| Cover | May 10, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | May 10, 2022 |
| Entity Registrant Name | First Watch Restaurant Group, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-40866 |
| Entity Tax Identification Number | 82-4271369 |
| Entity Address, Address Line One | 8725 Pendery Place |
| Entity Address, Address Line Two | Suite 201 |
| Entity Address, City or Town | Bradenton |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 34201 |
| City Area Code | 941 |
| Local Phone Number | 907-9800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $0.01 par value |
| Trading Symbol | FWRG |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Security Exchange Name | NASDAQ |
| Entity Central Index Key | 0001789940 |
| Amendment Flag | false |
