Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Mortgages Loans Payable And Other Obligations [Line Items]    
Mortgages, loans payable and other obligations $ 757,700 $ 757,495
9200 Edmonston Road [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 9200 Edmonston Road  
Lender Principal Commercial Funding L.L.C.  
Effective Rate 5.534% [1]  
Mortgages, loans payable and other obligations 4,258 4,305
Loan maturity date May 01, 2013  
Port Imperial South [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name Port Imperial South  
Lender Wells Fargo Bank N.A.  
LIBOR LIBOR+2.75 [1]  
Spread over LIBOR 0.0275% [1]  
Mortgages, loans payable and other obligations 42,474 42,168
Loan maturity date Jun. 24, 2013  
Port Imperial South 4/5 [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name Port Imperial South 4/5  
Lender Wells Fargo Bank N.A.  
LIBOR LIBOR+3.50 [1]  
Spread over LIBOR 0.035% [1]  
Mortgages, loans payable and other obligations 35,947 34,889
Loan maturity date Sep. 30, 2013  
6305 Ivy Lane [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 6305 Ivy Lane  
Lender RGA Reinsurance Company  
Effective Rate 5.525% [1]  
Mortgages, loans payable and other obligations 5,939 5,984
Loan maturity date Jan. 01, 2014  
395 West Passaic [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 395 West Passaic  
Lender State Farm Life Insurance Co.  
Effective Rate 6.004% [1]  
Mortgages, loans payable and other obligations 10,131 10,231
Loan maturity date May 01, 2014  
6301 Ivy Lane [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 6301 Ivy Lane  
Lender RGA Reinsurance Company  
Effective Rate 5.52% [1]  
Mortgages, loans payable and other obligations 5,628 5,667
Loan maturity date Jul. 01, 2014  
35 Waterview Boulevard [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 35 Waterview Boulevard  
Lender Wachovia CMBS  
Effective Rate 6.348% [1]  
Mortgages, loans payable and other obligations 18,662 18,746
Loan maturity date Aug. 11, 2014  
6 Becker, 85 Livingston, 75 Livingston & 20 Waterview [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 6 Becker, 85 Livingston, 75 Livingston & 20 Waterview  
Lender Wachovia CMBS  
Effective Rate 10.22% [1]  
Mortgages, loans payable and other obligations 63,392 63,126
Loan maturity date Aug. 11, 2014  
4 Sylvan [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 4 Sylvan  
Lender Wachovia CMBS  
Effective Rate 10.19% [1]  
Mortgages, loans payable and other obligations 14,498 14,485
Loan maturity date Aug. 11, 2014  
10 Independence [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 10 Independence  
Lender Wachovia CMBS  
Effective Rate 12.44% [1]  
Mortgages, loans payable and other obligations 16,343 16,251
Loan maturity date Aug. 11, 2014  
4 Becker [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 4 Becker  
Lender Wachovia CMBS  
Effective Rate 9.55% [1]  
Mortgages, loans payable and other obligations 38,393 38,274
Loan maturity date May 11, 2016  
5 Becker [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 5 Becker  
Lender Wachovia CMBS  
Effective Rate 12.83% [1]  
Mortgages, loans payable and other obligations 12,623 12,507
Loan maturity date May 11, 2016  
210 Clay [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 210 Clay  
Lender Wachovia CMBS  
Effective Rate 13.42% [1]  
Mortgages, loans payable and other obligations 12,392 12,275
Loan maturity date May 11, 2016  
51 Imclone [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 51 Imclone  
Lender Wachovia CMBS  
Effective Rate 8.39% [1]  
Mortgages, loans payable and other obligations 3,876 3,878
Loan maturity date May 11, 2016  
Various [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name Various (b) [2]  
Lender Prudential Insurance [2]  
Effective Rate 6.332% [1],[2]  
Mortgages, loans payable and other obligations 148,840 [2] 149,281 [2]
Loan maturity date Jan. 15, 2017 [2]  
Number of properties used to collateralized mortgage 7  
23 Main Street [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 23 Main Street  
Lender JPMorgan CMBS  
Effective Rate 5.587% [1]  
Mortgages, loans payable and other obligations 30,289 30,395
Loan maturity date Sep. 01, 2018  
Harborside Plaza 5 [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name Harborside Plaza 5  
Lender The Northwestern Mutual Life Insurance Co. & New York Life Insurance Co.  
Effective Rate 6.842% [1]  
Mortgages, loans payable and other obligations 227,666 228,481
Loan maturity date Nov. 01, 2018  
223 Canoe Brook Road [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 223 Canoe Brook Road  
Lender The Provident Bank  
Effective Rate 4.375% [1]  
Mortgages, loans payable and other obligations 3,928 3,945
Loan maturity date Feb. 01, 2019  
100 Walnut Avenue [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name 100 Walnut Avenue  
Lender Guardian Life Insurance Co.  
Effective Rate 7.311% [1]  
Mortgages, loans payable and other obligations 18,968 19,025
Loan maturity date Feb. 01, 2019  
One River Center [Member]
    
Mortgages Loans Payable And Other Obligations [Line Items]    
Property Name One River Center (c) [3]  
Lender Guardian Life Insurance Co. [3]  
Effective Rate 7.311% [1],[3]  
Mortgages, loans payable and other obligations $ 43,453 [3] $ 43,582 [3]
Loan maturity date Feb. 01, 2019 [3]  
Number of properties used to collateralized mortgage 3  
[1] Reflects effective rate of debt, including deferred financing costs, comprised of the cost of terminated treasury lock agreements (if any), debt initiation costs, mark-to-market adjustment of acquired debt and other transaction costs, as applicable.
[2] Mortgage is collateralized by seven properties. The Operating Partnership has agreed, subject to certain conditions, to guarantee repayment of a portion of the loan.
[3] Mortgage is collateralized by the three properties comprising One River Center