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Stockholders’ Equity of the Company and Partners' Capital of the Operating Partnership - Additional Information (Details) - ATM [Member] $ in Thousands | Feb. 14, 2020 USD ($) shares
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Class of Stock [Line Items] |
Shares of company stock issuable under an at-the-market offering | shares | 14,000,000
Aggregate Gross Sale Proceeds | $ | $ 500,000

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- Definition The aggregate offering price of the distribution agreement for the at-the-market offering. + References No definition available. + Details
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Namespace Prefix: | fr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Saleable company common stock. + References No definition available. + Details
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Namespace Prefix: | fr_
Data Type: | xbrli:sharesItemType
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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=fr_AtmMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |