| Document And Entity Information | Aug. 01, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 01, 2022 |
| Entity Registrant Name | Beam Therapeutics Inc. |
| Entity Central Index Key | 0001745999 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-39208 |
| Entity Incorporation, State or Country Code | DE |
| 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 |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | BEAM |
| Security Exchange Name | NASDAQ |
