Commitments And Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2009	Jul. 05, 2016	Sep. 09, 2015	Mar. 11, 2015	Sep. 18, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 12.3
Property insurance program per occurrence limits	1,000.0
Per occurrence limit for NBCR Coverage	1,000.0
Value of program trigger	$ 120.0
Coinsurance of program trigger	16.00%
Deductible in insurance as a percentage of the value of the affected property, San Francisco and Los Angeles	3.00%
Per occurrence limit of the earthquake insurance which covers San Francisco and Los Angeles regions	$ 170.0
Annual aggregate limit of the earthquake insurance which covers San Francisco and Los Angeles regions	170.0
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco and Los Angeles	20.0
Earthquake Coverage Included In Builders Risk Policy For Below Grade improvements for Salesforce Tower	60.0
Operating partnership guarantee to cover liabilities of IXP	20.0
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	41.7
Property insurance program per occurrence limits	1,625.0
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	$ 28.0						$ 45.2
Bankruptcy Claims, Amount of Claims Settled			$ 1.4	$ 3.6	$ 4.5	$ 7.7
767 Fifth Partners LLC [Member]
Commitments And Contingencies [Line Items]
Ownership Percentage by Parent	60.00%