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Debt Obligations (Consolidated Debt Obligations Outstanding) (Details) (USD $)
 0 Months Ended 12 Months Ended
Sep. 16, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount   $ 376,174,000us-gaap_ExtinguishmentOfDebtAmount $ 29,250,000us-gaap_ExtinguishmentOfDebtAmount $ 164,968,000us-gaap_ExtinguishmentOfDebtAmount
Early Repayment of Senior Debt   383,768,000us-gaap_EarlyRepaymentOfSeniorDebt 31,369,000us-gaap_EarlyRepaymentOfSeniorDebt 338,097,000us-gaap_EarlyRepaymentOfSeniorDebt
Gain (Loss) on Early Extinguishment of Debt   (7,594,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost (2,119,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost (22,002,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
Write off of Deferred Debt Issuance Cost   152,000us-gaap_WriteOffOfDeferredDebtIssuanceCost 40,000us-gaap_WriteOffOfDeferredDebtIssuanceCost 451,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
Gains (Losses) on Extinguishment of Debt 2,606,000us-gaap_GainsLossesOnExtinguishmentOfDebt 7,594,000us-gaap_GainsLossesOnExtinguishmentOfDebt 2,119,000us-gaap_GainsLossesOnExtinguishmentOfDebt 22,002,000us-gaap_GainsLossesOnExtinguishmentOfDebt
Consolidated debt obligations        
Plus: premiums/(discounts), net   (8,155,000)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet    
Total mortgage indebtedness   654,590,000us-gaap_SecuredDebt 670,151,000us-gaap_SecuredDebt  
Total Debt Obligations   2,451,308,000us-gaap_LongTermDebt 2,595,381,000us-gaap_LongTermDebt  
Repayments of Unsecured Debt   250,828,000us-gaap_RepaymentsOfUnsecuredDebt 0us-gaap_RepaymentsOfUnsecuredDebt 190,485,000us-gaap_RepaymentsOfUnsecuredDebt
Long Term Debt Maturities Repayments Of Principal   2,459,463,000bdn_LongTermDebtMaturitiesRepaymentsOfPrincipal    
Recognized hedge activity 800,000us-gaap_DerivativeGainLossOnDerivativeNet 828,000us-gaap_DerivativeGainLossOnDerivativeNet 0us-gaap_DerivativeGainLossOnDerivativeNet 2,985,000us-gaap_DerivativeGainLossOnDerivativeNet
Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   655,934,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 669,762,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		  
Plus: premiums/(discounts), net   (1,344,000)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 389,000us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		  
Total mortgage indebtedness   654,590,000us-gaap_SecuredDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 670,151,000us-gaap_SecuredDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		  
Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   1,803,529,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 1,929,703,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Plus: premiums/(discounts), net   (6,811,000)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 (4,473,000)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Total unsecured indebtedness   1,796,718,000bdn_UnsecuredIndebtedness
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 1,925,230,000bdn_UnsecuredIndebtedness
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Note Five [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount 42,700,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Gains (Losses) on Extinguishment of Debt   5,000,000us-gaap_GainsLossesOnExtinguishmentOfDebt
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Consolidated debt obligations        
Long-term Debt, Gross   0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 157,625,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   May 15, 2015    
Effective interest rate   7.76%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Repurchased Face Amount 114,900,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFiveMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt Instrument, Redemption, Description $1,070.24 per $1,000      
New Revolving Credit Facility [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Line of Credit Facility, Maximum Borrowing Capacity   600,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Consolidated debt obligations        
Debt instrument, basis spread on variable rate   1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Three-Year Term Loan - Swapped to fixed [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_ThreeYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 150,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_ThreeYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Feb. 01, 2015    
Effective interest rate   2.60%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_ThreeYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Repurchased Face Amount 150,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_ThreeYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Four-Year Term Loan - Swapped to fixed [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Debt Instrument, Repurchased Face Amount 100,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_FourYearTermLoanSwappedToFixedMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Three and Four Year Term Loan [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Write off of Deferred Debt Issuance Cost 300,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_DebtInstrumentAxis
= bdn_ThreeAndFourYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Four-Year Term Loan - Variable [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_FourYearTermLoanVariableMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 100,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_FourYearTermLoanVariableMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Feb. 01, 2016    
Debt Instrument, Interest Rate Terms   LIBOR + 1.75%    
Seven Year Term Loan - Swapped to fixed [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   200,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_SevenYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 200,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_SevenYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Feb. 01, 2019    
Effective interest rate   3.62%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_SevenYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Term   7 years    
Debt Instrument, Face Amount   200,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_SevenYearTermLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Line of Credit and Seven Year Term Loan [Member]        
Consolidated debt obligations        
Debt Instrument, Interest Rate Terms   Based on the Company's current credit rating, the spread will be 150 basis points under the Credit Facility and 190 basis points under the seven-year term loan    
Debt Instrument, Interest Rate Terms   federal funds rate plus 0.50%    
$300.0M 5.750% Guaranteed Notes due 2012 [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Debt Instrument, Interest Rate, Stated Percentage   5.75%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
$250.0M 5.400% Guaranteed Notes due 2014 [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount 75,100,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Consolidated debt obligations        
