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Summary of Significant Accounting Policies (Income Taxes) (Details) (USD $) In Billions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2011 | Dec. 31, 2010
Income Tax Contingency [Line Items] |  |
Distributable income minimum percentage | 90.00% |
Tax basis of assets | $ 4.5 | $ 4.5
Amount of Federal excise tax if sufficient taxable income is not distributed within prescribed time limits | 4.00% |
Excise tax annual amount, if certain requirements are not meant | 4.00% |
Excise tax, if sum of ordinary income is less than | 85.00% |
Excise tax, if Net capital gain exceeds cash distributions and certain taxes paid | 95.00% |
BRANDYWINE OPERATING PARTNERSHIP, L.P. |  |
Income Tax Contingency [Line Items] |  |
Tax basis of assets | $ 4.5 | $ 4.5
Amount of Federal excise tax if sufficient taxable income is not distributed within prescribed time limits | 4.00% |
Excise tax annual amount, if certain requirements are not meant | 4.00% |
Excise tax, if sum of ordinary income is less than | 85.00% |
Excise tax, if Net capital gain exceeds cash distributions and certain taxes paid | 95.00% |

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