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Segment Information Segment Information Textual (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
segment
Dec. 31, 2014
Segment Reporting Information [Line Items]    
Number of Reportable Segments 7us-gaap_NumberOfReportableSegments  
Investment in Real Estate Ventures, at equity $ 233,478us-gaap_EquityMethodInvestments $ 225,004us-gaap_EquityMethodInvestments
Coppell Associates [Member]    
Segment Reporting Information [Line Items]    
Investment in Real Estate Ventures, at equity $ (1,200)us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_CoppellAssociatesMember		 $ (1,200)us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_CoppellAssociatesMember
Durham, NC [Member]    
Segment Reporting Information [Line Items]    
Number of Real Estate Properties 1us-gaap_NumberOfRealEstateProperties
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= bdn_DurhamNCMember		  
1000 Atrium Way and Libertyview [Member]    
Segment Reporting Information [Line Items]    
Number of Real Estate Properties   2us-gaap_NumberOfRealEstateProperties
/ us-gaap_BusinessAcquisitionAxis
= bdn_A1000AtriumWayandLibertyviewMemberMember
New Jersey/ Delaware [Member]    
Segment Reporting Information [Line Items]    
Number of Real Estate Properties 5us-gaap_NumberOfRealEstateProperties
/ us-gaap_StatementGeographicalAxis
= bdn_NewJerseyDelawareMember		  
CALIFORNIA    
Segment Reporting Information [Line Items]    
Number of Real Estate Properties 1us-gaap_NumberOfRealEstateProperties
/ us-gaap_StatementGeographicalAxis
= stpr_CA