Commitments And Contingencies (Details) (USD $)	0 Months Ended		9 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	Sep. 30, 2011
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations			$ 16,100,000
Property insurance program per occurrence limits			1,000,000,000
Per occurrence limit for NBCR Coverage			1,000,000,000
Value of program trigger			100,000,000
Coinsurance of program trigger			15.00%
Deductible in insurance as a percentage of the value of the affected property, San Francisco			5.00%
Per occurrence limit of the earthquake insurance which covers San Francisco region			120,000,000
Annual aggregate limit of the earthquake insurance which covers San Francisco region			120,000,000
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco			20,000,000
Maturity date	Feb. 15, 2037	Nov. 15, 2018
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation			10,600,000
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by IXP, LLC, as a direct insurer			1,375,000,000
Property insurance program per occurrence limits			1,625,000,000
Coverage for acts of terrorism certified under TRIA in excess			250,000,000
125 West 55th Street Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation			21,300,000
Maximum exposure as of period end			3,200,000
Cash deposit into the escrow account			10,000,000
Escrow account remaining funding obligation			11,300,000
One Freedom Square [Member]
Commitments And Contingencies [Line Items]
Guarantee obligation related to tenant re-leasing costs			7,900,000
Maturity date			Jun. 30, 2012
601 Lexington Avenue [Member]
Commitments And Contingencies [Line Items]
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by IXP, LLC, as a direct insurer			$ 250,000,000