| Document and Entity Information | Feb. 28, 2022 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001745999 |
| Document Type | 8-K |
| Document Period End Date | Feb. 28, 2022 |
| Entity Registrant Name | BEAM THERAPEUTICS INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39208 |
| Entity Tax Identification Number | 81-5238376 |
| Entity Address, Address Line One | 238 Main Street |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02142 |
| City Area Code | (857) |
| Local Phone Number | 327-8775 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | BEAM |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
