Underwritten Shares Issued Preferred stock, underwritten shares issued (in shares) Total number of underwritten nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt. Preferred Stock, Underwritten Par or Stated Value, Per Share Preferred stock, par value of underwritten shares (in dollars per share) Face amount or stated value per share of nonredeemable preferred stock underwritten (or preferred stock redeemable solely at the option of the issuer); generally not indicative of the fair market value per share. Debt Term Term of debt Represents the details pertaining to term of debt. Debt Instrument, Exit Fee Exit fee Represents the amount of exit fee paid in connection with the repayment of the unpaid principal balance on or before the maturity date. Senior Credit Facility [Member] Term loan Represents information pertaining to the secured credit facility entered into by the entity. Bank of America Amended and Restated Promissory Note [Member] BofA Note Represents information pertaining to the Amended and Restated Promissory Note executed and delivered with Bank of America, N.A., by the entity. RBS Citizens Amended and Restated Promissory Note [Member] RBS Citizens Note Represents information pertaining to the Amended and Restated Promissory Note executed and delivered with RBS Citizens, National Association, by the entity. Debt Instrument Variable Rate Base [Axis] The alternative reference rate that may be used to calculate the variable interest rate of the debt instrument. Debt Instrument Variable Rate Base [Domain] Identification of the reference rate that is used to calculate the variable interest rate of the debt instrument. Document Period End Date Debt Instrument Variable Rate LIBOR [Member] LIBOR The London Interbank Offered Rate (LIBOR) used to calculate the variable interest rate of the debt instrument. Debt Instrument Covenant Minimum Partial Payment Minimum partial payment Represents the minimum amount of partial payment for the debt instrument. Entity [Domain] Summary of Significant Accounting Policies Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Filer Category Entity Public Float Entity Registrant Name Entity Central Index Key Entity Common Stock, Shares Outstanding Accounts Payable and Accrued Liabilities Disclosure [Text Block] Accounts Payable and Accrued Expenses Document Fiscal Year Focus Document Fiscal Period Focus Legal Entity [Axis] Legal Entity [Axis] Document Type Accounts Receivable, Net Tenant rent receivable, less allowance for doubtful accounts of $0 and $51, respectively Accounts Payable and Accrued Liabilities Accounts payable and accrued expenses Accumulated Distributions in Excess of Net Income Retained earnings and distributions in excess of earnings Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated Amortization, Deferred Finance Costs Deferred financing costs, accumulated amortization Additional Paid in Capital Additional paid-in capital Additional Paid-in Capital Additional Paid-in Capital [Member] Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income (loss) to net cash provided by (used for) operating activities: Allowance for Doubtful Accounts Receivable Tenant rent receivable, allowance for doubtful accounts Amortization of Financing Costs Amortization expense Amortization of Lease Incentives Amortization of lease incentive payments Assets [Abstract] Assets: Assets Total assets Basis of Accounting, Policy [Policy Text Block] Basis of Presentation Bridge Loan [Member] Bridge Loan Building Improvements Building Improvements [Member] Building Building [Member] Capital Expenditures Incurred but Not yet Paid Accrued costs for purchase of real estate assets Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Disclosure of non-cash investing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Commitments and Contingencies. Commitments and Contingencies: Commitments and Contingencies Common Stock Common Stock [Member] Common Stock, Shares, Outstanding Common Stock, share outstanding (in shares) Common stock outstanding, held by related party Common Stock, Value, Issued Common Stock, $.01 par value, 1 share authorized, issued and outstanding Common Stock, Shares, Issued Common Stock, share issued (in shares) Common stock issued, held by related party Common Stock, Par or Stated Value Per Share Common Stock, par value (in dollars per share) Common Stock, Shares Authorized Common Stock, share authorized (in shares) Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Cost of Real Estate Revenue Rental operating expenses Costs and Expenses [Abstract] Expenses: Costs and Expenses Total expenses Variable interest rate basis Debt Instrument, Description of Variable Rate Basis Loan payable Debt Instrument [Line Items] Schedule of Long-term Debt Instruments [Table] Debt Instrument, Fee Amount Term Loan Component fee Debt Disclosure [Text Block] Loans Payable Loans Payable. Interest rate margin (as a percent) Debt Instrument, Basis Spread on Variable Rate Debt Instrument [Axis] Debt Instrument [Axis] Principal amount Debt Instrument, Face Amount Debt Instrument, Name [Domain] Debt Instrument, Increase, Additional Borrowings Amount funded Debt fixed interest rate (as a percent) Debt Instrument, Interest Rate, Stated Percentage Fixed rate of interest (as a percent) Interest rate (as a percent) Deferred Finance Costs, Net Deferred financing costs, net of accumulated amortization of $37 and $0, respectively Deferred Rent Receivables, Net Step rent receivable Deferred Costs, Leasing, Net Deferred leasing costs, net of