| Document and Entity Information | Dec. 03, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 3, 2020 |
| Entity Registrant Name | SUTRO BIOPHARMA, INC. |
| Entity Central Index Key | 0001382101 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity File Number | 001-38662 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 47-0926186 |
| Entity Address, Address Line One | 310 Utah Avenue |
| Entity Address, Address Line Two | Suite 150 |
| Entity Address, City or Town | South San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94080 |
| City Area Code | 650 |
| Local Phone Number | 392-8412 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Security12b Title | Common Stock, $0.001 par value |
| Trading Symbol | STRO |
| Security Exchange Name | NASDAQ |
