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Summary Of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items] |
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] | Fair Value of Financial Instruments The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. The table below presents the financial instruments that are being valued for disclosure purposes as well as the Level at which they are categorized as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”) (see “New Accounting Pronouncements Adopted—Fair Value Measurement”).
Financial Instrument | Level
Unsecured senior notes (1) | Level 1
Related party note receivable | Level 3
Notes receivable | Level 3
Mortgage notes payable | Level 3
Unsecured term loan / line of credit | Level 3
_______________ (1) If trading volume for the period is low, the valuation could be categorized as Level 2. Because the Company’s valuations of its financial instruments are based on the above Levels and involve the use of estimates, the actual fair values of its financial instruments may differ materially from those estimates. The following table identifies the range and weighted average discount rate for the significant unobservable inputs for the Company’s Level 3 fair value measured instruments as of December 31, 2020.
Financial Instrument | Level | Range | Weighted Average
Related party note receivable | Level 3 | 3.64% | 3.64%
Notes receivable | Level 3 | 3.60% - 8.00% | 5.87%
Mortgage notes payable | Level 3 | 2.00% - 3.04% | 2.21%
Unsecured term loan / line of credit | Level 3 | 1.04% | 1.04%
In addition, the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not projections of, nor necessarily indicative of, estimated or actual fair values in future reporting periods.
Property, Plant and Equipment | Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows:
Land improvements |  | 25 to 40 years
Buildings and improvements |  | 10 to 40 years
Tenant improvements |  | Shorter of useful life or terms of related lease
Furniture, fixtures, and equipment |  | 3 to 7 years
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense | The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands).
|  | Acquired Above-Market Lease Intangibles |  | Acquired Below-Market Lease Intangibles
2021 |  | $ | 3,019 |  |  | $ | 6,193 |
2022 |  | 354 |  |  | 5,437 |
2023 |  | 183 |  |  | 5,296 |
2024 |  | 135 |  |  | 3,780 |
2025 |  | 135 |  |  | 3,775 |
Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period during which the expenses are incurred (See “Leases” ).
Fair Value, by Balance Sheet Grouping [Table Text Block] |
| December 31, 2020 |  | December 31, 2019
| Carrying Amount |  | Estimated Fair Value |  | Carrying Amount |  | Estimated Fair Value
Related party note receivable, net | $ | 77,552 |  |  | $ | 84,579 |  |  | $ | 80,000 |  |  | $ | 81,931 |
Note receivable, net | 18,729 |  |  | 19,372 |  |  | 15,920 |  |  | 14,978 |
Total | $ | 96,281 |  |  | $ | 103,951 |  |  | $ | 95,920 |  |  | $ | 96,909 |
Mortgage notes payable, net | $ | 2,909,081 |  |  | $ | 3,144,150 |  |  | $ | 2,922,408 |  |  | $ | 2,984,956 |
Unsecured senior notes, net | 9,639,287 |  |  | 10,620,527 |  |  | 8,390,459 |  |  | 8,826,375 |
Unsecured line of credit | — |  |  | — |  |  | — |  |  | — |
Unsecured term loan, net | 499,390 |  |  | 500,326 |  |  | 498,939 |  |  | 500,561 |
Total | $ | 13,047,758 |  |  | $ | 14,265,003 |  |  | $ | 11,811,806 |  |  | $ | 12,311,892 |
Dividends Declared | The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or declared in 2020 and during the year ended December 31, 2019:
Record Date |  | Payment Date |  | Dividend (Per Share) |  | Distribution (Per Unit)
December 31, 2020 |  | January 28, 2021 |  | $0.98 |  |  | $0.98 |
September 30, 2020 |  | October 30, 2020 |  | $0.98 |  |  | $0.98 |
June 30, 2020 |  | July 31, 2020 |  | $0.98 |  |  | $0.98 |
March 31, 2020 |  | April 30, 2020 |  | $0.98 |  |  | $0.98 |
December 31, 2019 |  | January 30, 2020 |  | $0.98 |  |  | $0.98 |
December 31, 2019 |  | January 30, 2020 |  | $0.98 |  |  | $0.98 |
September 30, 2019 |  | October 31, 2019 |  | $0.95 |  |  | $0.95 |
June 28, 2019 |  | July 31, 2019 |  | $0.95 |  |  | $0.95 |
March 29, 2019 |  | April 30, 2019 |  | $0.95 |  |  | $0.95 |
December 31, 2018 |  | January 30, 2019 |  | $0.95 |  |  | $0.95 |
Dividend Paid [Member] |
Summary Of Significant Accounting Policies [Line Items] |
Dividends Declared | The tax treatment of common dividends per share for federal income tax purposes is as follows:
|  | For the year ended December 31,
|  | 2020 |  | 2019 |  | 2018
|  | Per Share |  | % |  | Per Share |  | % |  | Per Share |  | %
Ordinary income |  | $ | 2.52 |  |  | 64.91 | % |  | $ | 2.99 |  |  | 94.84 | % |  | $ | 2.79 |  |  | 78.17 | %
Capital gain income |  | 0.99 |  |  | 25.49 | % |  | 0.16 |  |  | 5.16 | % |  | 0.78 |  |  | 21.83 | %
Return of capital |  | 0.37 |  |  | 9.60 | % |  | — |  |  | — | % |  | — |  |  | — | %
Total |  | $ | 3.88 |  | (1) | 100.00 | % |  | $ | 3.15 |  | (2) | 100.00 | % |  | $ | 3.57 |  | (3) | 100.00 | %
_____________ (1)The fourth quarter 2020 regular quarterly dividend was $0.98 per common share, all of which was allocable to 2021. (2)The fourth quarter 2019 regular quarterly dividend was $0.98 per common share of which approximately $0.04 per common share was allocable to 2019 and approximately $0.94 per common share was allocable to 2020. (3)The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share was allocable to 2019.

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