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

No definition available.

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

- Definition

Noncontrolling Interest, Capital Contribution Threshold, Ownership Percentage by Parent

+ References

No definition available.

+ Details

Name:	jbgs_NoncontrollingInterestCapitalContributionThresholdOwnershipPercentagebyParent
Namespace Prefix:	jbgs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of units in service.

+ References

No definition available.

+ Details

Name:	jbgs_PercentageOfUnitsInService
Namespace Prefix:	jbgs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Redeemable Noncontrolling Interest, Redemption Period

+ References

No definition available.

+ Details

Name:	jbgs_RedeemableNoncontrollingInterestRedemptionPeriod
Namespace Prefix:	jbgs_
Data Type:	xbrli:durationItemType
Balance Type:	na
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:	num: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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

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

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
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:

Redeemable Noncontrolling Interests - Narrative (Details) - shares	1 Months Ended	6 Months Ended
	Jul. 31, 2020	Jun. 30, 2020	Jun. 30, 2019
Consolidated Real Estate Venture
Noncontrolling Interest [Line Items]
Ownership interest by parent, threshold for capital contributions to cease		97.00%
Percentage of units in service		40.00%
OP Units
Noncontrolling Interest [Line Items]
Conversion of common limited partnership units to common shares	81,069	942,940	1,700,000
Units outstanding		14,200,000
Minimum \| Consolidated Real Estate Venture
Noncontrolling Interest [Line Items]
Redemption period		2 years
Maximum \| Consolidated Real Estate Venture
Noncontrolling Interest [Line Items]
Redemption period		7 years
JBG Smith, LP
Noncontrolling Interest [Line Items]
Ownership interest by parent		90.40%
JBG Smith, LP \| OP Units
Noncontrolling Interest [Line Items]
Ownership interest by parent		9.60%
Consolidated Real Estate Venture
Noncontrolling Interest [Line Items]
Ownership interest by parent		95.70%