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Investment in Unconsolidated Ventures (Narrative) (Details) (USD $) | 12 Months Ended | 0 Months Ended |  |  |  |  |  |
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Dec. 31, 2014 sqft Buildings Real_Estate_Ventures Room acre ApartmentUnits | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Oct. 17, 2014 | Jul. 31, 2014 | Jul. 31, 2013 acre sqft | Jun. 19, 2013 | Oct. 16, 2013 | Apr. 03, 2014 | Jan. 20, 2011 acre | Mar. 26, 2013 | Jan. 25, 2013 beds Storey acre | Oct. 20, 2014 | Oct. 21, 2014 | Dec. 19, 2013 Storey
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of apartment units in a Real Estate Venture | 345 bdn_NumberofapartmentunitsinaRealEstateVenture |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain (loss) on real estate venture transactions | $ (417,000)bdn_NetGainLossOnRealEstateVentureTransactions | $ 29,604,000 bdn_NetGainLossOnRealEstateVentureTransactions | $ (950,000)bdn_NetGainLossOnRealEstateVentureTransactions |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from the contribution of land to an unconsolidated real estate venture | 8,212,000 bdn_Netproceedsfromthecontributionoflandtoanunconsolidatedrealestateventure | 0 bdn_Netproceedsfromthecontributionoflandtoanunconsolidatedrealestateventure | 0 bdn_Netproceedsfromthecontributionoflandtoanunconsolidatedrealestateventure |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments | 46,098,000 us-gaap_PaymentsToAcquireEquityMethodInvestments | 33,069,000 us-gaap_PaymentsToAcquireEquityMethodInvestments | 65,354,000 us-gaap_PaymentsToAcquireEquityMethodInvestments |  |  |  |  |  |  |  |  |  |  |  |  |
Company's share of equity (Company's basis) | 225,004,000 us-gaap_EquityMethodInvestments | 180,512,000 us-gaap_EquityMethodInvestments | 193,555,000 us-gaap_EquityMethodInvestments |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain on real estate venture transactions | (417,000)us-gaap_NonmonetaryTransactionGainLossRecognizedOnTransfer | 3,683,000 us-gaap_NonmonetaryTransactionGainLossRecognizedOnTransfer | 0 us-gaap_NonmonetaryTransactionGainLossRecognizedOnTransfer |  |  |  |  |  |  |  |  |  |  |  |  |
Number of unconsolidated Real Estate Ventures | 17 bdn_NumberOfUnconsolidatedInvestmentsInRealEstateVentures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investments including net liabilities | 223,790,000 bdn_EquityMethodInvestmentsincludingnetliabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate ventures that owns 51 office buildings | 11 bdn_NumberOfRealEstateVenturesThatOwnsBuildings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of office buildings owned by 15 Real Estate Ventures | 65 bdn_NumberOfOfficeBuildingsInRealEstateVentures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net rentable square feet of 51 office buildings owned the 15 Real Estate Ventures | 6,700,000 bdn_AggregateApproximateAreaOfOfficeBuildings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate ventures that owns undeveloped land | 1 bdn_NumberOfRealEstateVenturesThatOwnsUndevelopedLand |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of undeveloped parcels of land (in acres) owned by a Real Estate Venture | 3.0 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate ventures that owns land under development | 4 bdn_NumberOfRealEstateVenturesThatOwnsLandUnderDevelopment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area Owned By Real Estate Venture in Parcels Of Land Under Development | 22.6 bdn_AreaOwnedByRealEstateVentureInParcelsOfLandUnderDevelopment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate ventures developed hotel property | 1 bdn_NumberOfRealEstateVenturesDevelopedHotelProperty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of rooms in a hotel property developed by one Real Estate Venture | 137 bdn_NumberOfRoomsContainInOneRealEstateVentureDevelopedAsHotelProperty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum ownership interest in unconsolidated Real Estate Ventures | 20.00%bdn_MinimumPercentageOfUnconsolidatedEquityMethodInvestmentOwnership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum ownership interest in unconsolidated Real Estate Ventures | 65.00%bdn_MaximumPercentageOfUnconsolidatedEquityMethodInvestmentOwnership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain (loss) on sale of undepreciated real estate | 458,000 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain | 6,866,000 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain | 0 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain |  |  |  |  |  |  |  |  |  |  |  |  |
Brandywine Nineteen Nineteen Ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |  |  | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |
Company's share of equity (Company's basis) | 12,823,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of undeveloped parcels of land (in acres) owned by a Real Estate Venture |  |  |  |  |  |  |  |  |  |  | 1 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |
Payments to Acquire Land |  |  |  | 9,300,000 us-gaap_PaymentsToAcquireLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |  |  |  |  |
