Investments In Unconsolidated Joint Ventures (Summary Of Unconsolidated Joint Ventures) (Details)
 9 Months Ended 12 Months Ended
Dec. 17, 2020
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Sep. 18, 2020
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Sep. 30, 2020
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Dec. 31, 2020
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ft²
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Dec. 31, 2019
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Dec. 31, 2018
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Mar. 12, 2020
Jan. 30, 2019
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Schedule of Equity Method Investments [Line Items]                
Number of Apartment Units | item       326 208      
Carrying Value       $ 162,382,000 $ 209,091,000      
Purchase price of property       138,688,000 88,240,000 $ 113,523,000    
Property impairments on continuing operations     $ 36,600,000 $ 36,582,000        
Minimum [Member]                
Schedule of Equity Method Investments [Line Items]                
Company's Effective Ownership %       20.00%        
Maximum [Member]                
Schedule of Equity Method Investments [Line Items]                
Company's Effective Ownership %       85.00%        
Metropolitan And Lofts At 40 Park [Member]                
Schedule of Equity Method Investments [Line Items]                
Rentable Square Feet (sf) | ft²       50,973        
Crystal House [Member]                
Schedule of Equity Method Investments [Line Items]                
Gain on sale       $ 35,100,000        
PI North - Riverwalk C [Member] | Construction Loan [Member]                
Schedule of Equity Method Investments [Line Items]                
Maximum borrowing capacity       $ 112,000,000        
Riverpark At Harrison [Member]                
Schedule of Equity Method Investments [Line Items]                
Maximum borrowing capacity               $ 30,192,000
PI North - Land [Member] | Construction Loan [Member]                
Schedule of Equity Method Investments [Line Items]                
Percent of principal loan outstanding       10.00%        
Hillsborough 206 [Member]                
Schedule of Equity Method Investments [Line Items]                
Gain on sale $ 100,000              
Sale price $ 2,100,000              
12 Vreeland Road [Member]                
Schedule of Equity Method Investments [Line Items]                
Property impairments on continuing operations       $ 2,600,000 3,700,000      
The Shops At 40 Park Property [Member] | Metropolitan And Lofts At 40 Park [Member]                
Schedule of Equity Method Investments [Line Items]                
Balance   $ 6,067,000            
Property Debt, Interest Rate, Spread Over LIBOR   1.50%            
Residual ownership interest       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        
Balance   $ 18,200,000            
Property Debt, Interest Rate, Spread Over LIBOR   1.50%            
Indirect ownership interest       50.00%        
Number of stories | item       5        
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   $ 36,500,000            
Property Debt, Interest Rate, Spread Over LIBOR   2.85%            
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       1,786        
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        
Company's Effective Ownership %       25.00%        
Carrying Value       $ 3,347,000 7,257,000      
Balance       $ 60,767,000        
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        
Company's Effective Ownership %       22.50%        
Carrying Value       $ 6,667,000 7,463,000      
Balance       $ 82,000,000        
Property Debt, Maturity Date       Nov. 10, 2026        
Property Debt, Interest Rate       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        
Company's Effective Ownership %       25.00%        
Carrying Value         28,823,000      
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        
Company's Effective Ownership %       40.00%        
Carrying Value       $ 36,992,000 35,527,000      
Balance       $ 75,569,000        
Property Debt, Maturity Date       Dec. 06, 2021        
Property Debt, Interest Rate       2.75%        
Unconsolidated Joint Venture Multi-Family Properties [Member] | Riverpark At Harrison [Member]                
Schedule of Equity Method Investments [Line Items]                
Number of Apartment Units | item       141        
Company's Effective Ownership %       45.00%        
Carrying Value       $ 681,000 1,015,000      
Balance       $ 30,192,000        
Property Debt, Maturity Date       Jul. 01, 2035        
Property Debt, Interest Rate       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        
Company's Effective Ownership %       50.00%        
Carrying Value       $ 34,026,000 35,676,000      
Balance       $ 95,137,000        
Property Debt, Maturity Date       Jul. 01, 2033        
Property Debt, Interest Rate       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        
Company's Effective Ownership %       85.00%        
Carrying Value       $ 72,752,000 79,790,000      
Balance       $ 192,000,000        
Property Debt, Maturity Date       Aug. 01, 2029        
Property Debt, Interest Rate       5.197%        
Guaranteed amount       $ 22,000,000        
Unconsolidated Joint Venture Multi-Family Properties [Member] | PI North - Land [Member]                
Schedule of Equity Method Investments [Line Items]                
Number of Apartment Units | item       771        
Company's Effective Ownership %       20.00%        
Carrying Value       $ 1,678,000 1,678,000      
Unconsolidated Joint Venture Multi-Family Properties [Member] | Liberty Landing [Member]                
Schedule of Equity Method Investments [Line Items]                
Number of Apartment Units | item       850        
Company's Effective Ownership %       50.00%        
Carrying Value       $ 337,000 337,000      
Unconsolidated Joint Venture Multi-Family Properties [Member] | Hillsborough 206 [Member]                
Schedule of Equity Method Investments [Line Items]                
Rentable Square Feet (sf) | ft²       160,000        
Company's Effective Ownership %       50.00%        
Carrying Value         1,962,000      
Unconsolidated Joint Venture Office Buildings [Member]                
Schedule of Equity Method Investments [Line Items]                
Rentable Square Feet (sf) | ft²       200,000        
Unconsolidated Joint Venture Office Buildings [Member] | Crystal House [Member]                
Schedule of Equity Method Investments [Line Items]                
Gain on sale       $ 35,100,000        
Unconsolidated Joint Venture Office Buildings [Member] | 12 Vreeland Road [Member]                
Schedule of Equity Method Investments [Line Items]                
Rentable Square Feet (sf) | ft²       139,750        
Company's Effective Ownership %       50.00%        
Carrying Value       $ 1,811,000 3,846,000      
Balance       $ 4,582,000        
Property Debt, Maturity Date       Jul. 01, 2023        
Property Debt, Interest Rate       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        
Company's Effective Ownership %       31.25%        
Carrying Value       $ 3,744,000 3,521,000      
Balance       $ 2,532,000        
Property Debt, Maturity Date       Nov. 01, 2023        
Property Debt, Interest Rate       4.76%        
Unconsolidated Joint Venture Other Property [Member]                
Schedule of Equity Method Investments [Line Items]                
Carrying Value       $ 162,382,000 209,091,000      
Balance       $ 642,779,000        
Unconsolidated Joint Venture Other Property [Member] | Riverwalk Retail [Member]                
Schedule of Equity Method Investments [Line Items]                
Rentable Square Feet (sf) | ft²       30,745        
Company's Effective Ownership %       20.00%     80.00%  
Carrying Value         1,467,000      
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        
Company's Effective Ownership %       50.00%        
Balance       $ 100,000,000        
Property Debt, Maturity Date       Oct. 01, 2026        
Property Debt, Interest Rate       3.668%        
Unconsolidated Joint Venture Other Property [Member] | Other [Member]                
Schedule of Equity Method Investments [Line Items]                
Carrying Value       $ 347,000 $ 729,000