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DEFERRED COSTS - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Deferred Costs (Textual) [Abstract] |  |  |
Capitalized internal direct leasing costs | $ 1.7 | $ 3.9 | $ 4.6

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- Definition Capitalized internal direct leasing costs. + References No definition available. + Details
Name: | bdn_CapitalizedInternalDirectLeasingCosts
Namespace Prefix: | bdn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Deferred costs textual. + References No definition available. + Details
Name: | bdn_DeferredCostsTextualAbstract
Namespace Prefix: | bdn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration