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Subsequent Events (Details Textuals) (USD $) In Millions, unless otherwise specified | 9 Months Ended |
--- | --- | ---
Sep. 30, 2011 Property Tenants Year sqft | Sep. 30, 2010 | Oct. 28, 2011 sqft
Subsequent Events (Textuals) [Abstract] |  |  |
Number of office properties sold | 2 |  |
Aggregate square footage of properties sold |  |  | 206,243
Aggregate sale price of properties sold |  | $ 22.8 |
Five Greentree Centre [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Percentage Occupancy of Properties Sold |  |  | 96.10%
Lake Center Two Member |  |  |
Subsequent Event [Line Items] |  |  |
Percentage Occupancy of Properties Sold |  |  | 47.80%

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- Definition Aggregate Sale Price Of Properties Sold. + Details
Name: | bdn_AggregateSalePriceOfPropertiesSold
Namespace Prefix: | bdn
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Total square footage of properties sold subsequent to balance sheet date. + Details
Name: | bdn_AggregateSquareFootageOfPropertiesSold
Namespace Prefix: | bdn
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of office properties sold. + Details
Name: | bdn_NumberOfOfficePropertiesSold
Namespace Prefix: | bdn
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage occupancy of properties sold at date of sale. + Details
Name: | bdn_PercentageOccupancyOfPropertiesSold
Namespace Prefix: | bdn
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Subsequent Events. + Details
Name: | bdn_SubsequentEventsDetailsTextualsAbstract
Namespace Prefix: | bdn
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration