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Investment in Unconsolidated Ventures Company's Investment in Real Estate Ventures and the Company's Share of the Real Estate Ventures' Income (Loss) (Details) (USD $) | 12 Months Ended |  |  |  |  |  |
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Dec. 31, 2014 acre | Dec. 31, 2013 | Dec. 31, 2012 | Jul. 31, 2013 acre | Jul. 31, 2014 | Mar. 26, 2013 | Jan. 20, 2011 acre | Jun. 19, 2013 | Apr. 03, 2014
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land | 3.0 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand |  |  |  |  |  |  |  |
Equity Method Investments | $ 225,004,000 us-gaap_EquityMethodInvestments | $ 180,512,000 us-gaap_EquityMethodInvestments | $ 193,555,000 us-gaap_EquityMethodInvestments |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (790,000)us-gaap_IncomeLossFromEquityMethodInvestments | 3,664,000 us-gaap_IncomeLossFromEquityMethodInvestments | 2,741,000 us-gaap_IncomeLossFromEquityMethodInvestments |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 965,077,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt |  |  |  |  |  |  |  |
Equity Method Investments including net liabilities | 223,790,000 bdn_EquityMethodInvestmentsincludingnetliabilities |  |  |  |  |  |  |  |
Equity Method Investments [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 965,077,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvestmentsMember |  |  |  |  |  |  |  |
Broadmoor Austin Associates [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BroadmoorAustinAssociatesMember |  |  |  |  |  |  |  |
Equity Method Investments | 65,407,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BroadmoorAustinAssociatesMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (460,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BroadmoorAustinAssociatesMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 53,516,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BroadmoorAustinAssociatesMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 7.04%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BroadmoorAustinAssociatesMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Apr. 10, 2023 |  |  |  |  |  |  |  |
HSRE, LLC [Member] [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_HsreLlcMemberMember |  |  |  |  |  |  |  |
Equity Method Investments | 14,314,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_HsreLlcMemberMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 67,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_HsreLlcMemberMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 90,245,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_HsreLlcMemberMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms | L+2.20% |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Jul. 25, 2016 |  |  |  |  |  |  |  |
4040 Wilson Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land |  |  |  | 1.3 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |
Equity Method Investments | 27,415,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (132,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 0 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_A4040WilsonVentureMember |  |  |  |  |  |  |  |
Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Equity Method Investments | 45,712,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (185,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 133,843,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.93%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Equity Method Investments | 40,374,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (574,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 382,100,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  | 34,500,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.57%us-gaap_DebtInstrumentInterestRateEffectivePercentage / 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 |  |  |  |
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 |  |  |
Equity Method Investments |  |  |  |  |  | 17,000,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BdnBeaconVentureLlcMember |  |  |
TB-BDN Plymouth Apartments [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TbBdnPlymouthApartmentsMember |  |  |  |  |  |  |  |
Equity Method Investments | 12,720,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TbBdnPlymouthApartmentsMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (83,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TbBdnPlymouthApartmentsMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 29,481,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TbBdnPlymouthApartmentsMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms | L+1.70% |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Dec. 20, 2017 |  |  |  |  |  |  |  |
Brandywine Nineteen Nineteen Ventures [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land |  |  |  |  |  |  | 1 bdn_AreaOwnedByRealEstateVentureOfUndevelopedParcelsOfLand / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |
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 |  |
Equity Method Investments | 12,823,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (21,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 0 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms | L+2.25% |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Oct. 21, 2018 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms | LIBOR + 2.25% |  |  |  |  |  |  |  |
Interest rate upon receipt of certificate of occupancy | 2.00%bdn_Interestrateuponreceiptofcertificateofoccupancy / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
Interest rate upon stabilization | 1.75%bdn_Interestrateuponstabilization / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
Interest rate protection cap | 4.50%bdn_Interestrateprotectioncap / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineNineteenNineteenVenturesMember |  |  |  |  |  |  |  |
One Thousand Chesterbrook Blvd. [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_OneThousandChesterbrookBlvdMember |  |  |  |  |  |  |  |
Equity Method Investments | 2,152,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_OneThousandChesterbrookBlvdMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 388,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_OneThousandChesterbrookBlvdMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 24,251,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_OneThousandChesterbrookBlvdMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 4.75%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_OneThousandChesterbrookBlvdMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Dec. 01, 2021 |  |  |  |  |  |  |  |
Four Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 65.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_FourTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investments | 1,474,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_FourTowerBridgeMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (144,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_FourTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 10,353,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_FourTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 5.20%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_FourTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Feb. 10, 2021 |  |  |  |  |  |  |  |
Residence Inn Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_ResidenceInnTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investments | 723,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_ResidenceInnTowerBridgeMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 107,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_ResidenceInnTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 13,394,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_ResidenceInnTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 5.63%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_ResidenceInnTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Feb. 11, 2016 |  |  |  |  |  |  |  |
PJP VII [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpViiMember |  |  |  |  |  |  |  |
Equity Method Investments | 911,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpViiMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 177,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpViiMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 5,785,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpViiMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms | L+2.65% |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Dec. 31, 2019 |  |  |  |  |  |  |  |
PJP Two [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpTwoMember |  |  |  |  |  |  |  |
Equity Method Investments | 403,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpTwoMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 73,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpTwoMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 3,492,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpTwoMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 6.12%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpTwoMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Nov. 01, 2023 |  |  |  |  |  |  |  |
G&I Interchange Office LLC (DRA — N. PA) [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Equity Method Investments | 0 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (658,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 174,595,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 5.78%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Feb. 28, 2015 |  |  |  |  |  |  |  |
Sale of ownership in properties | 80.00%bdn_SaleOfOwnershipInProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_GiInterchangeOfficeLlcDraNPaMember |  |  |  |  |  |  |  |
Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investments | 315,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (388,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 14,865,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.78%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
PJP Five [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpFiveMember |  |  |  |  |  |  |  |
Equity Method Investments | 216,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpFiveMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 166,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpFiveMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 5,242,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpFiveMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 6.47%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpFiveMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Aug. 11, 2019 |  |  |  |  |  |  |  |
Two Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investments |  |  |  |  |  |  |  | (100,000)us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_TwoTowerBridgeMember |
PJP Six [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpSixMember |  |  |  |  |  |  |  |
Equity Method Investments | 45,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpSixMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (67,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpSixMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 8,168,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpSixMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 6.08%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_PjpSixMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Apr. 01, 2023 |  |  |  |  |  |  |  |
Coppell Associates [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_CoppellAssociatesMember |  |  |  |  |  |  |  |
Equity Method Investments | (1,214,000)us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_CoppellAssociatesMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | (45,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_CoppellAssociatesMember |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 15,747,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_CoppellAssociatesMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 5.75%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_CoppellAssociatesMember |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date | Feb. 01, 2016 |  |  |  |  |  |  |  |
Invesco, L.P. [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investments | 0 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_InvescoLPMember |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 989,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_InvescoLPMember |  |  |  |  |  |  |  |
Secured Debt [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Long-term Debt, Weighted Average Interest Rate | 5.72%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember | 5.73%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember | 6.65%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember |  |  |  |  |  |
Secured Debt [Member] | Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Long-term Debt, Weighted Average Interest Rate | 3.93%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Long-term Debt, Weighted Average Interest Rate | 3.57%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Long-term Debt, Weighted Average Interest Rate | 3.78%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fifth mortgage - swapped to fixed [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 34,500,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FifthmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.87%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FifthmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed rate loan maturing January 2019 [Member] | Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 39,300,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingJanuary2019Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.40%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingJanuary2019Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed rate loan maturing January 2022 [Member] | Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 28,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingJanuary2022Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingJanuary2022Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed rate loan maturing August 2019 [Member] | Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 66,500,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingAugust2019Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.22%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedrateloanmaturingAugust2019Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | First mortgage - swapped to fixed [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 34,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FirstmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Fixed Interest Rate | 1.59%us-gaap_DerivativeFixedInterestRate / us-gaap_DebtInstrumentAxis = bdn_FirstmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Basis Spread on Variable Rate | 1.93%us-gaap_DerivativeBasisSpreadOnVariableRate / us-gaap_DebtInstrumentAxis = bdn_FirstmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.52%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_DebtInstrumentAxis = bdn_FirstmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Second mortgage - swapped to fixed [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 56,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_SecondmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Fixed Interest Rate | 1.49%us-gaap_DerivativeFixedInterestRate / us-gaap_DebtInstrumentAxis = bdn_SecondmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Basis Spread on Variable Rate | 1.70%us-gaap_DerivativeBasisSpreadOnVariableRate / us-gaap_DebtInstrumentAxis = bdn_SecondmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.19%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_DebtInstrumentAxis = bdn_SecondmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Third mortgage - swapped to fixed [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 140,600,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_ThirdmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Fixed Interest Rate | 1.43%us-gaap_DerivativeFixedInterestRate / us-gaap_DebtInstrumentAxis = bdn_ThirdmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Derivative, Basis Spread on Variable Rate | 2.01%us-gaap_DerivativeBasisSpreadOnVariableRate / us-gaap_DebtInstrumentAxis = bdn_ThirdmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.44%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_DebtInstrumentAxis = bdn_ThirdmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fourth mortgage - swapped to fixed [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | 29,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = bdn_FourthmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FourthmortgageswappedtofixedMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Mortgage Maturing February 2015 [Domain] | Brandywine - Al Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Number of Fixed Rate Mortgages | 3 bdn_DebtInstrumentNumberOfFixedRateMortgages / us-gaap_DebtInstrumentAxis = bdn_MortgageMaturingMarch2017Domain / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_BrandywineAlVentureMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Mortgage Maturing February 2015 [Domain] | Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 8,000,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_DebtInstrumentAxis = bdn_MortgageMaturingMarch2017Domain / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Number of Fixed Rate Mortgages | 2 bdn_DebtInstrumentNumberOfFixedRateMortgages / us-gaap_DebtInstrumentAxis = bdn_MortgageMaturingMarch2017Domain / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_MortgageMaturingMarch2017Domain / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed Rate Loan Maturing September 2025 [Member] | Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 1,000,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingSeptember2025Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingSeptember2025Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed Rate Loan Maturing February 2016 [Member] | Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 2,000,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingFebruary2016Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingFebruary2016Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Secured Debt [Member] | Fixed Rate Loan Maturing March 2020 [Member] | Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Equity Method Investment Summarized Financial Information Debt | 3,900,000 bdn_EquityMethodInvestmentSummarizedfinancialinformationdebt / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingMarch2020Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 0.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = bdn_FixedRateLoanMaturingMarch2020Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SecuredDebtMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_SevenTowerBridgeMember |  |  |  |  |  |  |  |
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
Secured Debt [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 88,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_SecuredDebtMember |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bdn_AustinJointVentureMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_SecuredDebtMember |  |  |  |  |  |  |  |

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