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

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

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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

- Details

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

- 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:

Redeemable Noncontrolling Interests - Narrative (Details) - shares shares in Thousands		3 Months Ended	9 Months Ended
	Jul. 18, 2017	Sep. 30, 2018	Sep. 30, 2018
Noncontrolling Interest [Line Items]
Common Shares Issued During Period in Connection with Redemption of OP Units		2,962
JBG Smith, LP
Noncontrolling Interest [Line Items]
Ownership interest by parent		87.80%	87.80%
Consolidated Real Estate Venture
Noncontrolling Interest [Line Items]
Ownership interest by parent		85.40%	85.40%
Ownership interest by parent, threshold for capital contributions to cease		97.00%	97.00%
OP Units
Noncontrolling Interest [Line Items]
Common shares and OP Units issued in consideration	19,800		16,800
Common Shares Issued During Period in Connection with Redemption of OP Units		3,000
OP Units \| JBG Smith, LP
Noncontrolling Interest [Line Items]
Ownership interest by parent		12.20%	12.20%
Minimum
Noncontrolling Interest [Line Items]
Redemption period			2 years
Maximum
Noncontrolling Interest [Line Items]
Redemption period			7 years