Properties, net (Details) - USD ($) $ in Thousands  | 
Dec. 31, 2016  | 
Dec. 31, 2015  | 
Dec. 31, 2014  | 
Dec. 31, 2013  | 
|---|---|---|---|---|
| Properties | ||||
| Gross | $ 3,874,715 | $ 4,158,616 | $ 4,014,336 | $ 3,811,950 | 
| Operating properties, net | 2,671,831 | 2,920,529 | ||
| Operating properties, net [Member] | ||||
| Properties | ||||
| Less: accumulated depreciation | (706,385) | (700,363) | ||
| Operating properties, net | 2,671,831 | 2,920,529 | ||
| Operating properties, net [Member] | Land [Member] | ||||
| Properties | ||||
| Gross | 433,311 | 463,305 | ||
| Operating properties, net [Member] | Buildings and improvements [Member] | ||||
| Properties | ||||
| Gross | $ 2,944,905 | $ 3,157,587 | 
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- Definition Amount, before accumulated depreciation, of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate. 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 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. No definition available. 
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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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