Document And Entity Information - USD ($)	Dec. 31, 2021	Mar. 21, 2022	Jun. 30, 2021
Document Information [Line Items]
Entity, Registrant Name	RBB BANCORP
Document, Type	10-K/A
Document, Annual Report	true
Document, Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document, Fiscal Period Focus	FY
Document, Fiscal Year Focus	2021
Document, Transition Report	false
Entity, File Number	001-38149
Entity, Incorporation, State or Country Code	CA
Entity, Tax Identification Number	27-2776416
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
Title of 12(b) Security	Common Stock, No Par Value
Trading Symbol	RBB
Security Exchange Name	NASDAQ
Entity, Well-known Seasoned Issuer	No
Entity, Voluntary Filers	No
Entity, Current Reporting Status	Yes
Entity, Interactive Data, Current	Yes
Entity, Filer Category	Accelerated Filer
Entity, Small Business	false
Entity, Emerging Growth Company	true
Entity, Ex Transition Period	false
ICFR Auditor Attestation Flag	true
Entity, Shell Company	false
Entity, Public Float			$ 378,802,944
Entity, Common Stock Shares, Outstanding		19,453,941
Auditor Name	Eide Bailly LLP
Auditor Location	Laguna Hills, California
Auditor Firm ID	286
Amendment Description	This Amendment No. 1 on Form 10-K/A (“Amendment No. 1”) is being filed to amend RBB Bancorp’s (together with its consolidated subsidiaries, the “Company”) Annual Report on Form 10-K for the fiscal year ended December 31, 2021 (“Original Filing”), filed with the U.S. Securities and Exchange Commission (“SEC”) on March 11, 2022 (“Original Filing Date”). The sole purpose of this Amendment No. 1 is to correct the previously filed Exhibit Index, which inadvertently did not incorporate by reference previously-filed exhibits or include a reference to the date, and the filing with which, such exhibits were previously filed and to file additional exhibits, which were inadvertently omitted from the Exhibit Index.   As required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), the Company’s principal executive officer and principal financial officer are providing new currently dated certifications required pursuant to Exchange Act Rules 13a-14(a) and 15d-14(a), as adopted pursuant Section 302 of the Sarbanes-Oxley Act of 2002, which are attached hereto.   Except as described above, this Amendment No. 1 does not amend, update or change any other items or disclosures in the Original Filing. This Amendment No. 1 speaks only as of the Original Filing Date, and the Company has not undertaken herein to amend, supplement or update any information contained in the Original Filing to give effect to any subsequent events. Accordingly, this Amendment No. 1 should be read in conjunction with the Company’s filings made with the SEC subsequent to the filing of the Original Filing, including any amendment to those filings.
Amendment Flag	true
Entity, Central Index Key	0001499422