Commitments And Contingencies (Details) - USD ($) $ in Millions	2 Months Ended	4 Months Ended	6 Months Ended	12 Months Ended
	Feb. 28, 2015	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2009	Mar. 11, 2015	Dec. 31, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations		$ 23.5	$ 23.5
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 Salesforce Tower			60.0
Operating partnership guarantee to cover liabilities of IXP		20.0	20.0
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation		29.5	29.5
Property insurance program per occurrence limits		1,625.0	1,625.0
Lehman [Member]
Commitments And Contingencies [Line Items]
Bankruptcy claim, amount filed by general creditor				$ 45.3
Bankruptcy claim amount allowed by court to creditor							$ 45.2
Bankruptcy Claims, Amount of Claims Settled					$ 4.5	$ 7.7
Bankruptcy remaining claim amount allowed by court to creditor		$ 33.0	33.0
200 Clarendon Street [Member]
Commitments And Contingencies [Line Items]
Guarantee Obligation Related To Tenant Re-Leasing Costs			25.3
Fountain Square [Member]
Commitments And Contingencies [Line Items]
Guarantee Obligation Related To Tenant Re-Leasing Costs			0.7
601 Lexington Avenue [Member]
Commitments And Contingencies [Line Items]
Coverage For Acts Of Terrorism Under TRIA Covered in Excess of Amount Covered by IXP			$ 250.0