Investments In Unconsolidated Joint Ventures (Summary Of Company's Equity In Earnings (Loss) Of Unconsolidated Joint Ventures) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures $ (834) $ 21,790 $ (614) $ (1,554) $ (449) $ 3,135 $ (2,329) $ (3,529) $ 18,788 $ (3,172) $ (2,423)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Marbella RoseGarden, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 231 231 (19)
Unconsolidated Joint Venture Multi-Family Properties [Member] | RoseGarden Monaco Holdings, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (937) (1,224) (1,040)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Rosewood Morristown, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (317) (364) (345)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Riverwalk G Urban Renewal, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (1,146) (955) (2,139)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Elmajo Urban Renewal Associates, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                     (203)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Crystal House Apartments Investors LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (870) (123) (139)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Roseland/Port Imperial Partners, L.P. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (120) (474) (646)
Unconsolidated Joint Venture Multi-Family Properties [Member] | RoseGarden Marbella South, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (202)    
Unconsolidated Joint Venture Multi-Family Properties [Member] | Estuary Urban Renewal Unit B, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                   1 (15)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Riverpark At Harrison I, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (190) (363) (150)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Capitol Place Mezz LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (2,440) (3,687) (75)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Harborside Unit A Urban Renewal, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (219)   (218)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Grand Jersey Waterfront URA, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (80) (32) (54)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Hillsborough 206 Holdings, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (53) (5) (10)
Unconsolidated Joint Venture Multi-Family Properties [Member] | Plaza VIII & IX Associates, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 393 344 320
Unconsolidated Joint Venture Office Buildings [Member] | Red Bank Corporate Plaza, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 448 392 380
Unconsolidated Joint Venture Office Buildings [Member] | 12 Vreeland Associates, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 347 270 106
Unconsolidated Joint Venture Office Buildings [Member] | BNES Associates III [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (15) 115 240
Unconsolidated Joint Venture Office Buildings [Member] | KPG-P 100 IMW JV, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                   (800) (1,887)
Unconsolidated Joint Venture Office Buildings [Member] | Keystone-Penn [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 600 3,812  
Unconsolidated Joint Venture Office Buildings [Member] | Keystone-TriState [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (1,672) (2,182) (318)
Unconsolidated Joint Venture Office Buildings [Member] | KPG-MCG Curtis JV, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (92) 475 624
Unconsolidated Joint Venture Other Property [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 18,788 (3,172) (2,423)
Unconsolidated Joint Venture Other Property [Member] | Roseland/North Retail, L.L.C. [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 (52) (70) (102)
Unconsolidated Joint Venture Other Property [Member] | South Pier At Harborside [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 24,180 3,036 2,602
Unconsolidated Joint Venture Other Property [Member] | Other [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Company's equity in earnings of unconsolidated joint ventures                 $ 994 $ (1,569) $ 665