| Document and Entity Information | Sep. 06, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 6, 2021 |
| Entity Registrant Name | Repare Therapeutics Inc. |
| Entity Incorporation, State or Country Code | A8 |
| Entity File Number | 001-39335 |
| Entity Tax Identification Number | 00-0000000 |
| Entity Address, Address Line One | 7210 Frederick-Banting |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | St-Laurent |
| Entity Address, State or Province | QC |
| Entity Address, Country | CA |
| Entity Address, Postal Zip Code | H4S 2A1 |
| City Area Code | 857 |
| Local Phone Number | 412-7018 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common shares, no par value |
| Trading Symbol | RPTX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001808158 |
