Name:	fsp_AmortizationOfFiniteLivedIdentifiableIntangibleAssetLiabilityNet
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No definition available.

Name:	fsp_DeferredLeasingCommissionsFutureAmortizationExpenseAbstract
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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
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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
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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
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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
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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
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Data Type:	xbrli:monetaryItemType
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No definition available.

Name:	fsp_DerivativeInstrumentsAbstract
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Balance Type:	na
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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.

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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
Period Type:	duration

No definition available.

Name:	us-gaap_DeferredCostsLeasingNetAbstract
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No definition available.

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

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-Name Accounting Standards Codification
-Topic 815
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-Section 45
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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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
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-Section 50
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-Publisher FASB
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-Name Accounting Standards Codification
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Amount of amortization expense for right-of-use asset from operating lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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Name:	us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense
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No definition available.

Name:	us-gaap_RevenueRecognitionAbstract
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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.

Name:	us-gaap_StraightLineRentAdjustments
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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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
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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.