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Deferred Costs (Textual) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Deferred Costs (Textual) [Abstract] |  |  |
Capitalized internal direct leasing costs | $ 3.9 | $ 4.6 | $ 5.0

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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