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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 |  |  |  |  |

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