Austin, Texas [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors of a building |  |  |  |  |  | 3 bdn_NumberOfFloorsOfBuilding / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinTexasMember |  |  |  |  |  |  |  |  |  |
BDN Beacon Venture LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  | 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BdnBeaconVentureLlcMember |  |  |  |
Company's share of equity (Company's basis) |  |  |  |  |  |  |  |  |  |  |  | 17,000,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BdnBeaconVentureLlcMember |  |  |  |
Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment, Consideration transferred |  |  |  |  | 128,100,000 bdn_EquitymethodinvestmentConsiderationtransferred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember | 48,200,000 bdn_EquitymethodinvestmentConsiderationtransferred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |
Short-term Bank Loans and Notes Payable | 88,000,000 us-gaap_ShortTermBankLoansAndNotesPayable / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  | 7 us-gaap_NumberOfRealEstateProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember | 2 us-gaap_NumberOfRealEstateProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |
Potential future capital contributions under joint ventures which are not contractually binding | 100,000,000 bdn_Potentialfuturecapitalcontributionsunderjointventureswhicharenotcontractuallybinding / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investments, Cash contributions | 69,000,000 bdn_EquitymethodinvestmentsCashcontributions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  | 12,800,000 bdn_EquitymethodinvestmentsCashcontributions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |
Equity method investments, Closing costs | 200,000 bdn_EquitymethodinvestmentsClosingcosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  | 100,000 bdn_EquitymethodinvestmentsClosingcosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company's share of equity (Company's basis) | 40,374,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Two Tower Bridge [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company's share of equity (Company's basis) |  |  |  |  |  |  |  | (100,000)us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TwoTowerBridgeMember |  |  |  |  |  |  |  |
Net gain on real estate venture transactions |  | 3,683,000 us-gaap_NonmonetaryTransactionGainLossRecognizedOnTransfer / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TwoTowerBridgeMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investments, Fair Value Disclosure |  |  |  |  |  |  |  | 3,600,000 us-gaap_InvestmentsFairValueDisclosure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TwoTowerBridgeMember |  |  |  |  |  |  |  |
4040 Wilson Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of Real Estate Property |  |  |  |  |  |  | 426,900 us-gaap_AreaOfRealEstateProperty / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Budgeted Total Project Cost |  |  |  |  |  |  | 194,600,000 bdn_EquityMethodInvestmentBudgetedTotalProjectCost / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  |  |  |  | 72,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
Guaranty Percentage | 100.00%bdn_GuarantyPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company's share of equity (Company's basis) | 27,415,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of undeveloped parcels of land (in acres) owned by a Real Estate Venture |  |  |  |  |  |  | 1.3 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
Six Tower Bridge [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain (loss) on sale of undepreciated real estate |  | 7,800,000 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value |  |  |  |  |  |  |  | 24,500,000 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |
Business Acquisition Purchase Price Allocation Building |  |  |  |  |  |  |  | 14,800,000 bdn_BusinessAcquisitionPurchasePriceAllocationBuilding / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |
Business Acquisition Purchase Price Allocation, Land Portion |  |  |  |  |  |  |  | 6,900,000 bdn_BusinessAcquisitionPurchasePriceAllocationLandPortion / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |
Business Acquisition Purchase Price Allocation Intangible Assets |  |  |  |  |  |  |  | 3,300,000 bdn_BusinessAcquisitionPurchasePriceAllocationIntangibleAssets / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |
Business Acquisition Purchase Price Allocated To Market Lease Liabilities |  |  |  |  |  |  |  | 500,000 bdn_BusinessAcquisitionPurchasePriceAllocatedToMarketLeaseLiabilities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SixTowerBridgeMember |  |  |  |  |  |  |  |
