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v3.21.1

Subsequent Events - Additional Information (Details) - Subsequent Event - Disposition Activity $ in Thousands | 1 Months Ended
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Apr. 22, 2021 USD ($) Property
Subsequent Event [Line Items] |
Number of Land Parcels | Property | 1
Proceeds From Sale Of Land Parcels | $ | $ 11,000

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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

X
- Definition Proceeds From Sale Of Land Parcels + References No definition available. + Details
Name: | fr_ProceedsFromSaleOfLandParcels
Namespace Prefix: | fr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | fr_InvestmentinRealEstateActivityAxis=fr_DispositionActivityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |