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Fair Value of Financial Instruments (Details Textuals) (USD $) In Millions	Jun. 30, 2011
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

X

- 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