Commitments And Contingencies (Details) - USD ($) $ in Millions	2 Months Ended	10 Months Ended	12 Months Ended
	Feb. 28, 2015	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2009	Sep. 09, 2015	Mar. 11, 2015	Sep. 18, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations		$ 22.8	$ 22.8
Property insurance program per occurrence limits		1,000.0	1,000.0
Per occurrence limit for NBCR Coverage			1,000.0
Value of program trigger		100.0	$ 100.0
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	$ 120.0	170.0
Annual aggregate limit of the earthquake insurance which covers San Francisco region	$ 120.0	170.0
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco			$ 20.0
Earthquake Coverage Included In Builders Risk Policy For Below Grade improvements for Transbay Tower			60.0
Operating partnership guarantee to cover liabilities of IXP		20.0	20.0
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Property insurance program per occurrence limits		1,625.0	1,625.0
Fountain Square
Commitments And Contingencies [Line Items]
Guarantee Obligation Related To Tenant Re-Leasing Costs			0.7
601 Lexington Avenue
Commitments And Contingencies [Line Items]
Coverage For Acts Of Terrorism Under TRIA Covered in Excess of Amount Covered by IXP			250.0
Lehman [Member]
Commitments And Contingencies [Line Items]
Bankruptcy claim, amount filed by general creditor				$ 45.3
Bankruptcy claim amount allowed by court to creditor		$ 29.4	$ 29.4					$ 45.2
Bankruptcy Claims, Amount of Claims Settled					$ 3.6	$ 4.5	$ 7.7