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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 15, 2020
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Interest capitalized | $ 53,881,000 | $ 54,911,000 | $ 65,766,000 |
Salaries And Related Costs Capitalized | 12,900,000 | 10,400,000 | 12,500,000 |
Cash FDIC Insured Limit | 250,000 |  |  |
Gains (losses) from investments in securities | 5,261,000 | 6,417,000 | (1,865,000) |
Internal Leasing Salaries And Related Costs Capitalized |  |  | 5,400,000 |
Straight Line Rent Adjustments | 104,900,000 | 58,400,000 | 51,900,000 |
Above and below market rent adjustments, net | 6,500,000 | 20,900,000 | 23,800,000 |
Separate Unrestricted Cash For Deferred Compensation Plan. | 39,500,000 | 36,700,000 |  |
Adoption of ASU 2016-13 and 2018-19 | (509,653,000) | (760,523,000) |  |
Adoption of ASU 2016-13 and 2018-19 | 616,596,000 | 600,860,000 |  |
Distributions Payable, Amount Per Unit |  |  |  | $ 0.98
Boston Properties Limited Partnership |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Interest capitalized | 53,881,000 | 54,911,000 | 65,766,000 |
Gains (losses) from investments in securities | 5,261,000 | 6,417,000 | $ (1,865,000) |
Adoption of ASU 2016-13 and 2018-19 | 4,554,639,000 | 3,380,175,000 |  |
Adoption of ASU 2016-13 and 2018-19 | 1,643,024,000 | $ 2,468,753,000 |  |
Distributions Payable, Amount Per Unit |  |  |  | $ 0.98
Boston Properties Limited Partnership | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Adoption of ASU 2016-13 and 2018-19 | 1,500,000 |  |  |
Dividends In Excess Of Earnings [Member] | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Adoption of ASU 2016-13 and 2018-19 | 1,500,000 |  |  |
Noncontrolling Interests [Member] | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Adoption of ASU 2016-13 and 2018-19 | 200,000 |  |  |
Noncontrolling Interests [Member] | Boston Properties Limited Partnership | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Adoption of ASU 2016-13 and 2018-19 | $ 200,000 |  |  |

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