Quarterly report pursuant to Section 13 or 15(d)

Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details)

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Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details)
6 Months Ended
Mar. 29, 2018
USD ($)
Mar. 01, 2018
USD ($)
Jan. 08, 2018
USD ($)
Jun. 30, 2018
USD ($)
property
item
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]            
Principal balance outstanding       $ 2,646,437,000   $ 2,809,568,000
Borrowings from revolving credit facility       371,000,000 $ 334,000,000  
Payment for borrowings       338,000,000 $ 521,000,000  
Secured Debt [Member]            
Debt Instrument [Line Items]            
Principal balance outstanding       1,227,517,000   1,426,111,000
Unamortized deferred financing costs       (6,998,000)   (7,976,000)
Total mortgages, loans payable and other obligations, net       $ 1,220,519,000   1,418,135,000
Secured Debt [Member] | Harborside Plaza 5 [Member]            
Debt Instrument [Line Items]            
Property Name       Harborside Plaza 5    
Lender       The Northwestern Mutual Life Insurance Co. & New York Life Insurance Co.    
Effective rate       6.84%    
Principal balance outstanding         209,257,000
Payment for borrowings     $ 8,400,000      
Secured Debt [Member] | 23 Main Street [Member]            
Debt Instrument [Line Items]            
Property Name       23 Main Street    
Lender       Berkadia CMBS    
Effective rate       5.59%    
Principal balance outstanding         27,090,000
Payment for borrowings   $ 100,000        
Secured Debt [Member] | One River Center [Member]            
Debt Instrument [Line Items]            
Property Name       One River Center    
Lender       Guardian Life Insurance Co.    
Effective rate       7.31%    
Principal balance outstanding         40,485,000
Number of properties used to collateralized mortgage | property       3    
Payment for borrowings $ 1,800,000          
Secured Debt [Member] | Park Square [Member]            
Debt Instrument [Line Items]            
Property Name       Park Square    
Lender       Wells Fargo Bank N.A.    
LIBOR       LIBOR+1.87    
Spread over LIBOR       1.87%    
Principal balance outstanding       $ 25,867,000   26,567,000
Loan maturity date       Apr. 10, 2019    
Secured Debt [Member] | 250 Johnson Road [Member]            
Debt Instrument [Line Items]            
Property Name       250 Johnson    
Lender       M&T Bank    
LIBOR       LIBOR+2.35    
Spread over LIBOR       2.35%    
Principal balance outstanding       $ 39,918,000   32,491,000
Loan maturity date       May 20, 2019    
Secured Debt [Member] | 250 Johnson Road [Member] | Construction Loan [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity       $ 42,000,000    
Loan extension period       1 year    
Extension fee       0.25%    
Secured Debt [Member] | Portside 5/6 [Member]            
Debt Instrument [Line Items]            
Property Name       Portside 5/6    
Lender       Citizens Bank    
LIBOR       LIBOR+2.50    
Spread over LIBOR       2.50%    
Principal balance outstanding       $ 67,088,000   45,778,000
Loan maturity date       Sep. 29, 2019    
Secured Debt [Member] | Portside 5/6 [Member] | Construction Loan [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity       $ 73,000,000    
Number of extension options | item       2    
Loan extension period       1 year    
Extension fee       0.15%    
Secured Debt [Member] | Port Imperial 4/5 Hotel [Member]            
Debt Instrument [Line Items]            
Property Name       Port Imperial 4/5 Hotel    
Lender       Fifth Third Bank & Santander    
LIBOR       LIBOR+4.50    
Spread over LIBOR       4.50%    
Principal balance outstanding       $ 65,598,000   43,674,000
Loan maturity date       Oct. 06, 2019    
Secured Debt [Member] | Port Imperial 4/5 Hotel [Member] | Construction Loan [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity       $ 94,000,000    
Number of extension options | item       2    
Loan extension period       1 year    
Extension fee       0.20%    
Secured Debt [Member] | Port Imperial South 11 [Member]            
Debt Instrument [Line Items]            
Property Name       Port Imperial South 11    
Lender       JPMorgan Chase    
LIBOR       LIBOR+2.35    
Spread over LIBOR       2.35%    
Principal balance outstanding       $ 60,107,000   46,113,000
Loan maturity date       Nov. 24, 2019    
Secured Debt [Member] | Port Imperial South 11 [Member] | Construction Loan [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity       $ 78,000,000    
Number of extension options | item       2    
Loan extension period       1 year    
Extension fee       0.15%    
Secured Debt [Member] | Worcester [Member]            
Debt Instrument [Line Items]            
Property Name       Worcester    
Lender       Citizens Bank    
LIBOR       LIBOR+2.50    
Spread over LIBOR       2.50%    
Principal balance outstanding       $ 52,913,000   37,821,000
Loan maturity date       Dec. 10, 2019    
Secured Debt [Member] | Worcester [Member] | Construction Loan [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity       $ 58,000,000    
Number of extension options | item       2    
Loan extension period       1 year    
Extension fee       0.15%    
Secured Debt [Member] | Monaco [Member]            
Debt Instrument [Line Items]            
Property Name       Monaco    
Lender       The Northwestern Mutual Life Insurance Co.    
