Variable Interest Entities (Details) $ in Thousands		1 Months Ended
	Sep. 30, 2021 USD ($) item	Mar. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($)
Variable Interest Entity [Line Items]
Assets	$ 6,008,978		$ 6,079,547
Liabilities	$ 2,378,289		2,342,593
Multifamily
Variable Interest Entity [Line Items]
Number of Units in Real Estate Property | item	7,776
JBG Smith, LP
Variable Interest Entity [Line Items]
Ownership interest by parent	90.80%
Unconsolidated VIE
Variable Interest Entity [Line Items]
Assets	$ 165,400		$ 116,200
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	29,700
Liabilities	4,500
Ground lessee equity funding	17,500
Ground lessee project funding through a mezzanine loan	11,700
Variable Interest Entity, Primary Beneficiary | Mortgages Payable
Variable Interest Entity [Line Items]
Principal amount		$ 227,000
Proceeds from issuance of mortgage loan	$ 0
Variable Interest Entity, Primary Beneficiary | Mortgages Payable | London Interbank Offered Rate (LIBOR)
Variable Interest Entity [Line Items]
Debt Instrument basis spread on variable rate		3.00%
Variable Interest Entity, Primary Beneficiary | 1900 Crystal Drive | Multifamily
Variable Interest Entity [Line Items]
Number of Units in Real Estate Property | item		808
Number of Towers in Real Estate Property | item		2