| Document and Entity Information Document | May 09, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | May 09, 2023 |
| Entity Registrant Name | GUARDANT HEALTH, INC. |
| Entity Central Index Key | 0001576280 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38683 |
| Entity Tax Identification Number | 45-4139254 |
| Entity Address, Address Line One | 3100 Hanover Street |
| Entity Address, City or Town | Palo Alto |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94304 |
| City Area Code | 855 |
| Local Phone Number | 698-8887 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, $0.00001 par value per share |
| Trading Symbol | GH |
| Security Exchange Name | NASDAQ |
