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Variable Interest Entities - Additional Information (Details) - Joint Venture $ in Thousands | 9 Months Ended
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Sep. 30, 2018 USD ($) Property
Variable Interest Entity [Line Items] |
Number of Acres | Property | 532
Purchase price | $ | $ 49,000
Equity Method Investment, Ownership Percentage | 49.00%

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

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- Definition The amount of assets acquired. + References No definition available. + Details
Name: | fr_PurchasePrice
Namespace Prefix: | fr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=fr_JointVentureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |