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Stock Option and Incentive Plan (Narrative) (Details) - USD ($) $ in Millions |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | ---
Feb. 06, 2020 | Feb. 04, 2020 | Feb. 09, 2019 | Feb. 04, 2018 | Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting Period |  |  |  |  | 4 years
MYLTIP 2017 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards | $ 17.6 |  |  |  |
Final awards percentage of target | 83.80% |  |  |  |
Forfeitures, in units | 270,942 |  |  |  |
MYLTIP 2016 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards |  |  | $ 13.6 |  |
Final awards percentage of target |  |  | 69.50% |  |
Forfeitures, in units |  |  | 364,980 |  |
MYLTIP 2015 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards |  |  |  | $ 3.6 |
Final awards percentage of target |  |  |  | 22.00% |
Forfeitures, in units |  |  |  | 337,847 |
2012 Stock Option and Incentive Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Description |  |  |  |  | At Boston Properties, Inc.’s 2012 annual meeting of stockholders held on May 15, 2012, its stockholders approved the Boston Properties, Inc. 2012 Stock Option and Incentive Plan (the “2012 Plan”). The 2012 Plan replaced the 1997 Stock Option and Incentive Plan (the “1997 Plan”). The material terms of the 2012 Plan include, among other things: (1) the maximum number of shares of common stock reserved and available for issuance under the 2012 Plan is the sum of (i) 13,000,000 newly authorized shares, plus (ii) the number of shares available for grant under the 1997 Stock Plan immediately prior to the effective date of the 2012 Plan, plus (iii) any shares underlying grants under the 1997 Plan that are forfeited, canceled or terminated (other than by exercise) in the future; (2) “full-value” awards (i.e., awards other than stock options) are multiplied by a 2.32 conversion ratio to calculate the number of shares available under the 2012 Plan that are used for each full-value award, as opposed to a 1.0 conversion ratio for each stock option awarded under the 2012 Plan; (3) shares tendered or held back for taxes will not be added back to the reserved pool under the 2012 Plan; (4) stock options may not be re-priced without stockholder approval; and (5) the term of the 2012 Plan is for 10 years from the date of stockholder approval.
MYLTIP 2020 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting Period |  | 4 years |  |  |
TSR measurement (in years) |  | three-year |  |  |
Minimum earned awards |  | 0 |  |  |
Maximum Earned Awards |  | 203,278 |  |  |
Earned awards - Target |  | 101,638 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights |  | Earned awards (if any) will vest 50% on February 3, 2023 and 50% on February 3, 2024, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 3, 2023, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2020 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units. |  |  |
Value of MYLTIP Awards |  | $ 13.7 |  |  |

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