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Fair Value of Financial Instruments (Details Textuals) (USD $) In Millions | Jun. 30, 2011
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Fair Value of Financial Instruments (Textuals) [Abstract] |
Gross deferred gain on sale of properties | $ 12.9

X
- Definition Fair Value of Financial Instruments. + Details
Name: | bdn_FairValueOfFinancialInstrumentsTextualsAbstract
Namespace Prefix: | bdn
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of gain on the sale of property that does not qualify for gain recognition as of the balance sheet date. + Details
Name: | us-gaap_DeferredGainOnSaleOfProperty
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant