| Document and Entity Information | May 20, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 20, 2021 |
| Entity Registrant Name | BEAM THERAPEUTICS INC. |
| Entity Central Index Key | 0001745999 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity File Number | 001-39208 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 81-5238376 |
| Entity Address, Address Line One | 26 Landsdowne St. |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02139 |
| 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 |
