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Commitments And Contingencies (Details) | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2020 USD ($) ft² | Dec. 31, 2009 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 10, 2014 USD ($)
Commitments And Contingencies [Line Items] |  |  |  |  |
Letter of credit and performance obligations | $ 21,700,000 |  |  |  |
Notes Receivable, Related Parties | 78,800,000 |  | $ 80,000,000 |  |
Property insurance program per occurrence limits | 1,000,000,000.0 |  |  |  |
Per occurrence limit for NBCR Coverage | 1,000,000,000.0 |  |  |  |
Value of program trigger | $ 200,000,000 |  |  |  |
Coinsurance of program trigger | 20.00% |  |  |  |
Program trigger deductible | 20.00% |  |  |  |
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 | $ 240,000,000 |  |  |  |
Annual aggregate limit of the earthquake insurance which covers San Francisco and Los Angeles regions | 240,000,000 |  |  |  |
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco and Los Angeles | 20,000,000 |  |  |  |
767 Venture, LLC [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Maximum funding obligation | 57,100,000 |  |  |  |
Property insurance program per occurrence limits | 1,625,000,000 |  |  |  |
7750 Wisconsin Avenue [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Liabilities for Contingent Guarantees | 0 |  |  |  |
Lehman [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Bankruptcy claim, amount filed by general creditor |  | $ 45,300,000 |  |  |
Bankruptcy claim amount allowed by court to creditor |  |  |  |  | $ 45,200,000
Bankruptcy Claims, Amount of Claims Settled |  |  |  | $ 18,000,000.0 |
Bankruptcy remaining claim amount allowed by court to creditor | 27,200,000 |  |  |  |
6595 Springfield Center Drive [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Liabilities for Contingent Guarantees | $ 0 |  |  |  |
325 Main Street |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Net Rentable Area (in sf) | ft² | 115,000 |  |  |  |
601 Lexington Avenue |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Coverage For Acts Of Terrorism Under TRIA Covered in Excess of Amount Covered by IXP | $ 250,000,000 |  |  |  |
Boston Properties Limited Partnership |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Notes Receivable, Related Parties | 78,800,000 |  | $ 80,000,000 |  |
Operating partnership guarantee to cover liabilities of IXP | $ 20,000,000.0 |  |  |  |
Future Residential Building [Member] | 325 Main Street |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Net Rentable Area (in sf) | ft² | 200,000 |  |  |  |
Affordable Housing requirement | 25.00% |  |  |  |
Future Office Building [Member] | 325 Main Street |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Net Rentable Area (in sf) | ft² | 420,000 |  |  |  |
Future Retail Building [Member] | 325 Main Street |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Net Rentable Area (in sf) | ft² | 41,000 |  |  |  |
Home Ownership Units [Member] | Future Residential Building [Member] | 325 Main Street |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Affordable Housing requirement | 20.00% |  |  |  |
Maximum [Member] | 7750 Wisconsin Avenue [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Notes Receivable, Related Parties | $ 15,000,000.0 |  |  |  |
Minimum [Member] | 7750 Wisconsin Avenue [Member] |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |
Notes Receivable, Related Parties | $ 0 |  |  |  |

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