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INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - 4040 Wilson Venture (Details) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jul. 31, 2013 USD ($) a ft² property | Dec. 31, 2019 USD ($) ft² property | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items] |  |  |  |
Area of real estate property | ft² |  | 16,711,387 |  |
Number of Properties | property |  | 95 |  |
Cash paid to acquire real estate ventures |  | $ 2,181 | $ 0 | $ 0
Advanced under the construction loan |  | $ 253 | $ 908 | 6,638
4040 Wilson Venture |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Ownership percentage | 50.00% | 50.00% |  |
Area owned by real estate venture of undeveloped parcels of land | a | 1.3 |  |  |
Secured construction loan with total borrowing capacity |  |  |  | $ 150,000
Advanced under the construction loan |  | $ 114,800 |  |
Mixed Use Property | 4040 Wilson Venture |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Area of real estate property | ft² | 427,500 |  |  |
Number of Properties | property | 8 |  |  |
Brandywine Realty Trust |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Ownership percentage |  | 50.00% |  |
Brandywine Realty Trust | 4040 Wilson Venture |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Cash paid to acquire real estate ventures | $ 36,000 |  |  |

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