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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
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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 |  |  |  |

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