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