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Summary of Significant Accounting Policies Impairment or DIsposal of Long-Lived Assets (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Significant Acquisitions and Disposals [Line Items]      
Provision for impairment on assets held for sale $ 1,765us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf $ 0us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf $ 0us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf
Gains (Losses) on Sales of Investment Real Estate 4,901us-gaap_GainsLossesOnSalesOfInvestmentRealEstate 0us-gaap_GainsLossesOnSalesOfInvestmentRealEstate 0us-gaap_GainsLossesOnSalesOfInvestmentRealEstate
Valleybrooke Office Park [Member]      
Significant Acquisitions and Disposals [Line Items]      
Provision for impairment on assets held for sale 1,765us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= bdn_ValleybrookeOfficeParkMember		    
Gains (Losses) on Sales of Investment Real Estate $ 200us-gaap_GainsLossesOnSalesOfInvestmentRealEstate
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= bdn_ValleybrookeOfficeParkMember