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Stock Option and Grant Plan - Additional Information (Details) - USD ($) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Feb. 29, 2020 | May 31, 2019 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Oct. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense |  |  | $ 120,662,000 | $ 98,647,000 | $ 84,321,000 |
Weighted-average grant date fair value per share of stock options granted |  |  | $ 17.13 | $ 27.88 | $ 40.86 |
Aggregate intrinsic value of stock options exercised |  |  | $ 10,700,000 | $ 20,000,000 | $ 23,400,000 |
Weighted-average exercise price of stock options |  |  | $ 9.94 | $ 7.69 | $ 5.64 |
Employee Stock Option |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost related to unvested stock options |  |  | $ 86,800,000 |  |  |
Unrecognized compensation cost, cost to recognize over a weighted-average period |  |  | 2 years 4 months 24 days |  |  |
Restricted Stock |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost, cost to recognize over a weighted-average period |  |  | 2 years 4 months 24 days |  |  |
Aggregate fair value of restricted shares vested |  |  | $ 35,600,000 | $ 13,800,000 | $ 53,100,000 |
Unrecognized stock-based compensation expense, expected to vest |  |  | $ 68,400,000 |  |  |
Restricted Stock | Maximum |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Vesting period |  |  | 4 years |  |  |
Restricted Stock | Minimum |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Vesting period |  |  | 2 years |  |  |
2017 Plan | Employee Stock Option |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Expiration period |  | 10 years |  |  |  |
2019 Plan |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Maximum number of shares for future issuance |  |  |  |  |  | 3,700,000
Number of shares reserved for future issuance |  |  | 13,773,507 |  |  |
Number of shares available for future issuance |  |  | 1,591,110 |  |  |
2019 Plan | Common Stock | Maximum |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Annual percentage increase in shares authorized |  |  | 4.00% |  |  |
2019 Plan | From 2017 Plan Shares | Maximum |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Maximum number of shares for future issuance |  |  |  |  |  | 5,639,818
2019 Employee Stock Purchase Plan |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |
Number of shares available for future issuance |  |  | 2,928,706 |  |  |
Number of shares issued |  |  | 135,187 | 130,403 | 70,073 |
Stock-based compensation expense |  |  | $ 1,300,000 | $ 1,300,000 | $ 1,500,000 |
Common stock, shares description | In February 2020, the Company’s board of directors adopted the Beam Therapeutics Inc. 2019 Employee Stock Purchase Plan, or ESPP, which was approved by the Company’s stockholders. Pursuant to the ESPP, certain employees of the Company, excluding consultants and non-employee directors, are eligible to purchase common stock of the Company at a reduced rate during offering periods. The ESPP permits participants to purchase common stock using funds contributed through payroll deductions, subject to a calendar year limit of $25,000 and at a purchase price of 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the applicable purchase date, which will be the final trading day of the applicable purchase period. |  |  |  |  |
Maximum amount allowed to purchase common stock using payroll deduction | $ 25,000 |  |  |  |  |
Percentage of common stock purchase price lower of the fair market value | 85.00% |  |  |  |  |

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