Effective rate       3.15%    
Principal balance outstanding       $ 169,178,000   169,987,000
Loan maturity date       Feb. 01, 2021    
Adjustment for unamortized debt discount       $ 4,200,000    
Secured Debt [Member] | Port Imperial South 4/5 Retail [Member]            
Debt Instrument [Line Items]            
Property Name       Port Imperial South 4/5 Retail    
Lender       American General Life & A/G PC    
Effective rate       4.56%    
Principal balance outstanding       $ 4,000,000   4,000,000
Loan maturity date       Dec. 01, 2021    
Secured Debt [Member] | Portside 7 [Member]            
Debt Instrument [Line Items]            
Property Name       Portside 7    
Lender       CBRE Capital Markets/FreddieMac    
Effective rate       3.57%    
Principal balance outstanding       $ 58,998,000   58,998,000
Loan maturity date       Aug. 01, 2023    
Secured Debt [Member] | Alterra I & II [Member]            
Debt Instrument [Line Items]            
Property Name       Alterra I & II    
Lender       Capital One/FreddieMac    
Effective rate       3.85%    
Principal balance outstanding       $ 100,000,000   100,000,000
Loan maturity date       Feb. 01, 2024    
Secured Debt [Member] | The Chase At Overlook Ridge [Member]            
Debt Instrument [Line Items]            
Property Name       The Chase at Overlook Ridge    
Lender       New York Community Bank    
Effective rate       3.74%    
Principal balance outstanding       $ 135,750,000   135,750,000
Loan maturity date       Jan. 01, 2025    
Secured Debt [Member] | 101 Hudson Street [Member]            
Debt Instrument [Line Items]            
Property Name       101 Hudson    
Lender       Wells Fargo CMBS    
Effective rate       3.20%    
Principal balance outstanding       $ 250,000,000   250,000,000
Loan maturity date       Oct. 11, 2026    
Secured Debt [Member] | Short Hills Portfolio [Member]            
Debt Instrument [Line Items]            
Property Name       Short Hills Portfolio    
Lender       Wells Fargo CMBS    
Effective rate       4.15%    
Principal balance outstanding       $ 124,500,000   124,500,000
Loan maturity date       Apr. 01, 2027    
Secured Debt [Member] | 150 Main St [Member]            
Debt Instrument [Line Items]            
Property Name       150 Main St.    
Lender       Natixis Real Estate Capital LLC    
Effective rate       4.48%    
Principal balance outstanding       $ 41,000,000   41,000,000
Loan maturity date       Aug. 05, 2027    
Secured Debt [Member] | Port Imperial 4/5 Garage Development [Member]            
Debt Instrument [Line Items]            
Property Name       Port Imperial South 4/5 Garage    
Lender       American General Life & A/G PC    
Effective rate       4.85%    
Principal balance outstanding       $ 32,600,000   $ 32,600,000
Loan maturity date       Dec. 01, 2029