Mortgages, Loans Payable And Other Obligations (Summary Of Mortgages, Loans Payable And Other Obligations) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Mortgages Loans Payable And Other Obligations [Line Items]
Mortgages, loans payable and other obligations	$ 704,940		$ 739,448
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]
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]
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]
Effective Rate	2.00%	[2]
Mortgages, loans payable and other obligations	11,000	[4]	11,000	[4]
Loan maturity date	Dec. 31, 2012	[4]
Number of extension options	2
Mortgage loan, extension period	1 year
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]
Mortgages, loans payable and other obligations	4,349		4,479
Loan maturity date	May 01, 2013
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]
Mortgages, loans payable and other obligations	6,064		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]
Mortgages, loans payable and other obligations	10,396		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]
Mortgages, loans payable and other obligations	5,739		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]
Mortgages, loans payable and other obligations	18,826		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]
Mortgages, loans payable and other obligations	62,867		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]
Mortgages, loans payable and other obligations	14,473		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]
Mortgages, loans payable and other obligations	16,161		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]
Mortgages, loans payable and other obligations	38,148		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]
Mortgages, loans payable and other obligations	12,391		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]
Mortgages, loans payable and other obligations	12,162		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]
Mortgages, loans payable and other obligations	3,880		3,886
Loan maturity date	May 11, 2016
Various [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name	Various (e)	[5]
Lender	Prudential Insurance	[5]
Effective Rate	6.332%	[2],[5]
Mortgages, loans payable and other obligations	149,715	[5]	150,000	[5]
Loan maturity date	Jan. 15, 2017	[5]
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]
Mortgages, loans payable and other obligations	30,586		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]
Mortgages, loans payable and other obligations	229,281		231,603
Loan maturity date	Nov. 01, 2018
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]
Mortgages, loans payable and other obligations	19,080		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 (f)	[6]
Lender	Guardian Life Insurance Co.	[6]
Effective Rate	7.311%	[2],[6]
Mortgages, loans payable and other obligations	43,710	[6]	44,079	[6]
Loan maturity date	Feb. 01, 2019	[6]
Number of properties used to collateralized mortgage	3
581 Main Street [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Property Name	581 Main Street (g)	[7]
Lender	Valley National Bank	[7]
Effective Rate	6.935%	[2],[7],[8]
Mortgages, loans payable and other obligations	$ 16,112	[7]	$ 16,338	[7]
Loan maturity date	Jul. 01, 2034	[7]
Basis points of the interest rate at the reset period	2.25%
Treasury yield period	10 years
Period prior to reset date that interest rate will be reset	45 days
Minimum interest rate for the loan after the reset period	6.875%
Coupon Interest Rate Reset One [Member] | 581 Main Street [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Interest rate will be reset after the end of period	10 years
Coupon Interest Rate Reset Two [Member] | 581 Main Street [Member]
Mortgages Loans Payable And Other Obligations [Line Items]
Interest rate will be reset after the end of period	20 years

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

[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] The mortgage loan has two one-year extension options, subject to certain conditions and the payment of a fee.

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

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

[7] The Operating Partnership has agreed, subject to certain conditions, to guarantee repayment of a portion of the loan.

[8] The coupon interest rate will be reset at the end of year 10 (2019) and year 20 (2029) at 225 basis points over the 10-year treasury yield 45 days prior to the reset dates with a minimum rate of 6.875 percent.