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Investment in Real Estate Quantitative Information About Level 3 Fair Value Measurements (Details) $ in Thousands, ft² in Millions | Mar. 31, 2018 USD ($) ft² Property
--- | ---
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Number of industrial properties | 485
Gross leasable area (GLA) of industrial properties | ft² | 60.1
Unobservable Inputs (Level 3) | Contracted Price |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Fair Value of Industrial Property | $ | $ 6,416
Number of industrial properties | 1
Number of land parcels | 1
Gross leasable area (GLA) of industrial properties | ft² | 0.1

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- Definition Number of Land Parcels + References No definition available. + Details
Name: | fr_NumberofLandParcels
Namespace Prefix: | fr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Area of a real estate property. + References No definition available. + Details
Name: | us-gaap_AreaOfRealEstateProperty
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
Name: | us-gaap_AssetsFairValueDisclosureNonrecurring
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfRealEstateProperties
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ValuationTechniqueAxis=fr_ContractedPriceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |