| Document and Entity Information | Nov. 05, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | POTBELLY CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0001195734 |
| Document Type | 8-K |
| Document Period End Date | Nov. 5, 2020 |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36104 |
| Entity Tax Identification Number | 36-4466837 |
| Entity Address, Address Line One | 111 N. Canal Street |
| Entity Address, Address Line Two | Suite 850 |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60606 |
| City Area Code | (312) |
| Local Phone Number | 951-0600 |
| 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 | PBPB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
