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Summary of Significant Accounting Policies Income Taxes (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Tax Contingency [Line Items] |  |  |
Increase In Revenue Due To Amortization Of Deferred Rent | $ 2,400,000 bdn_IncreaseInRevenueDueToAmortizationOfDeferredRent | $ 2,400,000 bdn_IncreaseInRevenueDueToAmortizationOfDeferredRent | $ 2,400,000 bdn_IncreaseInRevenueDueToAmortizationOfDeferredRent
Distributable Income Minimum Percentage | 90.00%bdn_DistributableIncomeMinimumPercentage |  |
Federal excise tax if sufficient taxable income is not distributed within prescribed time limits | 4.00%bdn_FederalExciseTaxIfSufficientTaxableIncomeIsNotDistributedWithinPrescribedTimeLimits |  |
Excise tax equal to annual amount | 4.00%bdn_ExciseTaxEqualToAnnualAmount |  |
Excise tax, if sum of ordinary income | 85.00%bdn_ExciseTaxIfSumOfOrdinaryIncome |  |
Excise tax, if Net capital gain exceeds cash distributions and certain taxes paid | 95.00%bdn_ExciseTaxIfNetCapitalGainExceedsCashDistributionsAndCertainTaxesPaid |  |
Tax Basis of Assets, Cost for Income Tax Purposes | 3,700,000,000 us-gaap_RealEstateFederalIncomeTaxBasis | 4,000,000,000 us-gaap_RealEstateFederalIncomeTaxBasis |
BRANDYWINE OPERATING PARTNERSHIP, L.P. |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax Basis of Assets, Cost for Income Tax Purposes | $ 3,700,000,000 us-gaap_RealEstateFederalIncomeTaxBasis / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | $ 4,000,000,000 us-gaap_RealEstateFederalIncomeTaxBasis / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |

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