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
 3 Months Ended
Mar. 31, 2018
USD ($)
item
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
item
Dec. 31, 2015
item
Commitments And Contingencies [Line Items]          
Number of units | item 365        
Amount outstanding $ 863,738   $ 822,288    
Investment in unconsolidated joint ventures 1,266 $ 6,625      
XS Hotel Urban Renewal Associates LLC [Member]          
Commitments And Contingencies [Line Items]          
Percentage of interest in venture         90.00%
Costs of the project incurred $ 113,200        
Delivery date to tenant second quarter 2018        
Number of units | item         372
Total project costs $ 142,500        
250 Johnson Road [Member]          
Commitments And Contingencies [Line Items]          
Costs of the project incurred $ 57,700        
Delivery date to tenant second 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 $ 94,900        
Delivery date to tenant second quarter 2018        
Number of units | item 296        
Total project costs $ 111,400        
Port Imperial South 11 [Member]          
Commitments And Contingencies [Line Items]          
Costs of the project incurred $ 94,300        
Delivery date to tenant second quarter 2018        
Number of units | item 295        
Total project costs $ 122,000        
Construction Loan [Member] | XS Hotel Urban Renewal Associates LLC [Member]          
Commitments And Contingencies [Line Items]          
Maximum borrowing capacity 94,000        
Amount outstanding 51,000        
Construction Loan [Member] | 250 Johnson Road [Member]          
Commitments And Contingencies [Line Items]          
Amount outstanding 37,000        
Amount to fund 42,000        
Construction Loan [Member] | Portside 5/6 [Member]          
Commitments And Contingencies [Line Items]          
Amount outstanding 56,500        
Amount to fund 73,000        
Construction Loan [Member] | Port Imperial South 11 [Member]          
Commitments And Contingencies [Line Items]          
Amount outstanding 54,300        
Amount to fund 78,000        
Development Property [Member] | Port Imperial South 11 [Member]          
Commitments And Contingencies [Line Items]          
Costs of the project incurred 38,100        
Amount to fund $ 44,000        
Unconsolidated Joint Venture Hotel [Member]          
Commitments And Contingencies [Line Items]          
Number of units | item 350