The amount of consideration for the future asset acquisition.

No definition available.

Name:	jbgs_AssetAcquisitionConsiderationToBeTransferred
Namespace Prefix:	jbgs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Gain (loss) from cash and land contribution to a real estate venture.

+ References

No definition available.

+ Details

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

- Definition

Number of real estate units to be acquired.

+ References

No definition available.

+ Details

Name:	jbgs_NumberOfRealEstateUnitsToBeAcquired
Namespace Prefix:	jbgs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of real estate ventures in which the entity invested cash in and contributed one parcel of land to during the period.

+ References

No definition available.

+ Details

Name:	jbgs_NumberOfRealEstateVenturesInWhichCashInvestedAndLandContributed
Namespace Prefix:	jbgs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of occupancy in the multifamily portion of the building.

+ References

No definition available.

+ Details

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

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jbgs_J.p.MorganGlobalAlternativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jbgs_AssetAcquisitionAxis=jbgs_BatleyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisition, Dispositions and Assets Held for Sale - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Apr. 30, 2021 USD ($) property	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Schedule of Equity Method Investments [Line Items]
Income (loss) from unconsolidated real estate ventures, net			$ 20,503	$ (965)	$ 23,513	$ (17,142)
Landmark and CBREI
Schedule of Equity Method Investments [Line Items]
Income (loss) from unconsolidated real estate ventures, net					28,326
Potomac Yard Mixed Use Development \| J.P. Morgan Global Alternatives ("J.P. Morgan")
Schedule of Equity Method Investments [Line Items]
Number of real estate ventures in which cash was invested and land contributed \| property		2
Gain from contribution to real estate ventures		$ 11,300
The Batley
Schedule of Equity Method Investments [Line Items]
Number of real estate units to be acquired	432
Purchase price	$ 205,000		$ 205,000		$ 205,000
Percentage of occupancy in the multifamily portion of the building	90.70%