| 
           Properties, net (Details) (USD $) 
        In Thousands  | 
        
           Jun. 30, 2011 
         | 
        
           Dec. 31, 2010 
         | 
      
|---|---|---|
| Properties | ||
| Operating properties, net | $ 2,741,433 | $ 2,802,773 | 
| 
           Operating properties 
         | 
        ||
| Properties | ||
| Less: accumulated depreciation | (527,616) | (503,032) | 
| 
           Operating properties | Land, operating properties 
         | 
        ||
| Properties | ||
| Gross | 491,188 | 501,210 | 
| 
           Operating properties | Buildings and improvements 
         | 
        ||
| Properties | ||
| Gross | $ 2,777,861 | $ 2,804,595 | 
| X | ||||||||||
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- 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. 
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- Definition 
          Gross amount of real estate as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          The cumulative amount of depreciation for real estate property held for investment purposes. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Carrying amount of income producing properties held for rental. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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