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Discontinued Operations (Details Textuals) | 12 Months Ended
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Dec. 31, 2011 Properties | Dec. 31, 2010 Properties | Dec. 31, 2009 Properties
Discontinued Operations (Textuals) [Abstract] |  |  |
Number of properties sold (in properties) | 19 | 19 | 19
Discontinued Operations [Member] |  |  |
Discontinued Operations (Textuals) [Abstract] |  |  |
Net rentable square feet of properties sold (in square feet) | 1,600,000 |  |

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- Definition Net Rentable Space Sold. + References No definition available. + Details
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- Definition Number of properties sold. + References No definition available. + Details
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