accumulated amortization of $359 and $125, respectively Deferred Costs, Leasing, Accumulated Amortization Deferred leasing costs, accumulated amortization Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Depreciation, Depletion and Amortization Depreciation and amortization Financial Instruments: Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Financial Instruments: Derivatives and Hedging Strike Rate (as a percent) Derivative, Fixed Interest Rate Derivative Instruments Derivatives, Policy [Policy Text Block] Distribution declared Dividend Declared [Member] Distributions - preferred stockholders or $5,250 and $7,000 per preferred share for the years 2011 and 2010, respectively Dividends, Preferred Stock, Cash Dividends [Axis] Dividends [Axis] Dividends [Domain] Due to Affiliate Loan payable - affiliate Outstanding principal balance of loan Earnings Per Share [Text Block] Net Income Per Share Net Income Per Share Cash Distributions Equity Component [Domain] Repayment of Bridge Loan from Franklin Street Extinguishment of Debt, Amount Fair Value of Financial Instruments, Policy [Policy Text Block] Financial Instruments Financing [Domain] Financing [Axis] Acquired real estate leases, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Net Acquired real estate leases, net of accumulated amortization of $2,973 and $3,295, respectively Furniture and Equipment Furniture and Fixtures [Member] Consolidated Statements of Operations Income Tax Disclosure [Text Block] Income Taxes Income Taxes Income Taxes Increase (Decrease) in Deferred Leasing Fees Payments of deferred leasing costs Increase (Decrease) in Accounts Receivable Tenant rent receivable Increase (Decrease) in Accounts Payable and Accrued Liabilities Accounts payable and accrued expenses Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses and other assets Increase (Decrease) in Security Deposits Tenant security deposits Increase (Decrease) in Restricted Cash for Operating Activities Cash - held in escrow Cash - held in escrow Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Interest Expense Interest expense Interest expense for loan Interest Expense, Debt Interest Paid Cash paid for interest Interest expense paid Investment Income, Interest Interest income Investment Building and Building Improvements Building and improvements Land Land Lease, Policy [Policy Text Block] Lease Acquisition Costs Liabilities [Abstract] Liabilities: Liabilities Total liabilities Liabilities and Equity [Abstract] Liabilities and Stockholders' Equity: Liabilities and Equity Total Liabilities and Stockholders' Equity Line of Credit Facility, Maximum Borrowing Capacity Maximum borrowing capacity Line of Credit Facility, Increase, Additional Borrowings Revolving advance BofA Loan Loans Payable [Member] Interest-only loan Principal amount of loan Loans Payable Management fees paid Management Fee, Amount Paid Maximum Maximum [Member] Minimum Minimum [Member] Nature of Operations [Text Block] Organization Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Cash flows from financing activities: Net Cash Provided by (Used in) Operating Activities, Continuing Operations Net cash provided by (used for) operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Continuing Operations Net decrease in cash and cash equivalents Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net cash used for investing activities Rentable area of office and retail space (in square feet) Net Rentable Area Net Cash Provided by (Used in) Financing Activities, Continuing Operations Net cash provided by (used for) financing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Cash flows from investing activities: Net Income (Loss) Attributable to Parent Net income (loss) attributable to preferred stockholders Net income (loss) Notes Payable to Banks [Member] Interest-only loan Notional Value Notional Amount of Interest Rate Derivatives Number of reportable segments Number of Reportable Segments Off-market Lease, Unfavorable Acquired unfavorable real estate leases, net of accumulated amortization of $830 and $725, respectively Operating Income (Loss) Income (loss) before interest income Organization, Basis of Presentation, Real Estate and Depreciation, Lease Acquisition Costs, Financial Instruments, Derivative Instruments, and Fair Value Measurements Organization, Basis of Presentation, Real Estate and Depreciation, Lease Acquisition Costs, Financial Instruments, Derivative Instruments, and Fair Value Measurements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Organization, Basis of Presentation, Real Estate and Depreciation, and Financial Instruments Unrealized loss on derivative financial instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Deferred gains (losses) on derivative financial instruments Other comprehensive loss: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Total other comprehensive loss Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Accounts Payable and Accrued Expenses Payments of Ordinary Dividends, Preferred Stock and Preference Stock Total Distributions Distributions to stockholders Payments of Financing Costs Payments of deferred financing costs Costs and fees paid Payments to Acquire Real Estate Purchase of real estate assets Preferred Stock, Value, Issued Preferred Stock, $.01 par value, 1,540 shares authorized, 700 issued and outstanding at September 30, 2012 and December 31, 2011, aggregate liquidation preference $70,000 Preferred Stock, Shares Authorized Preferred Stock, shares authorized (in shares) Distribution declared per preferred share (in dollars per share) Preferred Stock, Dividends Per Share, Declared Preferred Stock, Dividends, Per Share, Cash Paid Distributions Per Preferred Share (in dollars per share) Preferred Stock, Shares Issued Preferred Stock, shares issued (in shares) Preferred Stock, Par or Stated Value Per Share Preferred Stock, par value (in dollars per share) Preferred Stock, Liquidation Preference, Value Preferred Stock, aggregate liquidation preference Preferred Stock, Shares Outstanding Preferred Stock, shares outstanding (in shares) Preferred Stock Preferred Stock [Member] Prepaid Expense and Other Assets Prepaid expenses and other assets Proceeds from Related Party Debt Proceeds from loan payable affiliate Estimated useful lives Property, Plant and Equipment, Useful Life Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Percentage of gross revenues of property Property Management Fee, Percent Fee Real Estate and Depreciation Property, Plant and Equipment [Abstract] Schedule of estimated useful lives of real estate assets Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Provision for Doubtful Accounts Increase (decrease) in bad debt reserve Range [Axis] Range [Axis] Range [Domain] Range [Domain] SCHEDULE III Real Estate and Accumulated Depreciation Real Estate and Accumulated Depreciation Disclosure [Text Block] SCHEDULE III Real Estate and Accumulated Depreciation Real Estate Investment Property, Net [Abstract] Real estate investments, at cost: Real Estate Investment Property, at Cost Real estate investments, gross Real Estate Investment Property, Net Real estate investments, net Real Estate Investment Property, Accumulated Depreciation Less accumulated depreciation Real Estate Taxes and Insurance Real estate taxes and insurance Real Estate Revenue, Net Rental Real Estate, Policy [Policy Text Block] Real Estate and Depreciation Refinancing of bridge loan Refinancing of Debt [Member] Related Party Transactions Disclosure [Text Block] Related Party Transactions Related party transactions Related Party Transaction [Line Items] Related Party [Domain] Related Party Transactions Related Party [Axis] Repayment of Debt [Member] Repayment of Bridge Loan Principal payments on long-term debt Repayments of Secured Debt Restricted Cash and Cash Equivalents Cash - held in escrow Revenues Total revenue Revenues [Abstract] Revenues: Revolving Credit Facility [Member] Bridge Loan - Revolving Line Component Straight Line Rent Step rent receivable Scenario, Unspecified [Domain] Schedule of notional and fair value of the entity's derivative financial instrument Schedule of Interest Rate Derivatives [Table Text Block] Schedule of Related Party Transactions, by Related Party [Table] Secured Debt [Member] Bridge Loan - Term Loan Component Secured Debt Loan payable Security Deposit Liability Tenant security deposits Segment Reporting Segment Reporting Segment Reporting Segment Reporting Disclosure [Text Block] Statement [Table] Scenario [Axis] Statement [Line Items] Statement Consolidated Statements of Changes in Stockholders' Equity Consolidated Statements of Cash Flows Equity Components [Axis] Consolidated Balance Sheets Consolidated Statements of Other Comprehensive Income (Loss) Stockholders' Equity Attributable to Parent [Abstract] Stockholders' Equity: Stockholders' Equity Attributable to Parent Total Stockholders' Equity Balance Balance Cash Distributions Stockholders' Equity Note Disclosure [Text Block] Stockholders' Equity, Period Increase (Decrease) Subsequent Event Subsequent Events [Text Block] Subsequent Event Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent events Subsequent Event [Line Items] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event [Table] Subsequent Event [Table] Subsequent event Subsequent Event [Member] Supplemental Cash Flow Information [Abstract] Supplemental disclosure of cash flow information: Proceeds from loan payable Proceeds from Issuance of Long-term Debt Principal payments on loan payable - affiliate Proceeds from (Repayments of) Related Party Debt Fair Value Measurement, Policy [Policy Text Block] Fair Value Measurements Interest rate, spread (as a percent) Debt Instrument, Interest Rate Increase Common Stock Shares Issued and Outstanding Common Stock, shares issued and outstanding Number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized and also includes number of shares of common stock outstanding. Monthly Investor Service Fees Monthly service fees payable under the agreement Represents the monthly service fees under the agreement and to reimburse for its reasonable out-of-pocket expenses incurred in connection with the agreement. Minimum Notice Period for Agreement Termination Minimum notice period for termination of agreement Represents the minimum notice period required for the termination of asset management agreement with the related party. Investor Service Fees Service fees paid Represents the service fees paid under the agreement. Derivative Liabilities Other Liabilities: derivative termination value Maximum Length of Time Hedged in Interest Rate Cash Flow Hedge Term for which interest rate is fixed Interest Rate Cash Flow Hedge Liability at Fair Value Fair Value Total Financing Fees Paid to Related Party Costs and fees paid Represents the total costs and fees associated with the debt instrument paid to a related party. Debt Instrument Fixed Rate Related Party Fixed rate of interest (as a percent) Represents the fixed interest rate paid to a related party on the debt instrument.