Investments In Unconsolidated Joint Ventures (Summary Of Unconsolidated Joint Ventures) (Details)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2019
USD ($)
Sep. 30, 2020
USD ($)
ft²
item
Sep. 30, 2020
USD ($)
ft²
item
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Jun. 26, 2020
USD ($)
Jun. 10, 2020
USD ($)
Mar. 12, 2020
Aug. 01, 2019
Jan. 31, 2019
Schedule of Equity Method Investments [Line Items]                    
Carrying Value   $ 194,779 $ 194,779   $ 209,091          
Purchase price of property     123,785 $ 79,842            
Property impairments on continuing operations   $ 36,582 $ 36,582              
Minimum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership %   20.00% 20.00%              
Maximum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership %   85.00% 85.00%              
Crystal House [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity           $ 161,500        
Percentage of interest in developable land   50.00% 50.00%              
Number of units available for development | item   738 738              
PI North - Riverwalk C [Member] | Construction Loan [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity   $ 112,000 $ 112,000              
Percent of principal loan outstanding     10.00%              
Riverpark At Harrison [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity             $ 30,192      
Urby At Harborside [Member] | Construction/Permanent Loan [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership %   85.00% 85.00%              
PI North - Land [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   836 836              
Residual ownership interest   20.00% 20.00%              
Guaranteed amount   $ 22,000 $ 22,000              
Red Bank [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Gain on sale $ 900                  
12 Vreeland Road [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property impairments on continuing operations         3,700          
The Shops At 40 Park Property [Member] | Metropolitan And Lofts At 40 Park [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   50,973 50,973              
Balance   $ 6,067 $ 6,067              
Property Debt, Interest Rate, Spread Over LIBOR     0.0225%              
Residual ownership interest   25.00% 25.00%              
Mortgage loan, maturity month and year     October 2021              
Lofts At 40 Park Property [Member] | Metropolitan And Lofts At 40 Park [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   59 59              
Property Debt, Interest Rate, Spread Over LIBOR     0.015%              
Indirect ownership interest   50.00% 50.00%              
Number of stories | item   5 5              
Maximum borrowing capacity   $ 18,200 $ 18,200              
Mortgage loan, maturity month and year     January 2023              
Metropolitan Property [Member] | Metropolitan And Lofts At 40 Park [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Balance   $ 36,500 $ 36,500              
Property Debt, Interest Rate, Spread Over LIBOR     0.0285%              
Mortgage loan, maturity month and year     October 2023              
Unconsolidated Joint Venture Multi-Family Properties [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   2,611 2,611              
Unconsolidated Joint Venture Multi-Family Properties [Member] | Metropolitan And Lofts At 40 Park [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   189 189              
Company's Effective Ownership %   25.00% 25.00%              
Carrying Value   $ 3,746 $ 3,746   7,257          
Balance   $ 60,767 $ 60,767              
Unconsolidated Joint Venture Multi-Family Properties [Member] | RiverTrace At Port Imperial [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   316 316              
Company's Effective Ownership %   22.50% 22.50%              
Carrying Value   $ 6,808 $ 6,808   7,463          
Balance   $ 82,000 $ 82,000              
Property Debt, Maturity Date     Nov. 10, 2026              
Property Debt, Interest Rate   3.21% 3.21%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | Crystal House [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   825 825              
Company's Effective Ownership %   25.00% 25.00%              
Carrying Value   $ 26,844 $ 26,844   28,823          
Balance   $ 161,500 $ 161,500              
Property Debt, Maturity Date     Jul. 01, 2027              
Property Debt, Interest Rate   2.72% 2.72%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | PI North - Riverwalk C [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   360 360              
Company's Effective Ownership %   40.00% 40.00%              
Carrying Value   $ 35,946 $ 35,946   35,527          
Balance   $ 63,628 $ 63,628              
Property Debt, Maturity Date     Dec. 06, 2021              
Property Debt, Interest Rate   2.75% 2.75%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | Marbella II [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership %                 24.27% 50.00%
Unconsolidated Joint Venture Multi-Family Properties [Member] | Riverpark At Harrison [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   141 141              
Company's Effective Ownership %   45.00% 45.00%              
Carrying Value   $ 787 $ 787   1,015          
Balance   $ 30,192 $ 30,192              
Property Debt, Maturity Date     Jul. 01, 2035              
Property Debt, Interest Rate   3.19% 3.19%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | Station House [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   378 378              
Company's Effective Ownership %   50.00% 50.00%              
Carrying Value   $ 33,860 $ 33,860   35,676          
Balance   $ 95,576 $ 95,576              
Property Debt, Maturity Date     Jul. 01, 2033              
Property Debt, Interest Rate   4.82% 4.82%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | Urby At Harborside [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   762 762              
Company's Effective Ownership %   85.00% 85.00%              
Carrying Value   $ 74,847 $ 74,847   79,790          
Balance   $ 192,000 $ 192,000              
Property Debt, Maturity Date     Aug. 01, 2029              
Property Debt, Interest Rate   5.197% 5.197%              
Unconsolidated Joint Venture Multi-Family Properties [Member] | PI North - Land [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   836 836              
Company's Effective Ownership %   20.00% 20.00%              
Carrying Value   $ 1,678 $ 1,678   1,678          
Unconsolidated Joint Venture Multi-Family Properties [Member] | Liberty Landing [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   850 850              
Company's Effective Ownership %   50.00% 50.00%              
Carrying Value   $ 337 $ 337   337          
Unconsolidated Joint Venture Multi-Family Properties [Member] | Hillsborough 206 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   160,000 160,000              
Company's Effective Ownership %   50.00% 50.00%              
Carrying Value   $ 1,962 $ 1,962   1,962          
Unconsolidated Joint Venture Office Buildings [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   200,000 200,000              
Unconsolidated Joint Venture Office Buildings [Member] | Red Bank [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Percentage of interest sold 50.00%                  
Unconsolidated Joint Venture Office Buildings [Member] | 12 Vreeland Road [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   139,750 139,750              
Company's Effective Ownership %   50.00% 50.00%              
Carrying Value   $ 4,196 $ 4,196   3,846          
Balance   $ 5,008 $ 5,008              
Property Debt, Maturity Date     Jul. 01, 2023              
Property Debt, Interest Rate   2.87% 2.87%              
Unconsolidated Joint Venture Office Buildings [Member] | Offices At Crystal Lake [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   106,345 106,345              
Company's Effective Ownership %   31.25% 31.25%              
Carrying Value   $ 3,668 $ 3,668   3,521          
Balance   $ 2,733 $ 2,733              
Property Debt, Maturity Date     Nov. 01, 2023              
Property Debt, Interest Rate   4.76% 4.76%              
Unconsolidated Joint Venture Other Property [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Carrying Value   $ 194,779 $ 194,779   209,091          
Balance   $ 793,404 $ 793,404              
Unconsolidated Joint Venture Other Property [Member] | Riverwalk Retail [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Rentable Square Feet (sf) | ft²   30,745 30,745              
Company's Effective Ownership %   20.00% 20.00%         80.00%    
Carrying Value         1,467          
Unconsolidated Joint Venture Other Property [Member] | Hyatt Regency Hotel Jersey City [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units | item   351 351              
Company's Effective Ownership %   50.00% 50.00%              
Carrying Value                
Balance   $ 100,000 $ 100,000              
Property Debt, Maturity Date     Oct. 01, 2026              
Property Debt, Interest Rate   3.668% 3.668%              
Unconsolidated Joint Venture Other Property [Member] | Other [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Carrying Value   $ 100 $ 100   $ 729