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Fair Value of Financial Instruments (Details Textuals) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 Properties | Dec. 31, 2010 Properties | Dec. 31, 2009 Properties
Fair Value of Financial Instruments (Textuals) [Abstract] |  |  |
Number of properties sold (in properties) | 19 | 19 | 19
Trenton Properties [Member] |  |  |
Fair Value of Financial Instruments (Textuals) [Abstract] |  |  |
Gross deferred gain on sale of properties | 12.9 |  |
Number of properties sold (in properties) | 2 |  |

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- Details
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Namespace Prefix: | bdn_
Data Type: | xbrli:stringItemType
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- Definition Number of properties sold. + References No definition available. + Details
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Namespace Prefix: | bdn_
Data Type: | xbrli:integerItemType
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- Definition Amount of gain on the sale of property that does not qualify for gain recognition as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 40 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.U.Q2) -URI http://asc.fasb.org/extlink&oid=6955272&loc=d3e221323-122791 + Details
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Balance Type: | credit
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