Quarterly report pursuant to Section 13 or 15(d)

Commitments And Contingencies (Construction Projects) (Narrative) (Details)

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Commitments And Contingencies (Construction Projects) (Narrative) (Details)
$ in Thousands
9 Months Ended
Sep. 30, 2018
USD ($)
item
Dec. 31, 2017
USD ($)
Dec. 31, 2015
item
Commitments And Contingencies [Line Items]      
Number of units | item 1,153    
Amount outstanding $ 870,313 $ 822,288  
XS Hotel Urban Renewal Associates LLC [Member]      
Commitments And Contingencies [Line Items]      
Percentage of interest in venture     90.00%
Costs of the project incurred $ 135,100    
Delivery date to tenant fourth quarter 2018    
Number of units | item     372
Total project costs $ 153,100    
Chase III, Overlook Ridge [Member]      
Commitments And Contingencies [Line Items]      
Costs of the project incurred $ 14,400    
Delivery date to tenant fourth quarter 2020    
Number of units | item 326    
Total project costs $ 99,900    
Amount to fund 37,900    
Building 8/9 [Member]      
Commitments And Contingencies [Line Items]      
Costs of the project incurred $ 29,700    
Delivery date to tenant fourth quarter 2020    
Number of units | item 313    
Total project costs $ 142,600    
Amount to fund 50,600    
Construction Loan [Member] | XS Hotel Urban Renewal Associates LLC [Member]      
Commitments And Contingencies [Line Items]      
Maximum borrowing capacity 94,000    
Amount outstanding 68,900    
Construction Loan [Member] | Chase III, Overlook Ridge [Member]      
Commitments And Contingencies [Line Items]      
Amount to fund 62,000    
Construction Loan [Member] | Building 8/9 [Member]      
Commitments And Contingencies [Line Items]      
Amount outstanding $ 92,000