Name:	jbgs_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentBargainPurchaseReductionOfGain
Namespace Prefix:	jbgs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Number of Former Owners Turned Board Members

No definition available.

Name:	jbgs_NumberofFormerOwnersTurnedBoardMembers
Namespace Prefix:	jbgs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Number of Former Owners Turned Employees

No definition available.

Name:	jbgs_NumberofFormerOwnersTurnedEmployees
Namespace Prefix:	jbgs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Number of Unrelated Owners

No definition available.

Name:	jbgs_NumberofUnrelatedOwners
Namespace Prefix:	jbgs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Area of a real estate property.

No definition available.

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

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

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

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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

The number of real estate properties owned as of the balance sheet date.

No definition available.

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

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

No definition available.

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

Name:	us-gaap_BusinessAcquisitionAxis=jbgs_JBGCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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

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

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

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