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Investment in Unconsolidated Ventures (Narrative) (Details) (USD $)
 3 Months Ended 0 Months Ended
Mar. 31, 2015
apartment_unit
Room
sqft
acre
real_estate_venture
building
Jan. 30, 2015
Feb. 27, 2015
Dec. 31, 2014
Mar. 31, 2014
real_estate_venture
Dec. 19, 2007
sqft
Schedule of Equity Method Investments [Line Items]            
Number of unconsolidated investments in Real Estate Ventures 17bdn_NumberOfUnconsolidatedInvestmentsInRealEstateVentures       17bdn_NumberOfUnconsolidatedInvestmentsInRealEstateVentures  
Equity Method Investments including net liabilities $ 232,300,000bdn_EquityMethodInvestmentsincludingnetliabilities          
Company's share of equity (Company's basis) 233,478,000us-gaap_EquityMethodInvestments     225,004,000us-gaap_EquityMethodInvestments    
Number of negative investment real estate ventures 1bdn_NumberofRealEstateVentureswithNegativeInvestmentBalances          
Number of real estate ventures that owns buildings 11bdn_NumberOfRealEstateVenturesThatOwnsBuildings          
Number of office buildings in Real Estate Ventures 65bdn_NumberOfOfficeBuildingsInRealEstateVentures          
Aggregate Approximate Area Of Office Buildings 6,700,000bdn_AggregateApproximateAreaOfOfficeBuildings          
Number of real estate ventures that owns undeveloped land 1bdn_NumberOfRealEstateVenturesThatOwnsUndevelopedLand          
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land 3bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand          
Number of real estate ventures that owns land under development 3bdn_NumberOfRealEstateVenturesThatOwnsLandUnderDevelopment          
Area Owned By Real Estate Venture in Parcels Of Land Under Development 22.6bdn_AreaOwnedByRealEstateVentureInParcelsOfLandUnderDevelopment          
Number of Real Estate Investments in residential towers 1bdn_NumberofRealEstateInvestmentsinresidentialtowers          
Number of apartment units in a Real Estate Venture 345bdn_NumberofapartmentunitsinaRealEstateVenture          
Number of real estate ventures developed hotel property 1bdn_NumberOfRealEstateVenturesDevelopedHotelProperty          
Number Of Rooms Contain In One Real Estate Venture Developed As Hotel Property 137bdn_NumberOfRoomsContainInOneRealEstateVentureDevelopedAsHotelProperty          
Minimum Percentage Of Unconsolidated Equity Method Investment Ownership 20.00%bdn_MinimumPercentageOfUnconsolidatedEquityMethodInvestmentOwnership          
Maximum Percentage Of Unconsolidated Equity Method Investment Ownership 65.00%bdn_MaximumPercentageOfUnconsolidatedEquityMethodInvestmentOwnership          
River Place [Member]            
Schedule of Equity Method Investments [Line Items]            
Proceeds from Collection of Notes Receivable   88,000,000us-gaap_ProceedsFromCollectionOfNotesReceivable
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_RiverPlaceMember		        
Coppell Associates [Member]            
Schedule of Equity Method Investments [Line Items]            
Company's share of equity (Company's basis) (1,200,000)us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_CoppellAssociatesMember		     (1,200,000)us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_CoppellAssociatesMember		    
GI Interchange Office LLC (DRA — N. PA) [Member]            
Schedule of Equity Method Investments [Line Items]            
Number of Real Estate Properties           29us-gaap_NumberOfRealEstateProperties
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_GiInterchangeOfficeLlcDraNPaMember
Net Rentable Area           1,611,961us-gaap_NetRentableArea
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_GiInterchangeOfficeLlcDraNPaMember
Forbearance Agreement, Lender Extension Term     60 days      
Non-Recourse Debt     174,200,000us-gaap_NonRecourseDebt
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_GiInterchangeOfficeLlcDraNPaMember		      
TB-BDN Plymouth Apartments [Member]            
Schedule of Equity Method Investments [Line Items]            
Guarantor Obligations, Current Carrying Value 3,200,000us-gaap_GuarantyLiabilities
/ dei_LegalEntityAxis
= bdn_TbBdnPlymouthApartmentsMember		          
Unconsolidated Real Estate Ventures [Member]            
Schedule of Equity Method Investments [Line Items]            
Net rentable square feet 6,700,000us-gaap_AreaOfRealEstateProperty
/ dei_LegalEntityAxis
= us-gaap_CorporateJointVentureMember		       5,700,000us-gaap_AreaOfRealEstateProperty
/ dei_LegalEntityAxis
= us-gaap_CorporateJointVentureMember		  
The Grove at Cira Centre South [Member]            
Schedule of Equity Method Investments [Line Items]            
Guarantor Obligations, Current Carrying Value 24,700,000us-gaap_GuarantyLiabilities
/ dei_LegalEntityAxis
= bdn_GroveAtCiraCentreSouthMember		          
PJP VII [Member]            
Schedule of Equity Method Investments [Line Items]            
Guarantor Obligations, Current Carrying Value $ 500,000us-gaap_GuarantyLiabilities
/ dei_LegalEntityAxis
= bdn_PjpViiMember		          
DRA Advisors LLC [Member] | GI Interchange Office LLC (DRA — N. PA) [Member]            
Schedule of Equity Method Investments [Line Items]            
Equity Method Investment, Ownership Percentage           80.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ bdn_JointVentureMembersAxis
= bdn_DRAAdvisorsLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_GiInterchangeOfficeLlcDraNPaMember
Brandywine Realty Trust [Member] | GI Interchange Office LLC (DRA — N. PA) [Member]            
Schedule of Equity Method Investments [Line Items]            
Equity Method Investment, Ownership Percentage           20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ bdn_JointVentureMembersAxis
= bdn_BrandywineRealtyTrustMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bdn_GiInterchangeOfficeLlcDraNPaMember