| Document And Entity Information | Aug. 14, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 14, 2021 |
| Entity Registrant Name | Viracta Therapeutics, Inc. |
| Entity Central Index Key | 0001061027 |
| Entity Emerging Growth Company | false |
| Entity File Number | 000-51531 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 94-3295878 |
| Entity Address, Address Line One | 2533 S. Coast Hwy. 101, Suite 210 |
| Entity Address, City or Town | Cardiff |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92007 |
| City Area Code | (858) |
| Local Phone Number | 400-8470 |
| 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 | VIRX |
| Security Exchange Name | NASDAQ |
