Document and Entity Information Area of Land Acres of land (in acres) Off Market Lease Favorable Net Acquired favorable real estate leases, net of accumulated amortization of $419 and $371, respectively 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. Acquired favorable real estate leases, accumulated amortization (in dollars) 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. Off Market Lease Favorable Accumulated Amortization Acquired unfavorable real estate leases, accumulated amortization (in dollars) Unfavorable Real Estate Leases, Accumulated Amortization The amount of accumulated amortization related to unfavorable real estate leases. Weighted Average Number of Preferred Shares Outstanding Basic and Diluted Weighted average number of preferred shares outstanding, basic and diluted (in shares) The average number of preferred shares or units issued and outstanding that are used in calculating basic and diluted EPS. Earnings Per Preferred Share, Basic and Diluted Net income (loss) per preferred share, basic and diluted (in dollars per share) The amount of net income or loss per each share of the preferred stock outstanding, during the reporting period. 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. Amortization Unfavorable Real Estate Leases Amortization of unfavorable real estate leases 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. Retained Earnings and Distributions in Excess of Earnings [Member] Retained Earnings 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). Number of Stories Number of stories in multi-tenant office tower Represents the number of stories in the real estate property. Amendment Description Organization and Basis of Presentation [Table] Represents the details pertaining to organization and its business. Amendment Flag Franklin Street Properties Corp [Member] Franklin Street Details pertaining to Franklin Street Properties Corp., which holds the sole share of the entity's common stock. FSP Investments LLC [Member] FSP Investments LLC Details pertaining to FSP Investments LLC which is a wholly-owned subsidiary of Franklin Street Properties Corp. Organization and Basis of Presentation [Line Items] Organization and basis of presentation Statute of limitation period for income tax returns Income Tax Returns Limitation Period Represents the limitation period for the income tax returns filed by the entity. FSP Property Management LLC [Member] FSP Property Management LLC Details pertaining to FSP Property Management LLC which is the wholly-owned subsidiary of Franklin Street Properties Corp. Revolving Credit Facility before Amendment [Member] Phoenix Revolver before amendments Represents the revolving credit facility before amendments. Notice Period for Agreement Termination Notice period for termination of agreement Represents the notice period required for termination of asset management agreement with related party. Debt Instrument Term Debt instrument term Represents the term of debt instrument. Line of Credit Facility Draw Fee Draw fee (as a percent) The draw fee, expressed in basis points, charged for each advance under the line of credit facility. Line of Credit Facility Draw Fee, Amount Draw fees Represents the draw fees incurred during the period on line of credit facility. Related Party Transaction Purchase of Preferred Stock by Related Party Number of shares of preferred stock purchased by the related party Represents the number of shares of preferred stock of the entity purchased by the related party. Related Party Transaction Purchase of Preferred Stock by Related Party Consideration Paid Consideration paid by related party for purchase of preferred stock Represents the consideration paid by the related party for the preferred stock of the entity. Schedule of Dividends Paid [Table Text Block] Schedule of distributions declared and paid by the Company Tabular disclosure of dividend declared and paid by the entity during the reporting period. Related Party Transactions Stock Issued to Related Party [Abstract] Related Party Transactions-Preferred Stock 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. Current Fiscal Year End Date Document Period End Date 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 Expenses Accounts Payable and Accrued Liabilities Disclosure [Text Block] Document Fiscal Year Focus Document Fiscal Period Focus Legal Entity [Axis] Document Type Accounts Receivable, Net Tenant rent receivables, less allowance for doubtful accounts of $4 and $4, respectively Accounts Payable and Accrued Liabilities Accounts payable and accrued expenses Retained earnings and distributions in excess of earnings Accumulated Distributions in Excess of Net Income 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 operating activities: Allowance for Doubtful Accounts Receivable Tenant rent receivables, allowance for doubtful accounts (in dollars) Assets [Abstract] Assets: Assets Total assets Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Building Improvements [Member] Building Improvements Building [Member] Building 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, beginning of period Cash and cash equivalents, end of period Cash and cash equivalents Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Disclosure of non-cash investing activities: Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Commitments and Contingencies Commitments and Contingencies. Common Stock Common Stock [Member] Common Stock, Shares, Outstanding Common Stock, share outstanding Common Stock, Value, Issued Common Stock, $.01 par value, 1 share authorized, issued and outstanding Common Stock, Shares, Issued Common Stock, share issued Common Stock, Par or Stated Value Per Share Common Stock, par value (in dollars per share) Common Stock, Shares Authorized Common Stock, share authorized Cost of Real Estate Revenue Rental operating expenses Costs and Expenses [Abstract] Expenses: Costs and Expenses Total expenses Debt Instrument, Description of Variable Rate Basis Debt, interest rate basis Debt Instrument, Basis Spread on Variable Rate Basis points added to reference rate (as a percent) Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Interest Rate at Period End Effective interest rate at end of period (as a percent) Debt Instruments [Abstract] Debt Deferred Rent Receivables, Net Step rent receivable Deferred Costs, Leasing, Net Deferred leasing costs, net of accumulated amortization of $1,612 and $1,341, respectively Deferred Costs, Leasing, Accumulated Amortization Deferred leasing costs, accumulated amortization (in dollars) Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Depreciation, Depletion and Amortization Depreciation and amortization Distribution declared Dividend Declared [Member] Distributions - preferred stockholders or $2,712 and $3,723 per preferred share for the years ended 2011 and 2010, respectively Dividends, Preferred Stock, Cash Dividends [Axis] Dividends [Domain] Due to Affiliate Loan payable - affiliate Earnings Per Share [Text Block] Net Income Per Share Net Income Per Share Cash Distributions Equity Component [Domain] Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Acquired real estate leases, accumulated amortization (in dollars) Finite-Lived Intangible Assets, Accumulated Amortization Acquired real estate leases, net of accumulated amortization of $1,195 and $1,059, respectively Finite-Lived Intangible Assets, Net Fixtures and Equipment, Gross Furniture and fixtures Furniture and Fixtures [Member] Furniture and Equipment Consolidated Statements of Operations Income Tax Disclosure [Text Block] Income Taxes Income Taxes Increase (Decrease) in Deferred Leasing Fees Payment of deferred leasing costs Increase (Decrease) in Due to Related Parties Proceeds from loan payable - affiliate Increase (Decrease) in Accounts Receivable Tenant rent receivables 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 Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Interest Expense Interest expense Interest Paid Cash paid for interest Interest expense paid Investment Income, Interest Interest income Investment Building and Building Improvements Building and improvements Land Land 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 Revolving credit facility, maximum principal amount Line of Credit Facility, Amount Outstanding Advances drawn and outstanding under the Phoenix Revolver Management Fee, Amount Paid Management fees paid Maximum [Member] Maximum Minimum [Member] Minimum 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 operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Cash flows from operating activities: Net increase (decrease) in cash and cash equivalents Net Cash Provided by (Used in) Continuing Operations Net increase (decrease) in cash and cash equivalents Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net cash used for investing activities Net Rentable Area Rentable square feet of office and retail space Net Cash Provided by (Used in) Financing Activities, Continuing Operations Net cash provided by 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) Number of reportable segments Number of Reportable Segments Off-market Lease, Unfavorable Acquired unfavorable real estate leases, net of accumulated amortization of $492 and $436, respectively Operating Income (Loss) Net income (loss) before interest income Organization, Basis of Presentation, Real Estate and Depreciation, and Financial Instruments Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Organization, Basis of Presentation, Real Estate and Depreciation, and Financial Instruments Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Organization Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Accounts Payable and Accrued Expenses Payments of Ordinary Dividends, Preferred Stock and Preference Stock Distributions to stockholders Total Distributions Payments to Acquire Real Estate Purchase of real estate assets Preferred Stock, Value, Issued Preferred Stock, $.01 par value, 1,050 shares authorized, issued and outstanding at September 30, 2012 and December 31, 2011, aggregate liquidation preference $105,000 Preferred Stock, Shares Authorized Preferred Stock, shares authorized 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 Preferred Stock, Par or Stated Value Per Share Preferred Stock, par value (in dollars per share) Preferred Stock, aggregate liquidation preference (in dollars) Preferred Stock, Liquidation Preference, Value Preferred Stock, Shares Outstanding Preferred Stock, shares outstanding Preferred Stock Preferred Stock [Member] Prepaid Expense and Other Assets Prepaid expenses and other assets Property, Plant and Equipment, Useful Life Estimated useful lives Property, Plant and Equipment, Type [Domain] Property Management Fee, Percent Fee Percentage of gross revenues of property Property, Plant and Equipment [Abstract] Real Estate and Depreciation Schedule of estimated useful lives of real estate assets Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment, Type [Axis] Provision for Doubtful Accounts Decrease in bad debt reserve Range [Axis] Range [Domain] SCHEDULE III Real Estate and Accumulated Depreciation SCHEDULE III Real Estate and Accumulated Depreciation Real Estate and Accumulated Depreciation Disclosure [Text Block] 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 Less accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Real Estate Taxes and Insurance Real estate taxes and insurance Real Estate Revenue, Net Rental Real Estate and Depreciation Real Estate, Policy [Policy Text Block] Related Party Transactions Disclosure [Text Block] Related Party Transactions Related Party Transaction [Line Items] Related party transactions Related Party [Domain] Related Party Transactions Related Party [Axis] Revenues Total revenue Revenues [Abstract] Revenues: Phoenix Revolver Revolving Credit Facility [Member] Straight Line Rent Step rent receivable Step rent receivable Scenario, Unspecified [Domain] Schedule of Related Party Transactions, by Related Party [Table] Security Deposit Liability Tenant security deposits Segment Reporting Segment Reporting Disclosure [Text Block] Segment Reporting Statement [Table] Acquired unfavorable real estate leases, accumulated amortization Scenario [Axis] Statement [Line Items] Statement Consolidated Statements of Changes in Stockholders' Equity Consolidated Statements of Cash Flows Equity Components [Axis] Consolidated Balance Sheets Stockholders' Equity Attributable to Parent [Abstract] Stockholders' Equity: Stockholders' Equity Attributable to Parent Total Stockholders' Equity Balance Balance Stockholders' Equity Note [Abstract] Cash Distributions Stockholders' Equity Note Disclosure [Text Block] Stockholders' Equity, Period Increase (Decrease) Subsequent Events [Text Block] Subsequent Event Subsequent Event Subsequent Event Type [Domain] Subsequent events Subsequent Event [Line Items] Subsequent Event Type [Axis] Subsequent Event [Table] Subsequent events Subsequent Event [Member] Supplemental Cash Flow Information [Abstract] Supplemental disclosure of cash flow information: Common Stock, Shares Issued and Outstanding Common Stock, shares issued and outstanding Number of common shares of the 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. Investor Service Fees Service fees paid Represents the service fees paid under the agreement.