The Grove at Cira Centre South [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investments, Cash contributions | 0 bdn_EquitymethodinvestmentsCashcontributions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors of a building |  |  |  |  |  |  |  |  |  |  |  |  | 33 bdn_NumberOfFloorsOfBuilding / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Student housing bed capacity |  |  |  |  |  |  |  |  |  |  |  |  | 850 bdn_StudentHousingBedCapacity / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Equity Method Investment, Budgeted Total Project Cost | 158,500,000 bdn_EquityMethodInvestmentBudgetedTotalProjectCost / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments | 60,700,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction Loan | 97,800,000 bdn_DevelopmentCostsContemplatedDebtFinancing / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Aggregate Cost |  |  |  |  |  |  |  |  |  |  |  |  | 4,000,000 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Area of undeveloped parcels of land (in acres) owned by a Real Estate Venture |  |  |  |  |  |  |  |  |  |  |  |  | 1 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Equity Method Investment, Underlying Equity in Net Assets |  |  |  |  |  |  |  |  |  |  |  |  | 8,500,000 us-gaap_EquityMethodInvestmentUnderlyingEquityInNetAssets / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  |  |  |  |  |  |  |  |  |  | 4,500,000 us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
TB-BDN Plymouth Apartments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guaranty Liabilities | 3,200,000 us-gaap_GuarantyLiabilities / dei_LegalEntityAxis = bdn_TbBdnPlymouthApartmentsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PJP VII [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guaranty Liabilities | 500,000 us-gaap_GuarantyLiabilities / dei_LegalEntityAxis = bdn_PjpViiMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
The Grove at Cira Centre South [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guaranty Liabilities | 24,700,000 us-gaap_GuarantyLiabilities / dei_LegalEntityAxis = bdn_GroveAtCiraCentreSouthMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Third Parties and Real Estate Ventures [Member] | Brandywine Nineteen Nineteen Ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / bdn_JointVentureMembersAxis = bdn_ThirdPartiesAndRealEstateVenturesMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |
LCOR/Calstrs [Member] | Brandywine Nineteen Nineteen Ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate gross sales price of a joint venture |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,400,000 bdn_Aggregategrosssalespriceofajointventure / bdn_JointVentureMembersAxis = bdn_LCORCalstrsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |
General Partners' Contributed Capital |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,200,000 us-gaap_GeneralPartnersContributedCapital / bdn_JointVentureMembersAxis = bdn_LCORCalstrsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |
Equity method investments, Cash contributions | 13,400,000 bdn_EquitymethodinvestmentsCashcontributions / bdn_JointVentureMembersAxis = bdn_LCORCalstrsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from the contribution of land to an unconsolidated real estate venture | 8,200,000 bdn_Netproceedsfromthecontributionoflandtoanunconsolidatedrealestateventure / bdn_JointVentureMembersAxis = bdn_LCORCalstrsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ashton Park [Member] | 4040 Wilson Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of land, net of amount encumbered |  |  |  |  |  |  | 36,000,000 bdn_Fairvalueoflandnetofamountencumbered / bdn_JointVentureMembersAxis = bdn_AshtonParkMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
Brandywine Realty Trust [Member] | Austin, Texas [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment, agreement to pay future capital expenditures | 4,400,000 bdn_Equitymethodinvestmentagreementtopayfuturecapitalexpenditures / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinTexasMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Brandywine Realty Trust [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties contributed to a joint venture |  |  |  |  |  |  |  |  | 7 bdn_Numberofpropertiescontributedtoajointventure / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Area of Real Estate Property |  |  |  |  |  |  |  |  | 1,398,826 us-gaap_AreaOfRealEstateProperty / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Aggregate gross sales price of a joint venture |  |  |  |  |  |  |  |  | 330,000,000 bdn_Aggregategrosssalespriceofajointventure / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Equity method investment, agreement to pay future capital expenditures |  | 800,000 bdn_Equitymethodinvestmentagreementtopayfuturecapitalexpenditures / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  | 5,200,000 bdn_Equitymethodinvestmentagreementtopayfuturecapitalexpenditures / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Equity method investments, Cash contributions |  |  |  |  | 18,900,000 bdn_EquitymethodinvestmentsCashcontributions / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember | 6,400,000 bdn_EquitymethodinvestmentsCashcontributions / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |
Net gain (loss) on real estate venture transactions |  | 25,900,000 bdn_NetGainLossOnRealEstateVentureTransactions / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Additional Distribution Rights | 10.00%bdn_EquityMethodInvestmentAdditionalDistributionRights / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Brandywine Realty Trust [Member] | 4040 Wilson Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Interest in Joint Venture | 26,800,000 us-gaap_PaymentsToAcquireInterestInJointVenture / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  | 36,000,000 us-gaap_PaymentsToAcquireInterestInJointVenture / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |  |
