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Intangible Assets (Textual) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Tenant Move-Outs Prior to End of the Lease Term [Member] |  |  |
Finite Lived Intangible Assets [Line Items] |  |  |
Intangible Assets Written Off Through Accelerated Amortization | $ 0.7 | $ 0.6 | $ 0.6

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- Definition Intangible assets written off through accelerated amortization. + References No definition available. + Details
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Namespace Prefix: | bdn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_LeaseArrangementTypeAxis=bdn_TenantMoveOutsPriorToEndOfLeaseTermMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |