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Transactions with Vornado and Related Parties (Details)			1 Months Ended		12 Months Ended
Transactions with Vornado and Related Parties (Details)	Jul. 18, 2017 USD ($)	Jul. 17, 2017 USD ($)	Jun. 30, 2016 USD ($) ft²	Aug. 31, 2014 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Borrowings under revolving credit facility					$ 200,000,000	$ 35,000,000	$ 115,751,000
Qualified Affordable Housing Project Investments, Total Capital Commitments					104,800,000
Corporate and other					46,822,000	33,728,000	39,350,000
Affiliated Entity [Member] \| Washington Housing Initiative [Member]
Related Party Transaction [Line Items]
Qualified Affordable Housing Project Investments, Commitment					10,200,000
Affiliated Entity [Member] \| Legacy JBG Funds [Member]
Related Party Transaction [Line Items]
Corporate and other					5,000,000.0	4,900,000	2,200,000
Affiliated Entity [Member] \| Separation and Combination transaction \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Expenses from related parties					3,600,000	2,200,000
Revenue from related parties					2,000,000.0	2,100,000	779,000
Affiliated Entity [Member] \| Supervisory Services of Properties [Member] \| BMS
Related Party Transaction [Line Items]
Related party transaction amount					21,800,000	20,900,000	13,600,000
Affiliated Entity [Member] \| Allocations of Centralized Corporate Costs [Member] \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party							13,000,000.0
Affiliated Entity [Member] \| Fees from Legacy JBG Funds and Washington Housing Initiative [Member] \| Legacy JBG Funds and Washington Housing Initiative [Member]
Related Party Transaction [Line Items]
Third-party real estate services, including reimbursements					36,500,000
Accounts Receivable, Related Parties					$ 6,200,000
Affiliated Entity [Member] \| Fees from Legacy JBG Funds \| Legacy JBG Funds [Member]
Related Party Transaction [Line Items]
Third-party real estate services, including reimbursements						33,800,000	19,900,000
Accounts Receivable, Related Parties						$ 3,600,000
Director [Member] \| Consulting Agreement [Member]
Related Party Transaction [Line Items]
Expenses from related parties							16,400,000
Related Party Transaction, Monthly Transaction Amount		$ 169,400
Related Party Transaction, Initial Potential Service Period		24 years
Note Agreement for Development of The Bartlett [Member] \| Affiliated Entity [Member] \| Financing Transactions [Member] \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Debt Instrument, Face Amount	$ 170,000,000.0
Interest Expense, Related Party							4,100,000
Financing of the Universal Buildings [Member]
Related Party Transaction [Line Items]
Debt Instrument, Face Amount				$ 185,000,000.0
Financing of the Universal Buildings [Member] \| Affiliated Entity [Member] \| Financing Transactions [Member] \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Origination of Notes Receivable from Related Parties				$ 86,000,000.0
Interest Income, Related Party							1,800,000
Mortgage loan secured by Bowen Building [Member] \| Affiliated Entity [Member] \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Interest Expense, Related Party							$ 1,300,000
Repayments of Secured Debt			$ 115,000,000.0
Debt Instrument, Increase, Accrued Interest			608,000
Borrowings under revolving credit facility			$ 115,600,000
Universal Buildings, Washington DC [Member]
Related Party Transaction [Line Items]
Area of real estate property (in square feet) \| ft²			231,000	687,000
London Interbank Offered Rate (LIBOR) [Member] \| Financing of the Universal Buildings [Member] \| Affiliated Entity [Member] \| Financing Transactions [Member] \| Vornado Realty Trust [Member]
Related Party Transaction [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.90%
JBG Companies [Member]
Related Party Transaction [Line Items]
Business Combination, Consideration Transferred, Liabilities Incurred	$ 4,100,000