Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($)
Summary of Significant Accounting Policies
Lease deferral requests granted - COVID	$ 1.9

Amount of lease deferral requests granted during the period due to unusual event.

No definition available.

Name:	jbgs_LeaseDeferralRequestsDueToUnusualEvent
Namespace Prefix:	jbgs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration