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, 2017
USD ($)
item
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
item
Dec. 31, 2015
item
Commitments And Contingencies [Line Items]        
Amount outstanding $ 671,838   $ 634,069  
Investment in unconsolidated joint ventures 19,279 $ 31,318    
XS Hotel Urban Renewal Associates LLC [Member]        
Commitments And Contingencies [Line Items]        
Percentage of interest in venture       90.00%
Costs of the project incurred $ 87,600      
Delivery date to tenant second quarter 2018      
Number of units | item       372
Total project costs $ 139,400      
City Square Project [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred 70,600      
Total project costs $ 92,000      
City Square Project Phase One [Member]        
Commitments And Contingencies [Line Items]        
Delivery date to tenant first quarter 2018      
Number of units | item       237
City Square Project Phase Two [Member]        
Commitments And Contingencies [Line Items]        
Delivery date to tenant third quarter 2018      
Number of units | item       128
Signature Place Project [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred $ 45,000      
Delivery date to tenant first quarter of 2018      
Number of units | item     197  
Total project costs $ 58,700      
Portside 5/6 [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred $ 81,000      
Delivery date to tenant first quarter 2018      
Number of units | item 296      
Total project costs $ 111,400      
Riverhouse 11 Project [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred $ 72,800      
Delivery date to tenant first quarter 2018      
Number of units | item 295      
Total project costs $ 125,000      
51 Washington Street Project [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred $ 22,900      
Delivery date to tenant first quarter 2020      
Number of units | item 310      
Total project costs $ 89,400      
Construction Loan [Member] | XS Hotel Urban Renewal Associates LLC [Member]        
Commitments And Contingencies [Line Items]        
Maximum borrowing capacity 94,000      
Amount outstanding 31,000      
Construction Loan [Member] | City Square Project [Member]        
Commitments And Contingencies [Line Items]        
Maximum borrowing capacity 58,000      
Amount outstanding 27,800      
Construction Loan [Member] | Signature Place Project [Member]        
Commitments And Contingencies [Line Items]        
Amount outstanding 22,700      
Amount to fund 42,000      
Construction Loan [Member] | Portside 5/6 [Member]        
Commitments And Contingencies [Line Items]        
Amount outstanding 32,000      
Amount to fund 73,000      
Construction Loan [Member] | Riverhouse 11 Project [Member]        
Commitments And Contingencies [Line Items]        
Amount outstanding 37,800      
Amount to fund 78,000      
Development Property [Member] | Riverhouse 11 Project [Member]        
Commitments And Contingencies [Line Items]        
Costs of the project incurred 34,400      
Amount to fund $ 47,000      
Unconsolidated Joint Venture Hotel [Member]        
Commitments And Contingencies [Line Items]        
Number of units | item 350