Fair value of all asset derivatives designated as cash flow hedging instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

+ Details

Name:	us-gaap_CashFlowHedgeDerivativeInstrumentAssetsAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of all liability derivatives designated as cash flow hedging instruments.

+ References

+ Details

Name:	us-gaap_CashFlowHedgeDerivativeInstrumentLiabilitiesAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fr_InterestRateSwapTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fr_InterestRateSwapThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=fr_InterestRateSwapOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivatives - Fair Value Measurements on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
2021 Swaps
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	$ 19,137	$ 1,341
2021 Swaps \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	0	0
2021 Swaps \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	19,137	1,341
2021 Swaps \| Fair Value, Measurements, Recurring \| Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	0	0
2022 Swaps
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	20,793
2022 Swaps \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	0
2022 Swaps \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	20,793
2022 Swaps \| Fair Value, Measurements, Recurring \| Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Asset, Fair Value	$ 0
2015 Swaps
Derivatives, Fair Value [Line Items]
Hedging Instrument, Liability, Fair Value		(2,668)
2015 Swaps \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Liability, Fair Value		0
2015 Swaps \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Liability, Fair Value		(2,668)
2015 Swaps \| Fair Value, Measurements, Recurring \| Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Hedging Instrument, Liability, Fair Value		$ 0