Long-term Debt, Gross   0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 218,549,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Nov. 01, 2014    
Effective interest rate   5.53%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   5.40%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Repurchased Face Amount 143,500,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt Instrument, Redemption, Description $1,026.88 per $1,000      
$250.0M 6.000% Guaranteed Notes due 2016 [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   149,919,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSixMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 149,919,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSixMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Apr. 01, 2016    
Effective interest rate   5.95%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSixMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   6.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSixMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSixMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
$300.0M 5.700% Guaranteed Notes due 2017 [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   300,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSevenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 300,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSevenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   May 01, 2017    
Effective interest rate   5.68%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSevenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   5.70%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSevenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   300,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteSevenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
$325.0M 4.950% Guaranteed Notes due 2018 [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   325,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteEightMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 325,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteEightMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Apr. 15, 2018    
Effective interest rate   5.13%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteEightMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   4.95%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_NoteEightMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   325,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_NoteEightMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Note 2023 [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   250,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2023Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 250,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2023Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Feb. 15, 2023    
Effective interest rate   4.02%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2023Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   3.95%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2023Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2023Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Note 2024 [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Debt instrument, Unamortized discount, Percent of face amount 99.388%bdn_DebtinstrumentUnamortizeddiscountPercentoffaceamount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt instrument, Yield to maturity 4.175%bdn_DebtinstrumentYieldtomaturity
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt instrument, Yield to maturity spread at time of pricing 1.70%bdn_DebtinstrumentYieldtomaturityspreadattimeofpricing
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt Instrument, Unamortized Discount   1,500,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Consolidated debt obligations        
Long-term Debt, Gross   250,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Oct. 01, 2024    
Effective interest rate   4.23%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   4.10%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2024Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Note 2029 [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Debt instrument, Unamortized discount, Percent of face amount 99.191%bdn_DebtinstrumentUnamortizeddiscountPercentoffaceamount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt instrument, Yield to maturity 4.625%bdn_DebtinstrumentYieldtomaturity
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt instrument, Yield to maturity spread at time of pricing 2.15%bdn_DebtinstrumentYieldtomaturityspreadattimeofpricing
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Debt Instrument, Unamortized Discount   2,000,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Consolidated debt obligations        
Long-term Debt, Gross   250,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 0us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Oct. 01, 2029    
Effective interest rate   4.60%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Interest Rate, Stated Percentage   4.55%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Debt Instrument, Face Amount   250,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bdn_Note2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Notes 2024 and 2029 [Member] | Unsecured Debt [Member]        
Participating Mortgage Loans [Line Items]        
Proceeds from Notes Payable 492,900,000us-gaap_ProceedsFromNotesPayable
/ us-gaap_DebtInstrumentAxis
= bdn_Notes2024and2029Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		      
Indenture IA (Preferred Trust I) [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   27,062,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIaPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 27,062,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIaPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Mar. 30, 2035    
Effective interest rate   2.75%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIaPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Indenture IB (Preferred Trust I) [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   25,774,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIbPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 25,774,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIbPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Apr. 30, 2035    
Effective interest rate   3.30%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIbPreferredTrustIMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Indenture II (Preferred Trust II) [Member] | Unsecured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   25,774,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIiPreferredTrustIiMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 25,774,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIiPreferredTrustIiMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		  
