| 
           Properties, net (Details 2) (USD $) 
        In Thousands, unless otherwise specified  | 
        
           Mar. 31, 2012 
         | 
        
           Dec. 31, 2011 
         | 
      
|---|---|---|
| Properties | ||
| Projects in development or held for future development | $ 633,968 | $ 638,919 | 
| 
           Projects in development or held for future development | Land in development or held for future development 
         | 
        ||
| Properties | ||
| Projects in development or held for future development | 225,085 | 229,833 | 
| 
           Projects in development or held for future development | Construction in progress, excluding land 
         | 
        ||
| Properties | ||
| Projects in development or held for future development | $ 408,883 | $ 409,086 | 
| X | ||||||||||
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- Definition 
          The current amount of expenditures for a real estate project that has not yet been completed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
          
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