| 
           Discontinued Operations (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| 
           Jun. 30, 2011 
         | 
        
           Jun. 30, 2010 
         | 
        
           Jun. 30, 2011 
         | 
        
           Jun. 30, 2010 
         | 
      |
| Discontinued Operations | ||||
| Number of operating properties held for sale | 17 | 17 | ||
| Revenue from real estate operations | $ 2,263 | $ 3,262 | $ 4,546 | $ 6,627 | 
| Property operating expenses | 733 | 884 | 1,928 | 2,234 | 
| Depreciation and amortization | 609 | 828 | 2,239 | 1,620 | 
| Impairment loss | 6,315 | 6,315 | ||
| Expenses from real estate operations | 7,657 | 1,712 | 10,482 | 3,854 | 
| Operating income from real estate operations | (5,394) | 1,550 | (5,936) | 2,773 | 
| Interest expense | (223) | (345) | (512) | (556) | 
| Gain on sales of real estate | 150 | 150 | 297 | |
| Discontinued operations | $ (5,467) | $ 1,205 | $ (6,298) | $ 2,514 | 
| X | ||||||||||
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- Definition 
          Amount, if any, of gain on sales of real estate allocated to the disposal group, including a component of the entity (discontinued operation), during the reporting period. 
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| X | ||||||||||
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- Definition 
          Amount of depreciation and amortization costs attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. 
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- Definition 
          Amount of property operating expenses attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. 
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- Definition 
          Represents the aggregate impairment loss recognized during the period related to properties expected to be disposed that are included in discontinued operations. 
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| X | ||||||||||
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- Definition 
          The number of operating real estate properties held for sale as of the balance sheet date. 
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- Details 
          
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| X | ||||||||||
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- Definition 
          Amount, if any, of interest expense allocated to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition 
          Amount of operating expenses attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition 
          Amount of operating income or loss attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition 
          Amount of sales or other form of revenues attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition 
          This element represents the overall income (loss) from a disposal group that is classified as a component of the entity, net of income tax, reported as a separate component of income before extraordinary items before deduction or consideration of the amount which may be allocable to noncontrolling interests, if any. Includes the following (net of tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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