Commitments And Contingencies (Details) (USD $)	3 Months Ended					3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 767 Venture, LLC [Member]	Mar. 31, 2012 125 West 55th Street Venture LLC [Member]	Mar. 31, 2010 125 West 55th Street Venture LLC [Member]	Mar. 31, 2012 601 Lexington Avenue [Member]	Mar. 31, 2012 One Freedom Square [Member]
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 16,300,000
Maximum funding obligation		13,500,000	500,000	21,300,000
Guarantee obligation related to tenant re-leasing costs						7,900,000
Cash deposit into the escrow account				10,000,000
Escrow account remaining funding obligation				11,300,000
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by NYIXP, LLC, as a direct insurer		1,375,000,000			250,000,000
Property insurance program per occurrence limits	1,000,000,000	1,625,000,000
Coverage for acts of terrorism certified under TRIA in excess		250,000,000
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
Operating partnership guarantee to cover liabilities of IXP	$ 20,000,000