Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013		Jun. 30, 2013		Jul. 15, 2013	Dec. 31, 2012
Mortgages Loans Payable And Other Obligations [Line Items]
Spread over LIBOR					1.25%
Mortgages, loans payable and other obligations	$ 753,054		$ 753,054			$ 757,495
Loss from early extinguishment of debt	703		703
51 Imclone [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name			51 Imclone (b)	[1]
Lender			Wachovia CMBS	[1]
Effective Rate	8.39%	[1],[2]	8.39%	[1],[2]
Mortgages, loans payable and other obligations		[1]		[1]		3,878	[1]
9200 Edmonston Road [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name			9200 Edmonston Road (c)	[3]
Lender			Principal Commercial Funding L.L.C.	[3]
Effective Rate	5.534%	[2],[3]	5.534%	[2],[3]
Mortgages, loans payable and other obligations	4,243	[3]	4,243	[3]		4,305	[3]
Loan maturity date			May 01, 2013	[3]
Percentage of leased property occupied	100.00%		100.00%
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	[2]
Spread over LIBOR	2.75%	[2]	2.75%	[2]
Mortgages, loans payable and other obligations	42,500		42,500			42,168
Loan maturity date			Aug. 20, 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	[2]
Spread over LIBOR	3.50%	[2]	3.50%	[2]
Mortgages, loans payable and other obligations	36,355		36,355			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%	[2]	5.525%	[2]
Mortgages, loans payable and other obligations	5,876		5,876			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%	[2]	6.004%	[2]
Mortgages, loans payable and other obligations	9,995		9,995			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%	[2]	5.52%	[2]
Mortgages, loans payable and other obligations	5,572		5,572			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%	[2]	6.348%	[2]
Mortgages, loans payable and other obligations	18,583		18,583			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%	[2]	10.22%	[2]
Mortgages, loans payable and other obligations	63,665		63,665			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%	[2]	10.19%	[2]
Mortgages, loans payable and other obligations	14,511		14,511			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%	[2]	12.44%	[2]
Mortgages, loans payable and other obligations	16,438		16,438			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%	[2]	9.55%	[2]
Mortgages, loans payable and other obligations	38,536		38,536			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%	[2]	12.83%	[2]
Mortgages, loans payable and other obligations	12,751		12,751			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%	[2]	13.42%	[2]
Mortgages, loans payable and other obligations	12,513		12,513			12,275
Loan maturity date			May 11, 2016
Various [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name			Various (d)	[4]
Lender			Prudential Insurance	[4]
Effective Rate	6.332%	[2],[4]	6.332%	[2],[4]
Mortgages, loans payable and other obligations	148,393	[4]	148,393	[4]		149,281	[4]
Loan maturity date			Jan. 15, 2017	[4]
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%	[2]	5.587%	[2]
Mortgages, loans payable and other obligations	30,144		30,144			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%	[2]	6.842%	[2]
Mortgages, loans payable and other obligations	226,838		226,838			228,481
Loan maturity date			Nov. 01, 2018
223 Canoe Brook Road [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name			233 Canoe Brook Road
Lender			The Provident Bank
Effective Rate	4.375%	[2]	4.375%	[2]
Mortgages, loans payable and other obligations	3,911		3,911			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%	[2]	7.311%	[2]
Mortgages, loans payable and other obligations	18,910		18,910			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 (e)	[5]
Lender			Guardian Life Insurance Co.	[5]
Effective Rate	7.311%	[2],[5]	7.311%	[2],[5]
Mortgages, loans payable and other obligations	$ 43,320	[5]	$ 43,320	[5]		$ 43,582	[5]
Loan maturity date			Feb. 01, 2019	[5]
Number of properties used to collateralized mortgage			3

[1] With the sale of the property on May 31, 2013, the mortgage was satisfied by the Company. The Company incurred $0.7 million in costs for the debt satisfaction, which was included in discontinued operations: loss from early retirement of debt for the three and six months ended June 30, 2013.

[2] 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.

[3] The lease with the tenant occupying 100 percent of the building expired on May 1, 2013 and the tenant continues to occupy the building on a month-to-month basis. The mortgage loan matured on May 1, 2013 and was not repaid. The Company received a notice of default from the lender on July 17, 2013. The Company has requested a modification of the loan terms and is also in discussions regarding a deed-in-lieu of foreclosure with the lender.

[4] Mortgage is collateralized by seven properties. The Operating Partnership has agreed, subject to certain conditions, to guarantee repayment of a portion of the loan.

[5] Mortgage is collateralized by the three properties comprising One River Center