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Fair Value of Financial Instruments (Details Textuals) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2012 Properties
Fair Value of Financial Instruments (Textuals) [Abstract] |
Gross deferred gain on sale of properties | $ 12.9
Number of properties sold (in properties) | 2

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- Details
Name: | bdn_FairValueOfFinancialInstrumentsTextualsAbstract
Namespace Prefix: | bdn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of properties sold. + References No definition available. + Details
Name: | bdn_NumberOfPropertiesSold
Namespace Prefix: | bdn_
Data Type: | xbrli:integerItemType
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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 40 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.U.Q2) -URI http://asc.fasb.org/extlink&oid=6955272&loc=d3e221323-122791 + Details
Name: | us-gaap_DeferredGainOnSaleOfProperty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant