Number of key demand drivers.

No definition available.

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- Definition

Percentage of operating portfolio in which the entity serves as the developer.

+ References

No definition available.

+ Details

Name:	jbgs_PercentageOfOperatingPortfolio
Namespace Prefix:	jbgs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of subordinated interest held through an unconsolidated real estate venture.

+ References

No definition available.

+ Details

Name:	jbgs_SubordinatedOwnershipInterest
Namespace Prefix:	jbgs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of real estate property being developed by Virginia Tech.

+ References

No definition available.

+ Details

Name:	jbgs_ValueOfRealEstatePropertyBeingDevelopedByVirginiaTech
Namespace Prefix:	jbgs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of separate real estate development properties located on land subject to ground leases.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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 number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Details

Name:	srt_StatementGeographicalAxis=jbgs_NationalLandingVirginiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=jbgs_FutureDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_AssetUnderConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=jbgs_CommercialRealEstateOneBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=jbgs_CommercialRealEstateFourBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_WhollyOwnedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=jbgs_VirginiaTechMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=jbgs_JBGSmithLPMember
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Organization and Basis of Presentation - Narrative (Details) ft² in Millions, $ in Billions	9 Months Ended
	Sep. 30, 2025 USD ($) ft² item property building	Dec. 31, 2024 building
Organization and Basis of Presentation
Number of key demand drivers \| item	4
Number of Real Estate Properties	37
National Landing
Organization and Basis of Presentation
Percentage of operating portfolio by the entity	75.00%
Future Development
Organization and Basis of Presentation
Number of Real Estate Properties	19
Area of real estate property \| ft²	10.7
Multifamily
Organization and Basis of Presentation
Number of Real Estate Properties	14
Number of units in real estate property \| item	6,164
Multifamily \| Asset under Construction
Organization and Basis of Presentation
Number of Real Estate Properties	1
Number of units in real estate property \| item	355
Commercial Real Estate
Organization and Basis of Presentation
Number of Real Estate Properties	21
Area of real estate property \| ft²	7.0
One Commercial Building
Organization and Basis of Presentation
Subordinated interest	10.00%	10.00%
Number of Real Estate Properties \| building	1	1
Four Commercial Buildings
Organization and Basis of Presentation
Subordinated interest	33.50%
Number of Real Estate Properties \| building	4
Wholly Owned Properties
Organization and Basis of Presentation
Number of properties for ground lease	2
Wholly Owned Properties \| Future Development
Organization and Basis of Presentation
Area of real estate property \| ft²	8.7
Wholly Owned Properties \| Multifamily
Organization and Basis of Presentation
Number of units in real estate property \| item	5,978
Wholly Owned Properties \| Multifamily \| Asset under Construction
Organization and Basis of Presentation
Number of units in real estate property \| item	355
Wholly Owned Properties \| Commercial Real Estate
Organization and Basis of Presentation
Area of real estate property \| ft²	6.7
Virginia Tech
Organization and Basis of Presentation
Under-construction property value developed by Virginia Tech \| $	$ 1
JBG Smith, LP
Organization and Basis of Presentation
Ownership interest by parent	81.30%