Name:	fsp_AmortizationOfFiniteLivedIdentifiableIntangibleAssetLiabilityNet
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseAbstract
Namespace Prefix:	fsp_
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The amount of amortization expense expected to be recognized for the remainder of deferred leasing commissions useful life after the fifth succeeding fiscal year.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseAfterYearFive
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
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The amount of amortization of deferred leasing commissions expected to be recognized during the year five of the five succeeding fiscal years.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseYearFive
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
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The amount of amortization of deferred leasing commissions expected to be recognized during the year four of the five succeeding fiscal years.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseYearFour
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The amount of amortization of deferred leasing commissions expected to be recognized during the year one of the five succeeding fiscal years.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseYearOne
Namespace Prefix:	fsp_
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The amount of amortization of deferred leasing commissions expected to be recognized during the year three of the five succeeding fiscal years.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseYearThree
Namespace Prefix:	fsp_
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The amount of amortization of deferred leasing commissions expected to be recognized during the year two of the five succeeding fiscal years.

No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseYearTwo
Namespace Prefix:	fsp_
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No definition available.

Name:	fsp_DerivativeInstrumentsAbstract
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Represents lease revenue excluding tenant reimbursable expenses straight line rent adjustments and amortization of favorable and unfavorable leases.

No definition available.

Name:	fsp_OperatingLeasesLeaseRevenueExcludingReimbursableExpensesStraightLineRentAdjustmentsAndAmortization
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Data Type:	xbrli:monetaryItemType
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Represents revenue from allowable charges due a landlord from its tenant.

No definition available.

Name:	fsp_RevenueFromTenantReimbursements
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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This element represents the amortization of deferred leasing fees incurred by the lessor and amortized over the term of the lease. Such fees represent (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction.

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-Section 45
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Name:	us-gaap_AmortizationOfDeferredLeasingFees
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No definition available.

Name:	us-gaap_DeferredCostsLeasingNetAbstract
Namespace Prefix:	us-gaap_
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No definition available.

Name:	us-gaap_EarningsPerShareAbstract
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Data Type:	xbrli:stringItemType
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Net fair value of all derivative instruments designated as fair value hedging instruments.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
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Data Type:	xbrli:integerItemType
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Period Type:	duration

Present value of lessee's discounted obligation for lease payments from operating lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
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-Subparagraph (b)
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Amount of lessee's right to use underlying asset under operating lease.

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-Publisher FASB
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Name:	us-gaap_OperatingLeaseRightOfUseAsset
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The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

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Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

No definition available.

Name:	us-gaap_RevenueRecognitionAbstract
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Period Type:	duration

No definition available.

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Amount of the adjustment to rental revenues to measure escalating leasing revenues on a straight line basis.

No definition available.

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment
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Data Type:	xbrli:sharesItemType
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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

No definition available.