Debt Instrument, Maturity Date   Jul. 30, 2035    
Effective interest rate   3.09%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= bdn_IndentureIiPreferredTrustIiMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Tysons Corner [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   89,513,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TysonsCornerMember		 91,395,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TysonsCornerMember		  
Debt Instrument, Maturity Date   Aug. 01, 2015    
Effective interest rate   5.36%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TysonsCornerMember		    
One Commerce Square [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   123,205,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_OneCommerceSquareMember		 125,089,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_OneCommerceSquareMember		  
Debt Instrument, Maturity Date   Jan. 06, 2016    
Effective interest rate   3.68%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_OneCommerceSquareMember		    
Two Logan Square [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   87,767,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoLoganSquareMember		 88,583,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoLoganSquareMember		  
Debt Instrument, Maturity Date   Apr. 01, 2016    
Effective interest rate   7.57%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoLoganSquareMember		    
Fairview Eleven Tower [Member]        
Participating Mortgage Loans [Line Items]        
Equity Method Investment, Ownership Percentage   50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ bdn_PropertyLocationAxis
= bdn_FairviewElevenTowerMember		    
Fairview Eleven Tower [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   21,242,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_FairviewElevenTowerMember		 21,630,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_FairviewElevenTowerMember		  
Debt Instrument, Maturity Date   Jan. 01, 2017    
Effective interest rate   4.25%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_FairviewElevenTowerMember		    
Two Commerce Square [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   112,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoCommerceSquareMember		 112,000,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoCommerceSquareMember		  
Debt Instrument, Maturity Date   Apr. 05, 2023    
Effective interest rate   4.51%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_TwoCommerceSquareMember		    
IRS Philadelphia Campus [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   184,442,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_IrsPhiladelphiaCampusMember		 190,964,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_IrsPhiladelphiaCampusMember		  
Debt Instrument, Maturity Date   Sep. 10, 2030    
Effective interest rate   7.00%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_IrsPhiladelphiaCampusMember		    
Cira South Garage [Member] | Secured Debt [Member]        
Consolidated debt obligations        
Long-term Debt, Gross   37,765,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_CiraSouthGarageMember		 40,101,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_CiraSouthGarageMember		  
Debt Instrument, Maturity Date   Sep. 10, 2030    
Effective interest rate   7.12%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
/ bdn_PropertyLocationAxis
= bdn_CiraSouthGarageMember		    
Note Four [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount   218,549,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 19,830,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 4,302,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember
Early Repayment of Senior Debt   219,404,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 20,853,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 4,566,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember
Gain (Loss) on Early Extinguishment of Debt   (855,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 (1,020,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 (264,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember
Write off of Deferred Debt Issuance Cost   9,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 16,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember		 8,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFourMember
Note Three [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount       301,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteThreeMember
Early Repayment of Senior Debt       303,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteThreeMember
Gain (Loss) on Early Extinguishment of Debt       (2,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteThreeMember
Write off of Deferred Debt Issuance Cost       0us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteThreeMember
Note Five [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount   157,625,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 8,910,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 60,794,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember
Early Repayment of Senior Debt   164,364,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 9,945,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 69,497,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember
Gain (Loss) on Early Extinguishment of Debt   (6,739,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 (1,036,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 (8,712,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember
Write off of Deferred Debt Issuance Cost   143,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 23,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember		 183,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteFiveMember
Note Six [Member]        
Participating Mortgage Loans [Line Items]        
Extinguishment of Debt, Amount     510,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember		 99,571,000us-gaap_ExtinguishmentOfDebtAmount
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember
Early Repayment of Senior Debt     571,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember		 112,541,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember
Gain (Loss) on Early Extinguishment of Debt     (63,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember		 (13,024,000)us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember
Write off of Deferred Debt Issuance Cost     1,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember		 260,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_ExtinguishmentOfDebtAxis
= bdn_NoteSixMember
Discharge of Debt [Member]        
Participating Mortgage Loans [Line Items]        
Early Repayment of Senior Debt   $ 383,768,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= us-gaap_DischargeOfDebtMember		 $ 31,369,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= us-gaap_DischargeOfDebtMember		 $ 186,907,000us-gaap_EarlyRepaymentOfSeniorDebt
/ us-gaap_ExtinguishmentOfDebtAxis
= us-gaap_DischargeOfDebtMember