Common Shares Issued During Period in Connection with Redemption of OP Units.

No definition available.

Name:	jbgs_CommonSharesIssuedDuringPeriodsInConnectionWithRedemptionOfOpUnits
Namespace Prefix:	jbgs_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of ownership interest held in the real estate property.

+ References

No definition available.

+ Details

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

- Definition

Percentage of ownership interest in assets sold.

+ References

No definition available.

+ Details

Name:	jbgs_PercentageOfOwnershipInterestInAssetsSold
Namespace Prefix:	jbgs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash inflow on sale of interest in consolidated real estate venture, classified as financing activities.

+ References

No definition available.

+ Details

Name:	jbgs_ProceedsFromSaleOfInterestInConsolidatedRealEstateVentureClassifiedAsFinancingActivities
Namespace Prefix:	jbgs_
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_MinorityInterestLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

The number of units or equivalent units outstanding for all classes.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-5

+ Details

Name:	us-gaap_UnitsOfPartnershipInterestAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_StatementClassOfStockAxis=jbgs_OPUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=jbgs_JBGSmithLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=jbgs_ConsolidatedRealEstateVentureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=jbgs_WestHalfMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Redeemable Noncontrolling Interests - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended
	Oct. 24, 2025	May 31, 2025	Sep. 30, 2025	Sep. 30, 2024
Redeemable Noncontrolling Interests
Proceeds from the sale of interest in consolidated real estate venture			$ 100,000
OP Units
Redeemable Noncontrolling Interests
Redemption of common limited partnership units to common shares			1,200,000	827,012
Subsequent Event \| OP Units
Redeemable Noncontrolling Interests
Redemption of common limited partnership units to common shares	262,641
JBG Smith, LP
Redeemable Noncontrolling Interests
Ownership interest by parent			81.30%
JBG Smith, LP \| OP Units
Redeemable Noncontrolling Interests
Units outstanding			13,600,000
Ownership interest by parent			18.70%
Consolidated Real Estate Venture \| West Half
Redeemable Noncontrolling Interests
Percentage of ownership interest in assets sold		40.00%
Proceeds from the sale of interest in consolidated real estate venture		$ 100,000
Percentage of ownership interest held in real estate property		60.00%