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INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Austin Venture (Details)
$ in Millions
Dec. 11, 2018
USD ($)
ft²
property
Dec. 31, 2020
ft²
property
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Oct. 16, 2013
USD ($)
ft²
property
Schedule of Equity Method Investments [Line Items]          
Number of properties | property   82      
Area of real estate property | ft²   13,852,464      
Brandywine Realty Trust          
Schedule of Equity Method Investments [Line Items]          
Ownership percentage   50.00%      
Equity method investment, additional distribution rights   10.00%      
Brandywine Realty Trust | Austin Joint Venture          
Schedule of Equity Method Investments [Line Items]          
Area of real estate property | ft²         1,398,826
Number of properties contributed to a joint venture | property         7
Aggregate gross sales price of a joint venture | $         $ 330.0
Equity method investment, agreement to pay future capital expenditures | $     $ 4.4 $ 0.8 $ 5.2
DRA Advisors LLC          
Schedule of Equity Method Investments [Line Items]          
Ownership percentage   50.00%      
DRA Austin Venture          
Schedule of Equity Method Investments [Line Items]          
Number of properties | property 12        
Area of real estate property | ft² 1,570,123        
Ownership percentage 50.00%        
Aggregate purchase price | $ $ 535.1