| Document and Entity Information | Nov. 05, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 5, 2020 |
| Entity Registrant Name | ARCUS BIOSCIENCES, INC. |
| Entity Central Index Key | 0001724521 |
| Entity Incorporation, State or Country Code | DE |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity File Number | 001-38419 |
| Entity Tax Identification Number | 47-3898435 |
| Entity Address, Address Line One | 3928 Point Eden Way |
| Entity Address, City or Town | Hayward |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94545 |
| City Area Code | 510 |
| Local Phone Number | 694-6200 |
| 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 $0.0001 Per Share |
| Trading Symbol | RCUS |
| Security Exchange Name | NYSE |
