Properties, Net (Details 2) - USD ($) $ in Thousands  | 
Sep. 30, 2018  | 
Dec. 31, 2017  | 
|---|---|---|
| Properties | ||
| Projects in development or held for future development | $ 410,850 | $ 403,494 | 
| Projects in development or held for future development | ||
| Properties | ||
| Projects in development or held for future development | 410,850 | 403,494 | 
| Projects in development or held for future development | Land | ||
| Properties | ||
| Projects in development or held for future development | 220,468 | 240,825 | 
| Projects in development or held for future development | Development in progress, excluding land | ||
| Properties | ||
| Projects in development or held for future development | $ 190,382 | $ 162,669 | 
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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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