DRA Advisors LLC [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Distribution, Net of Initial Funding Agreement |  |  |  |  |  |  |  |  | 266,300,000 bdn_EquityMethodInvestmentDistributionNetofInitialFundingAgreement / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Amount Of Participant Contribution |  |  |  |  |  |  |  |  | 49,700,000 bdn_AmountOfParticipantContribution / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Equity method investments, Closing costs |  |  |  |  |  |  |  |  | 1,900,000 bdn_EquitymethodinvestmentsClosingcosts / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Closing Prorations and Lender Holdbacks |  |  |  |  |  |  |  |  | 6,900,000 bdn_ClosingProrationsandLenderHoldbacks / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Proceeds from Equity Method Investment, Dividends or Distributions |  |  |  |  |  |  |  |  | 271,500,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-Recourse Debt |  |  |  |  |  |  |  |  | 230,600,000 us-gaap_NonRecourseDebt / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |
Campus Crest Properties, LLC [Member] | The Grove at Cira Centre South [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  | 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / bdn_JointVentureMembersAxis = bdn_CampusCrestPropertiesLlcMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
HSRE, LLC [Member] [Member] | The Grove at Cira Centre South [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  | 40.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / bdn_JointVentureMembersAxis = bdn_HsreLlcMemberMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GroveAtCiraCentreSouthMember |  |  |
Four Points Centre [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  |  |  |  |  |  | 2 us-gaap_NumberOfRealEstateProperties / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember |  |  |  |  |  |
Number of floors of a building |  |  |  |  |  |  |  |  |  | 3 bdn_NumberOfFloorsOfBuilding / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember |  |  |  |  |  | 3 bdn_NumberOfFloorsOfBuilding / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember
Four Points Centre [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-Recourse Debt |  |  |  |  |  |  |  |  |  | 29,000,000 us-gaap_NonRecourseDebt / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |
Four Points Centre [Member] | Brandywine Realty Trust [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate gross sales price of a joint venture |  |  |  |  |  |  |  |  |  | 41,500,000 bdn_Aggregategrosssalespriceofajointventure / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |
Amount Of Participant Contribution |  |  |  |  |  |  |  |  |  | 5,900,000 bdn_AmountOfParticipantContribution / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |
Proceeds from Equity Method Investment, Dividends or Distributions |  |  |  |  |  |  |  |  |  | 34,400,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember / bdn_JointVentureMembersAxis = bdn_BrandywineRealtyTrustMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |
Four Points Centre [Member] | DRA Advisors LLC [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Participant Contribution |  |  |  |  |  |  |  |  |  | $ 5,900,000 bdn_AmountOfParticipantContribution / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = bdn_FourPointsCentreMember / bdn_JointVentureMembersAxis = bdn_DRAAdvisorsLLCMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |

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- Definition Aggregate approximate area of office buildings. + References No definition available. + Details
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- Definition Area Owned By Real Estate Venture in Parcels Of Land Under Development + References No definition available. + Details
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- Definition Equity method investment, agreement to pay future capital expenditures + References No definition available. + Details
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- Definition Number of apartment units in a Real Estate Venture. + References No definition available. + Details
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- Definition Number of office buildings in Real Estate Ventures. + References No definition available. + Details
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- Definition Number of real estate ventures developed hotel property + References No definition available. + Details
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- Definition Number of real estate ventures that owns buildings. + References No definition available. + Details
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- Definition Number of rooms contain in one real estate venture developed as Hotel Property. + References No definition available. + Details
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- Definition Number of unconsolidated investments in Real Estate Ventures. + References No definition available. + Details
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- Definition Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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