Commitments And Contingencies (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2009	Dec. 31, 2015	Mar. 11, 2015	Dec. 31, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 22.5
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	3.00%
Per occurrence limit of the earthquake insurance which covers San Francisco region	$ 170.0
Annual aggregate limit of the earthquake insurance which covers San Francisco region	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
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	$ 16.2
Ownership Percentage by the Company	60.00%
Property insurance program per occurrence limits	$ 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			$ 8.1	$ 4.5	$ 7.7
Bankruptcy remaining claim amount allowed by court to creditor	29.4
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
Boston Properties Limited Partnership
Commitments And Contingencies [Line Items]
Operating partnership guarantee to cover liabilities of IXP	$ 20.0