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Limited Partners' Non-Controlling Interests in the Parent Company (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
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Noncontrolling Interest [Abstract] |  |
Aggregate amount related to non-controlling interests classified within equity | $ 9.4 | $ 10.1
Settlement value of non controlling interest in operating partnership | $ 14.9 | $ 12.6

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- Definition Minority interest in operating partnerships settlement value. + References No definition available. + Details
Name: | bdn_MinorityInterestInOperatingPartnershipsSettlementValue
Namespace Prefix: | bdn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Carrying amount of the equity interests owned by noncontrolling partners in an operating partnership included in the entity's consolidated financial statements. + References No definition available. + Details
Name: | us-gaap_MinorityInterestInOperatingPartnerships
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_NoncontrollingInterestAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration