Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] FHLB advances rbb_InterestOnOtherBorrowedFunds Amount of interest expense on borrowed funds classified as other. Trading Arrangement: Trading Arrangement [Axis] PGBH Trust PGBH Trust [Member] Related to PGBH Trust Subordinated debt Subordinated Debt Maximum Maximum [Member] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Short-Term Debt, Type [Axis] Short-Term Debt, Type [Axis] Title of 12(b) Security Title of 12(b) Security Used in dilutive EPS Net Income (Loss) Available to Common Stockholders, Diluted Carrying Value Reported Value Measurement [Member] Subsequent Event Subsequent Event [Member] Adjustment to Compensation, Amount Adjustment to Compensation Amount Actual, ratio Banking Regulation, Total Risk-Based Capital Ratio, Actual Pledged Status [Axis] Pledged Status [Axis] Financial Instrument [Axis] Financial Instrument [Axis] Recognition of operating lease liabilities Recognition of operating lease liabilities Represents amount of operating lease liabilities recognized during the period. To Be Well-Capitalized Under Prompt Corrective Action Provisions, ratio TierOneRiskBasedCapitalRequiredPlusCapitalConversationBufferFullyPhasedInToRiskWeightedAssets Represents tier one risk based capital required plus capital conversation buffer fully phased in to risk weighted assets. Financing Receivable, Nonaccrual [Table] Financing Receivable, Nonaccrual [Table] Segment Reporting [Abstract] Schedule of Estimated CDI Amortization Expense for Future Years Intangible Asset, Finite-Lived, and Capitalized Cost, Software to be Sold, Leased, or Marketed, Estimated Amortization Expense [Table Text Block] Core deposit intangible amortization Core deposit intangible amortization The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. Derivative Instrument [Axis] Derivative Instrument [Axis] Restricted stock units vested (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Servicing assets Servicing Asset at Fair Value, Amount Measurement Frequency [Axis] Measurement Frequency [Axis] Consolidated Entities [Axis] Consolidated Entities [Axis] Weighted average share price (in dollars per share) Shares Acquired, Average Cost Per Share Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Advance With Quarterly Call, One Year Lock Out Advance With Quarterly Call, One Year Lock Out [Member] Represents advance with quarterly call, 1 year initial lock out. The 2017 Omnibus Stock Incentive Plan The 2017 Omnibus Stock Incentive Plan [Member] Represents the 2017 Omnibus Stock Incentive Plan. Subordinated Borrowings [Abstract] Minimum Required for Capital Adequacy Purposes, ratio Banking Regulation, Total Risk-Based Capital Ratio, Capital Adequacy, Minimum Doubtful Doubtful [Member] DEPOSITS Deposit Liabilities Disclosures [Text Block] Leases [Abstract] Other comprehensive (loss)/income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Loans held for investment Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process Schedule of Bank’s Capital Amounts and Ratios and the Related Regulatory Requirements Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Actual Banking Regulation, Tier 1 Risk-Based Capital, Actual Consolidated Entities [Domain] Consolidated Entities [Domain] FHLB, San Francisco Federal Home Loan Bank of San Francisco [Member] RELATED PARTY TRANSACTIONS Related Party Transactions Disclosure [Text Block] YTD gross charge-offs, Prior Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff Unrealized Losses, AFS, Total Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Prior Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year Outstanding, beginning balance (in shares) Outstanding, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Schedule of Loan Modifications Financing Receivable, Modified [Table Text Block] Advance With One Time Call, Three Month Lock Out, Three Advance With One Time Call, Three Month Lock Out, Three [Member] Advance With One Time Call, Three Month Lock Out, Three Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Number of reportable segments Number of Reportable Segments Beginning of period End of period Servicing Asset at Amortized Cost Short-Term Debt, Type [Domain] Short-Term Debt, Type [Domain] Amortized Cost Amortized Cost, AFS, Total Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Amortized Cost, HTM, More than One Year to Five Years Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Rolling after One through Five Years Entity Address, City or Town Entity Address, City or Town Grants (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Federal Home Loan Bank (FHLB) stock Federal Home Loan Bank Stock Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Number of branches Number Of Branches The number of branches operated during the period. Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Title and Position [Domain] Title and Position [Domain] 2028 Time Deposit Maturities, Year Two YTD gross charge-offs, 2026/2025 Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff Total Intangible Asset, Finite-Lived, after Accumulated Amortization Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Federal Home Loan Bank Branch [Axis] Federal Home Loan Bank Branch [Axis] FHLB advances Federal Home Loan Bank Borrowings, Fair Value Disclosure Additions to servicing assets Additions to servicing assets Additions to the servicing asset during the period. Level 2 Fair Value, Inputs, Level 2 [Member] 4.00% Fixed To Floating Rate Subordinated Debentures due 2031 Four Percent Fixed To Floating Rate Subordinated Debentures Due April First Two Thousand Thirty One [Member] Represents 4.00% fixed to floating rate subordinate debentures due April 1, 2031. Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Total other comprehensive (loss)/income Other comprehensive income (loss), net of taxes Other Comprehensive Income (Loss), Net of Tax Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] 90 Days or More Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Commitment with fixed rate Financing Receivable, Commitment with Fixed Rate, Amount Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Depreciation and amortization of premises and equipment Depreciation and amortization of premises and equipment The aggregate expense recognized in the current period that allocates the cost of premises and equipment to periods that benefit from use of the assets. Class of Treasury Stock [Table] Class of Treasury Stock [Table] Schedule of Segment Information Segment Reporting [Table Text Block] Use of Estimates in the Preparation of Financial Statements Use of Estimates, Policy [Policy Text Block] To Be Well-Capitalized Under Prompt Corrective Action Provisions Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount Represents common equity tier once capital required plus capital conversion buffer fully phased in amount. Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] 2025 and 2026 Repurchase Plan 2025 and 2026 Share Repurchase Programs [Member] 2025 and 2026 Share Repurchase Programs. Fair Value, AFS, More than One Year to Five Years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Schedule of Future Minimum Rent Payments Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Allowance for loan losses Beginning balance Ending balance Allowance for loan losses Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Document Period End Date Document Period End Date To Be Well-Capitalized Under Prompt Corrective Action Provisions Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount Represents tier one risk based capital required plus capital conversation buffer fully phased in amount. Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Aggregate principal amount Debt Instrument, Face Amount 2028 Lessee, Operating Lease, Liability, to be Paid, Year Two Revolving Converted to Term During the Period Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan Effective stated rate (as a percent) Effective Stated Rate (as a percent) Debt Instrument, Interest Rate, Effective Percentage Level 1/2/3 Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Related income tax effect OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Amortized Cost, AFS, More than Ten Years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Greater than FDIC Limit of $250,000 Greater than FDIC Limit of $250,000 [Member] Greater than FDIC Limit of $250,000 Participating Mortgage Loans [Table] Participating Mortgage Loans [Table] Advance With Quarterly Call, Three Month Lock Out Advance With Quarterly Call, Three Month Lock Out [Member] Advance With Quarterly Call, Three Month Lock Out Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Single-family residential mortgage Mortgage Loans Mortgages [Member] Payoffs Servicing Asset at Amortized Cost, Disposals EARNINGS PER SHARE Earnings Per Share [Text Block] Net income per share Earnings Per Share [Abstract] Offsetting Liabilities [Line Items] Offsetting Liabilities [Line Items] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Schedule of Amortization of Mortgage Servicing Rights Netted Against Loan Servicing Fee Income Servicing Asset at Amortized Cost [Table Text Block] Total liabilities Liabilities Trading Symbol Trading Symbol Discount rate Measurement Input, Discount Rate [Member] Available for sale (amortized cost of $411,901 and $426,145 at September 30, 2026 and December 31, 2025) Fair Value Fair Value, AFS, Total Investment securities – AFS Debt Securities, Available-for-Sale, Excluding Accrued Interest Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward] Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward] Business Assets Business Assets [Member] Relating to business assets. Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Company Selected Measure Name Company Selected Measure Name Purchases Payments to Acquire Debt Securities, Available-for-Sale Net increase of investment in qualified affordable housing projects rbb_PurchaseOfInvestmentInQualifiedAffordableHousingProjects The payments during the period for the purchase of investment in qualified affordable housing projects. Income Tax Disclosure [Abstract] Offsetting Liabilities [Table] Offsetting Liabilities [Table] Fair Value, HTM, More than One Year to Five Years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Term loan balance for 2026/2025 Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year Operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Unrealized Losses, HTM, Less than Twelve Months rbb_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1 Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months. Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Actual Banking Regulation, Tier 1 Leverage Capital, Actual Deferred tax expense Deferred Income Taxes and Tax Credits Financing Receivable, Modified [Line Items] Financing Receivable, Modified [Line Items] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Remaining secured borrowing capacity Line of Credit Facility, Current Borrowing Capacity Financing receivable, modified, commitment to lend Financing Receivable, Modified, Commitment to Lend Award Timing Predetermined Award Timing Predetermined [Flag] Intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value Interest and dividend income: Interest and Dividend Income, Operating [Abstract] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Stock-based compensation, net APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Level 1 Fair Value, Inputs, Level 1 [Member] Required assets to liabilities ratio after dividend effect Required Assets To Liabilities Ratio After Dividend Effect Represents required assets to liabilities ratio after dividend effect. Effective tax rate (as a percent) Effective Income Tax Rate Reconciliation, Percent Employee Retention Credit Employee Retention Credit [Member] Represents Employee Retention Credit. Dilutive effect of outstanding stock options & RSUs (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Repurchase of common stock Stock Repurchased and Retired During Period, Value Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Change in operating lease liabilities Increase (Decrease) in Operating Lease Liability Proceeds from sales of loans originally classified as HFI Proceeds from sales of loans originally classified as HFI The proceeds from the sale of loan originally held for investment. MBS: Residential Residential Mortgage-Backed Securities [Member] Long-term debt Long-Term Debt, Fair Value Municipal securities Municipal Securities [Member] Debt securities issued by state, city or local governments or the agencies operated by state, city or local governments. Plan Name [Domain] Plan Name [Domain] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Beginning balance (in dollars per share) Ending balance (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price Federal Home Loan Bank Branch [Domain] Federal Home Loan Bank Branch [Domain] Right-of-use assets - operating leases ROU assets Operating Lease, Right-of-Use Asset Offsetting Assets [Table] Offsetting Assets [Table] Amortized Cost, AFS, One Year or Less Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One Fair Value Disclosures [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] INVESTMENT SECURITIES Investment in Debt and Equity Securities and Other Trading Assets [Text Block] Expiration Date Trading Arrangement Expiration Date Net decrease in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Excluding Exchange Rate Effect, Including Discontinued Operation Common Equity Tier 1 Risk Based Capital Ratio Banking Regulation, Common Equity Tier 1 Risk-Based Capital [Abstract] Advance With One Time Call, Nine Month Lock Out, Three Advance With One Time Call, Nine Month Lock Out, Three [Member] Advance With One Time Call, Nine Month Lock Out, Three Gross Unrealized Gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Total shareholders’ equity Beginning balance Ending balance Shareholders’ equity Equity, Including Portion Attributable to Noncontrolling Interest Subordinated Debt Subordinated Debt [Member] Time-based Restricted Stock Units TimebasedRestrictedStockUnits [Member] Represents Time-based Restricted Stock Units. Options exercisable (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Default rate Measurement Input, Default Rate [Member] Common stock, par value (in dollars per share) Common Stock, No Par Value Deposits Deposits, Fair Value Disclosure Commercial real estate Commercial Real Estate [Member] Investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Construction and land development Construction And Land Development Loans [Member] Represents information related to construction and land development loans. Unrecognized stock-based compensation expense Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Fees and service charges on deposit accounts Fees And Service Charges On Deposit Accounts [Member] Represents information related to fees and service charges on deposit accounts. Segments [Domain] Segments [Domain] Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Federal Home Loan Bank, Advances, Option [Domain] Federal Home Loan Bank, Advances, Option [Domain] BORROWING ARRANGEMENTS Debt Disclosure [Text Block] Participating Mortgage Loans [Line Items] Participating Mortgage Loans [Line Items] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Government Assistance, Type [Axis] Government Assistance, Type [Axis] Loans held for sale Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance Debt instrument, fixed interest rate (as a percent) Debt Instrument, Interest Rate, Stated Percentage Cash dividends on common stock Dividends, Common Stock, Cash % of Loan Class Financing Receivable, Modified in Period, to Total Financing Receivables, Percentage Minimum Required for Capital Adequacy Purposes Banking Regulation, Total Risk-Based Capital, Capital Adequacy, Minimum Offsetting Assets [Line Items] Offsetting Assets [Line Items] Assets Assets [Abstract] Payment Deferral Payment Deferral [Member] Deposit Liability [Line Items] Deposit Liability [Line Items] Schedule of Loans HFI by Loan Portfolio Segment, Risk Rating and Vintage Year Financing Receivable Credit Quality Indicators [Table Text Block] On a non-recurring basis: Fair Value, Nonrecurring [Member] Insurance and regulatory assessments Insurance and regulatory assessments The amount of expense for insurance and regulatory assessments. Insider Trading Policies and Procedures [Line Items] Municipal tax-exempt securities Nontaxable Municipal Bonds [Member] SBA agency securities Small Business Administration Agency Securities [Member] Securities issued by the Small Business Association agency. Commercial real estate Real estate: Commercial Real Estate Portfolio Segment [Member] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] Servicing asset, measurement input (as a percent) Servicing Asset, Measurement Input Antidilutive securities excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Weighted average rate (as a percent) Rate Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End Entity Central Index Key Entity Central Index Key Accrued interest and other liabilities Accrued interest and other liabilities Amount of interest incurred but not yet paid, and liabilities classified as other. Net interest income after provision for credit losses Interest Income (Expense), after Provision for Loan Loss Other Other Loans [Member] Represents information related to other loans. Equity [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Pledging Purpose [Axis] Pledging Purpose [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Advance With One Time Call, One Year Lock Out Advance With One Time Call, One Year Lock Out [Member] Relating to Advance With One Time Call, One Year Lock Out. Commercial and similar letters of credit Commercial And Similar Letters Of Credit [Member] Represents information related to commercial and similar letters of credit. Financing Receivable, Modified [Table] Financing Receivable, Modified [Table] Fair value of the options vested Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested in Period, Fair Value Outstanding Options Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward] Debt instrument, basis point Variable rate of interest (as a percent) Debt Instrument, Basis Spread on Variable Rate Variable Rate [Domain] Variable Rate [Domain] Nonaccrual Loans with no ALL Financing Receivable, Excluding Accrued Interest, Nonaccrual, No Allowance Loans originated for sale, net Payment for Origination and Purchase, Loan, Held-for-Sale Accumulated Other Comprehensive (Loss)/Income, net AOCI Attributable to Parent [Member] All Individuals All Individuals [Member] Cash dividends paid Payments of Dividends Valuation allowances and reserves, amount SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Cost not yet recognized, period for recognition (in years) Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Statement [Line Items] Statement [Line Items] Total assets Assets Total Assets Assets Term Extension Extended Maturity [Member] Total interest expense Interest expense Interest Expense, Operating Common stock, capital shares reserved for future issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Loans transferred to held for sale, net Loans transferred to held for sale, net Value of loans and leases held in the entity's portfolio (transferred from) transferred to loans and leases held-for-sale in noncash transactions Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax STOCK-BASED COMPENSATION Share-Based Payment Arrangement [Text Block] Occupancy and equipment expenses Occupancy, Net PEO PEO [Member] Noninterest-bearing demand Noninterest-Bearing Deposit Liabilities Goodwill Goodwill LOAN SERVICING Loan Servicing [Text Block] The entire disclosure for loan servicing. Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Number of Issuances, AFS, Total Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Retained Earnings Retained Earnings [Member] Loans held for investment, net of allowance for loan losses Held for Investment Loans [Member] Relating to held for investment loans. Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Schedule of Fair Value Hierarchy Level and Estimated Fair Value of Significant Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Financing Receivable, Past Due [Line Items] Financing Receivable, Past Due [Line Items] Corporate debt securities Corporate Debt Securities [Member] Diluted (in dollars per share) Diluted earnings per common share (in dollars per share) Earnings Per Share, Diluted Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] (Loss)/gain on other real estate owned (Loss)/gain on other real estate owned Amount of gains or loss on sale and transfer of other real estate owned. Amortization of intangible assets Intangible Asset, Finite-Lived, Amortization Expense Long-term debt and subordinated debentures Interest Expense, Long-Term Debt and Capital Securities Finite-Lived Intangible Assets [Line Items] Intangible Asset, Finite-Lived [Line Items] Term loan balance for 2023/2022 Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year Executive Officers, Directors and their Related Interests Executive Officers, Directors and their Related Interests [Member] Represents information related to executive officers, directors and their related interests. Additions Servicing Asset at Amortized Cost, Additions Share-Based Payment Arrangement [Abstract] Noninterest income, in scope Revenue from Contract with Customer, Excluding Assessed Tax Minimum Required for Capital Adequacy Purposes, ratio Banking Regulation, Tier 1 Leverage Capital Ratio, Capital Adequacy, Minimum Redemptions of long-term debt Repayments of Other Long-Term Debt Commitments to make loans Commitments to Make Loans [Member] Represents commitments to make loans. To Be Well-Capitalized Under Prompt Corrective Action Provisions Total Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount Represents capital required for capital conversation buffer fully phased in amount. Advance With One Time Call, Nine Month Lock Out Advance With One Time Call, Nine Month Lock Out [Member] Advance With One Time Call, Nine Month Lock Out Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Mortgage-backed securities Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member] Securities held to maturity: Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss [Abstract] Service charges and fees Service charges and fees The amount of service charges, fees, and income classified as other. Advance With One Time Call, Three Month Lock Out Advance With One Time Call, Three Month Lock Out [Member] Relating to Advance With One Time Call, Three Month Lock Out Equity securities Equity, Fair Value Disclosure TFC Trust TFC Statutory Trust [Member] Represents information related to TFC statutory trust. Title and Position [Axis] Title and Position [Axis] Weighted- Average Remaining Contractual Term in years Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract] Other real estate owned ("OREO") Other Real Estate Minimum Required for Capital Adequacy Purposes, ratio Banking Regulation, Tier 1 Risk-Based Capital Ratio, Capital Adequacy, Minimum Remainder of 2026 Time Deposit Maturities, Remainder of Fiscal Year Collateral Held [Axis] Collateral Held [Axis] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Revolving Financing Receivable, Excluding Accrued Interest, Revolving Schedule of Changes in the ACL Financing Receivable, Allowance for Credit Loss [Table Text Block] Common stock, shares issued (in shares) Common Stock, Shares, Issued Amortization expense Debt Amortization Expense Represents amortization expenses of debt. CMO: Commercial Commercial Collateralized Mortgage Obligations [Member] Related to commercial collateralized mortgage obligations. ACCRUED INTEREST AND OTHER ASSETS Other Assets Disclosure [Text Block] Time deposits acquired through internet listing services Time Deposits Acquired Through Internet Listing Services [Member] Represents Time Deposits Acquired Through Internet Listing Services. Minimum Required for Capital Adequacy Purposes Banking Regulation, Common Equity Tier 1 Risk-Based Capital, Capital Adequacy, Minimum Unrealized Losses, AFS, Twelve Months or More Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Product and Service [Domain] Product and Service [Domain] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Fair Value, HTM, Total Debt Securities, Held-to-Maturity, Unrealized Loss Position, Fair Value 1 Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position. Gain on OREO Net gain on OREO Gains (Losses) on Sales of Other Real Estate Other income Other Service Income [Member] Represents information related to other service income. Noninterest expense: Noninterest Expense [Abstract] Core deposit intangibles Intangible Assets, Current Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Marketing and business promotion Marketing and Advertising Expense 2029 Lessee, Operating Lease, Liability, to be Paid, Year Three Termination Date Trading Arrangement Termination Date Affordable Housing Partnerships and SBIC Funds AffordableHousingPartnershipsAndSbicFunds [Member] Relating to affordable housing partnerships and SBIC funds. Other Commitments [Axis] Other Commitments [Axis] Stock repurchase program, remaining authorized shares (in shares) Share Repurchase Program, Remaining Authorized, Number of Shares Subsequent Events [Abstract] Time deposits $250,000 and under Time deposits $250,000 and under The amount of time deposits with amounts of $250,000 and under. Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Expiration period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Fair Value as of Grant Date Award Grant Date Fair Value Collateral Pledged, Total Collateral Pledged [Member] (Loss)/gain on OREO Gain (Loss) on Disposition of Assets Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] Proceeds from FHLB advances Proceeds from FHLB advances The amount of increase in short-term advances from Federal Home Loan Bank. Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] FAIC Trust First American International Statutory Trust I 1 [Member] Represents information related to fist American international statutory trust !. Arrangement Duration Trading Arrangement Duration Minimum Required for Capital Adequacy Purposes Banking Regulation, Tier 1 Risk-Based Capital, Capital Adequacy, Minimum Entity Registrant Name Entity Registrant Name Entity Address, Postal Zip Code Entity Address, Postal Zip Code Unrealized Losses, AFS, Less than Twelve Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Loan Class Financing Receivable, Excluding Accrued Interest, Modified, Accumulated Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Unamortization balance Intangible Asset, Finite-Lived, before Accumulated Amortization Increase in cash surrender value of life insurance rbb_IncreaseDecreaseInCashSurrenderValueOfLifeInsurance The increase (decrease) during the period in the cash surrender value of life insurance policies. Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Collateralized mortgage obligations Collateralized Mortgage Obligations [Member] Loan Restructuring Modification [Axis] Loan Restructuring Modification [Axis] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] Option exercisable, weighted-average remaining contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted-Average Remaining Contractual Term Deposits from related party Related Party Deposit Liabilities Securities: Marketable Securities [Abstract] Award Type [Domain] Award Type [Domain] Remainder of 2026 Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year FAIR VALUE MEASUREMENTS AND FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] Government agency securities US Government Agencies Debt Securities [Member] Asset Pledged as Collateral Asset Pledged as Collateral [Member] Net increase in loans rbb_PaymentsForProceedsFromLoansAndLeasesExcludingLoansHeldForInvestment The net cash outflow or inflow for the increase (decrease) in the beginning and end of period of loan and lease balances which are not originated or purchased specifically for resale. Includes cash payments and proceeds, excluding loans held for investment. FAIC Trust FAIC Trust [Member] Related to FAIC trust. Accrued interest payable Interest Payable Fair Value Disclosure Fair value portion of interest payable on debt. Weighted average grant date fair value (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Option, Nonvested, Weighted Average Exercise Price Common stock, shares repurchased (in shares) Treasury Stock, Shares, Acquired 2027 Intangible Asset, Finite-Lived, Estimated Amortization Expense, Year One Debt Securities, Available-for-Sale, Allowance for Credit Loss [Line Items] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Line Items] Debt securities, HTM, allowance for credit loss Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest Segment net interest income and noninterest income Interest Income (Expense), Operating and Nonoperating Other assets Other Assets To Be Well-Capitalized Under Prompt Corrective Action Provisions Tier 1 Leverage Ratio, Minimum Required Plus Capital Conservation Buffer Fully Phased-In Amount Represents tire one leverage capital required plus capital conversion buffer fully phased in amount. 30-59 Days Financial Asset, 30 to 59 Days Past Due [Member] Interest expense Interest Expense, Debt Impact of weighting shares (in shares) Impact of weighting shares, shares (in shares) Represents weighted average number of shares impact. 2025 Repurchase Plan The 2025 Repurchase Plan [Member] Represents the 2025 Repurchase Plan. Actual Banking Regulation, Total Capital, Actual Noninterest income: Noninterest Income [Abstract] Intangible Asset, Finite-Lived [Table] Intangible Asset, Finite-Lived [Table] Capital conservation buffer Capital Conservation Buffer Represents information related to capital conservation buffer. Amortized Cost, HTM, More than Ten Years Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years Non-NEOs Non-NEOs [Member] Net (decrease) increase in time deposits Increase (Decrease) in Time Deposits 2028 Intangible Asset, Finite-Lived, Estimated Amortization Expense, Year Two Under FDIC Limit of $250,000 Under FDIC Limit of $250,000 [Member] Under FDIC Limit of $250,000 Savings, NOW and money market accounts Deposits, Money Market Deposits and Negotiable Order of Withdrawal (NOW) LEASES Lessee, Operating Leases [Text Block] Thereafter Lessee Operating Lease, Liability To Be Paid, After Year Four Amount of lessee's undiscounted obligation for lease payment for operating lease due after fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Amortized Cost, AFS, More than Five Years to Ten Years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Common stock repurchased, net of repurchase costs Payments for Repurchase of Common Stock Statistical Measurement [Axis] Statistical Measurement [Axis] ICS deposits Ics [Member] Represents ICS (Insured Cash Sweeps). Commercial and industrial Commercial and Industrial [Member] Portfolio segment of the company's total financing receivables related to commercial and industrial receivables. Amount Long-Term Federal Home Loan Bank Advances Award Type [Axis] Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Residential Real Estate Real Estate [Member] Available-for sale, amortized cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, after Allowance for Credit Loss Retained earnings Retained Earnings (Accumulated Deficit) Actual, ratio Banking Regulation, Common Equity Tier 1 Risk-Based Capital Ratio, Actual Product and Service [Axis] Product and Service [Axis] CRA and other equity investments Equity Securities, FV-NI Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Common Stock Common Stock [Member] Performance-based Restricted Stock Units PerformancebasedRestrictedStockUnits [Member] Represents Performance-based Restricted Stock Units. Tier 1 Risk-Based Capital Ratio Banking Regulation, Tier 1 Risk-Based Capital [Abstract] YTD gross charge-offs, 2022/2021 Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff