Investments In Unconsolidated Joint Ventures (Summary Of Unconsolidated Joint Ventures) (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Apr. 29, 2021 USD ($)	Mar. 31, 2021 USD ($) ft² item	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Schedule of Equity Method Investments [Line Items]
Carrying Value		$ 159,971		$ 162,382
Purchase price of property		$ 16,978	$ 63,004
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%
PI North - Riverwalk C [Member] | Construction Loan [Member]
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity		$ 112,000
Percent of principal loan outstanding		10.00%
PI North - Land [Member]
Schedule of Equity Method Investments [Line Items]
Number of Apartment Units | item		771
Residual ownership interest		20.00%
12 Vreeland Road [Member]
Schedule of Equity Method Investments [Line Items]
Property impairments on continuing operations				2,600
12 Vreeland Road [Member] | Subsequent Event [Member]
Schedule of Equity Method Investments [Line Items]
Gain on sale	$ 2,000
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
Balance		$ 6,067
Property Debt, Interest Rate, Spread Over LIBOR		0.015%
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
Property Debt, Interest Rate, Spread Over LIBOR		0.015%
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
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		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		$ 3,116		3,347
Balance		$ 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
Company's Effective Ownership %		22.50%
Carrying Value		$ 6,472		6,667
Balance		$ 82,000
Property Debt, Maturity Date		Nov. 10, 2026
Property Debt, Interest Rate		3.21%
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		$ 37,201		36,992
Balance		$ 86,116
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		$ 604		681
Balance		$ 30,192
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		$ 33,962		34,026
Balance		$ 94,693
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		$ 70,817		72,752
Balance		$ 192,000
Property Debt, Maturity Date		Aug. 01, 2029
Property Debt, Interest Rate		5.197%
Guaranteed amount		$ 22,000
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		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
Company's Effective Ownership %		50.00%
Carrying Value		$ 337		337
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] | 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		1,811
Balance		$ 4,154
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		$ 3,626		3,744
Balance		$ 2,328
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		$ 159,971		162,382
Balance		$ 652,250
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
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		$ 347