Commitments And Contingencies (Construction Projects) (Narrative) (Details)
 9 Months Ended 18 Months Ended
Oct. 06, 2015
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Apr. 01, 2015
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Sep. 30, 2016
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Sep. 30, 2015
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Sep. 30, 2016
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Dec. 31, 2015
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Commitments And Contingencies [Line Items]            
Amount outstanding     $ 95,000,000   $ 95,000,000 $ 155,000,000
Investment in unconsolidated joint ventures     31,318,000 $ 68,468,000    
Development of rental property     150,592,000 49,959,000    
Purchase price of property     $ 94,017,000 $ 59,700,000    
Eastchester Project [Member]            
Commitments And Contingencies [Line Items]            
Percentage of interest in venture     76.25%   76.25%  
Costs of the project incurred     $ 20,100,000      
Delivery date to tenant     fourth quarter of 2016      
Number of units | item     108   108  
Project costs incurred to date     $ 49,400,000   $ 49,400,000  
Amount of project costs funded by members     24,000,000   24,000,000  
Total project costs     53,100,000      
Amount to fund     3,900,000   3,900,000  
City Square Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred         23,900,000  
Total project costs     90,500,000      
Purchase price of property   $ 3,100,000        
Contingent consideration   $ 1,250,000        
Amount to fund     $ 8,600,000   $ 8,600,000  
City Square Project Phase One [Member]            
Commitments And Contingencies [Line Items]            
Delivery date to tenant     fourth quarter 2017      
Number of units | item       237    
Signature Place Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred     $ 12,900,000      
Delivery date to tenant     fourth quarter of 2017      
Number of units | item     197   197  
Project costs incurred to date     $ 13,100,000   $ 13,100,000  
Total project costs     58,700,000      
Amount to fund     13,100,000   $ 13,100,000  
Portside 5/6 Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred     $ 26,000,000      
Delivery date to tenant     first quarter of 2018      
Number of units | item     296   296  
Project costs incurred to date     $ 27,700,000   $ 27,700,000  
Total project costs     $ 111,400,000.000000      
City Square Project Phase Two [Member]            
Commitments And Contingencies [Line Items]            
Number of properties | item     128   128  
Delivery date to tenant     third quarter 2018      
Maximum borrowing capacity     $ 58,000,000   $ 58,000,000  
Riverhouse 11 Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred     25,800,000      
Total project costs     46,000,000      
51 Washington Street Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred     $ 32,100,000      
Delivery date to tenant     fourth quarter of 2018      
Construction Loan [Member] | Eastchester Project [Member]            
Commitments And Contingencies [Line Items]            
Maximum borrowing capacity     $ 28,800,000   28,800,000  
Amount outstanding     25,200,000   25,200,000  
Construction Loan [Member] | City Square Project [Member]            
Commitments And Contingencies [Line Items]            
Maximum borrowing capacity     41,500,000   41,500,000  
Amount outstanding     0   0  
Construction Loan [Member] | Signature Place Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     42,000,000   42,000,000  
Construction Loan [Member] | Riverhouse 11 Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     78,000,000   78,000,000  
Construction Loan [Member] | 51 Washington Street Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     54,000,000   54,000,000  
Development Property [Member] | Signature Place Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     16,700,000   16,700,000  
Development Property [Member] | Portside 5/6 Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     27,700,000   $ 27,700,000  
Development Property [Member] | Chase II Project [Member]            
Commitments And Contingencies [Line Items]            
Costs of the project incurred     $ 26,900,000      
Delivery date to tenant     fourth quarter of 2016      
Number of units | item     1,034   1,034  
Total project costs     $ 74,900,000      
Amount to fund     $ 0   $ 0  
Development Property [Member] | Chase II Project, Initial Phase [Member]            
Commitments And Contingencies [Line Items]            
Number of units | item       292    
Development Property [Member] | Riverhouse 11 Project [Member]            
Commitments And Contingencies [Line Items]            
Delivery date to tenant     first quarter 2018      
Number of units | item     295   295  
Project costs incurred to date     $ 33,000,000   $ 33,000,000  
Total project costs     $ 124,000,000      
Development Property [Member] | 51 Washington Street Project [Member]            
Commitments And Contingencies [Line Items]            
Number of properties | item     310   310  
Costs of the project incurred     $ 19,500,000      
Total project costs     86,100,000      
Development Property [Member] | Construction Loan [Member] | Chase II Project [Member]            
Commitments And Contingencies [Line Items]            
Maximum borrowing capacity     48,000,000   $ 48,000,000  
Amount outstanding     23,600,000   $ 23,600,000  
Unconsolidated Joint Venture Hotel [Member]            
Commitments And Contingencies [Line Items]            
Percentage of interest in venture 90.00%          
Development costs     $ 8,400,000      
Number of units | item     350   350  
Amount to fund     $ 0   $ 0  
Unconsolidated Joint Venture Hotel [Member] | Portside 5/6 Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     38,400,000   38,400,000  
Unconsolidated Joint Venture Hotel [Member] | XS Port Imperial Hotel, LLC [Member]            
Commitments And Contingencies [Line Items]            
Number of units | item 372          
Ownership percentage of third party venture 10.00%          
Unconsolidated Joint Venture Hotel [Member] | Port Imperial Hotel [Member]            
Commitments And Contingencies [Line Items]            
Total project costs $ 105,900,000          
Unconsolidated Joint Venture Hotel [Member] | Construction Loan [Member] | Portside 5/6 Project [Member]            
Commitments And Contingencies [Line Items]            
Amount to fund     73,000,000   73,000,000  
Unconsolidated Joint Venture Hotel [Member] | Construction Loan [Member] | Port Imperial Hotel [Member]            
Commitments And Contingencies [Line Items]            
Amount outstanding     $ 8,300,000   $ 8,300,000  
Amount to fund $ 94,000,000