INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - JGB Ventures (Details) - a	Dec. 31, 2019	May 29, 2015
JBG 1250 First Street Office
Schedule of Equity Method Investments [Line Items]
Ownership percentage	70.00%	70.00%
Area owned by real estate venture of undeveloped parcels of land		0.5
JBG 51 N 50 Patterson
Schedule of Equity Method Investments [Line Items]
Ownership percentage	70.00%
Area owned by real estate venture of undeveloped parcels of land		0.9
JBG Ventures | JBG 1250 First Street Office
Schedule of Equity Method Investments [Line Items]
Ownership percentage		30.00%