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           Organization (Tables) 
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        6 Months Ended | |||||||||||||||||||||||||
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           Jun. 30, 2011 
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| Organization. | ||||||||||||||||||||||||||
| Summary of forms of ownership and percentage of ownership forms | 
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| X | ||||||||||
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- Details 
          
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| X | ||||||||||
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- Definition 
          Tabular disclosure of operating partnership's forms of ownership and the percentage of ownership forms owned by the parent company. 
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