| Document And Entity Information | May 02, 2022 |
| Document Information [Line Items] | |
| Entity, Registrant Name | RBB BANCORP |
| Document, Type | 8-K/A |
| Document, Period End Date | May 2, 2022 |
| Entity, Incorporation, State or Country Code | CA |
| Entity, File Number | 001-36094 |
| Entity, Tax Identification Number | 52-1652138 |
| Entity, Address, Address Line One | 1055 Wilshire Blvd., 12th floor |
| Entity, Address, City or Town | Los Angeles |
| Entity, Address, State or Province | CA |
| Entity, Address, Postal Zip Code | 90017 |
| City Area Code | 213 |
| Local Phone Number | 627-9888 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | RBB |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | true |
| Entity, Ex Transition Period | false |
| Amendment Description | Share Buyback update |
| Amendment Flag | true |
| Entity, Central Index Key | 0001499422 |
