Commitments and Contingencies (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011
Letter of credit and performance obligations	$ 16,300,000
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
Seven Six Seven Venture, LLC [Member]
Maximum funding obligation	21,300,000
Coverage for acts of terrorism certified under TRIA in excess of amount provided by NYXP, 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 provided by NYXP, LLC, as a direct insurer	250,000,000
One Two Five West Fifty-Fifth Street Venture, LLC [Member]
Maximum funding obligation	21,300,000
Maximum exposure as of period end	4,500,000
Cash deposit into the escrow account	10,000,000
Escrow account remaining funding obligation	11,300,000
One Freedom Square [Member]
Guarantee obligation related to tenant re-leasing costs	$ 7,900,000