Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Dec. 31, 2012		Jun. 30, 2012	Dec. 31, 2012		Dec. 31, 2010	Dec. 31, 2011
Mortgages Loans Payable And Other Obligations [Line Items]
Mortgages, loans payable and other obligations	$ 757,495			$ 757,495			$ 739,448
Loss from early extinguishment of debt	(545)		(4,415)	(4,960)		(3,752)
2200 Renaissance Boulevard [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				2200 Renaissance Boulevard (b)	[1]
Lender				Wachovia CMBS	[1]
Effective Rate	5.888%	[1],[2]		5.888%	[1],[2]
Mortgages, loans payable and other obligations							16,171	[1]
Soundview Plaza [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				Soundview Plaza (c)	[3]
Lender				Morgan Stanley Mortgage Capital	[3]
Effective Rate	6.015%	[2],[3]		6.015%	[2],[3]
Mortgages, loans payable and other obligations							15,531	[3]
One Grande Commons [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				One Grande Commons (d)	[4]
Lender				Capital One Bank	[4]
LIBOR				LIBOR+2.00	[2],[4]
Spread over LIBOR	0.02%	[2],[4]		0.02%	[2],[4]
Mortgages, loans payable and other obligations							11,000	[4]
581 Main Street [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				581 Main Street (e)	[5]
Lender				Valley National Bank	[5]
Effective Rate	6.935%	[2],[5]		6.935%	[2],[5]
Mortgages, loans payable and other obligations							16,338	[5]
Loss from early extinguishment of debt				500
Port Imperial South [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				Port Imperial South (h)	[6]
Lender				Wells Fargo Bank N.A.	[6]
LIBOR				LIBOR+2.75	[2],[6]
Spread over LIBOR	0.0275%	[2],[6]		0.0275%	[2],[6]
Mortgages, loans payable and other obligations	42,168	[6]		42,168	[6]
Loan maturity date				Mar. 23, 2013	[6]
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%	[2]		5.534%	[2]
Mortgages, loans payable and other obligations	4,305			4,305			4,479
Loan maturity date				May 01, 2013
Port Imperial South 4/5 [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				Port Imperial South 4/5 (h)	[6]
Lender				Wells Fargo Bank N.A.	[6]
LIBOR				LIBOR+3.50	[2],[6]
Spread over LIBOR	0.035%	[2],[6]		0.035%	[2],[6]
Mortgages, loans payable and other obligations	34,889	[6]		34,889	[6]
Loan maturity date				Sep. 30, 2013	[6]
6305 Ivy Lane [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				6305 Ivy Lane
Lender				John Hancock Life Insurance Co.
Effective Rate	5.525%	[2]		5.525%	[2]
Mortgages, loans payable and other obligations	5,984			5,984			6,245
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	10,231			10,231			10,781
Loan maturity date				May 01, 2014
6301 Ivy Lane [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				6301 Ivy Lane
Lender				John Hancock Life Insurance Co.
Effective Rate	5.52%	[2]		5.52%	[2]
Mortgages, loans payable and other obligations	5,667			5,667			5,899
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	18,746			18,746			19,051
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	63,126			63,126			62,127
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	14,485			14,485			14,438
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	16,251			16,251			15,908
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	38,274			38,274			37,769
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	12,507			12,507			12,056
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	12,275			12,275			11,844
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%	[2]		8.39%	[2]
Mortgages, loans payable and other obligations	3,878			3,878			3,886
Loan maturity date				May 11, 2016
Various [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				Various (f)	[7]
Lender				Prudential Insurance	[7]
Effective Rate	6.332%	[2],[7]		6.332%	[2],[7]
Mortgages, loans payable and other obligations	149,281	[7]		149,281	[7]		150,000	[7]
Loan maturity date				Jan. 15, 2017	[7]
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	30,395			30,395			31,002
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	228,481			228,481			231,603
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 (h)	[6]
Lender				The Provident Bank	[6]
Effective Rate	4.375%	[2],[6]		4.375%	[2],[6]
Mortgages, loans payable and other obligations	3,945	[6]		3,945	[6]
Loan maturity date				Feb. 01, 2019	[6]
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	19,025			19,025			19,241
Loan maturity date				Feb. 01, 2019
One River Center [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name				One River Center (g)	[8]
Lender				Guardian Life Insurance Co.	[8]
Effective Rate	7.311%	[2],[8]		7.311%	[2],[8]
Mortgages, loans payable and other obligations	$ 43,582	[8]		$ 43,582	[8]		$ 44,079	[8]
Loan maturity date				Feb. 01, 2019	[8]
Number of properties used to collateralized mortgage				3

[1] On March 28, 2012, the Company transferred the deed for 2200 Renaissance Boulevard to the lender in satisfaction of its obligations. See Note 7: Discontinued Operations.

[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] On September 4, 2012, the Company repaid this mortgage loan at par, using borrowings under the Company’s unsecured revolving credit facility.

[4] On November 21, 2012, the Company repaid this mortgage loan at par, using proceeds from the sale of senior unsecured notes on November 20, 2012.

[5] On November 20, 2012, the Company repaid this mortgage loan, including a prepayment premium, using proceeds from the sale of senior unsecured notes on November 20, 2012. In connection with this payoff, the Company recorded approximately $0.5 million as a loss from early extinguishment of debt.

[6] Mortgages assumed in connection with the Roseland Transaction. See Note 3: Roseland Transaction.

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

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