Investment in Real Estate - Additional Information (Details) ft² in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($) ft² Property	Sep. 30, 2019 USD ($) ft² Property	Sep. 30, 2018 USD ($) Property
Real Estate Properties [Line Items]
Number of industrial properties	459	459
Gross leasable area (GLA) of industrial properties \| ft²	62,700	62,700
Acquisition Activity
Real Estate Properties [Line Items]
Number of industrial properties	8	8
Gross leasable area (GLA) of industrial properties \| ft²	500	500
Number of Land Parcels	8	8
Held for Sale Activity
Real Estate Properties [Line Items]
Number of industrial properties	1	1
Gross leasable area (GLA) of industrial properties \| ft²	40	40
Disposition Activity
Real Estate Properties [Line Items]
Number of industrial properties	10	10
Gross leasable area (GLA) of industrial properties \| ft²	1,700	1,700
Proceeds from sale of industrial properties \| $		$ 106,127
Gain on sale of real estate \| $		$ 44,772
Joint Venture \| Acquisition Activity
Real Estate Properties [Line Items]
Number of Land Parcels	1	1
Joint Venture \| Disposition Activity
Real Estate Properties [Line Items]
Number of Land Parcels	3	3	1
Sales Type Lease
Real Estate Properties [Line Items]
Gross leasable area (GLA) of industrial properties \| ft²	600	600
Sales-type Lease, Selling Profit (Loss) \| $	$ 8,606	$ 8,606	$ 0

Number of Land Parcels

No definition available.

Name:	fr_NumberofLandParcels
Namespace Prefix:	fr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

+ Details

Name:	us-gaap_GainLossOnSaleOfProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

- Definition

The cash inflow from sale of buildings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfBuildings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Amount of profit (loss) recognized at commencement from sales-type lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 5
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=119202524&loc=SL77919372-209981

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 6A
-URI http://asc.fasb.org/extlink&oid=118952077&loc=SL77927221-108306

+ Details

Name:	us-gaap_SalesTypeLeaseSellingProfitLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	fr_InvestmentinRealEstateActivityAxis=fr_AcquisitionActivityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	fr_InvestmentinRealEstateActivityAxis=fr_Fr_HeldForSaleActivityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	fr_SalesTypeLeaseAxis=fr_SalesTypeLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: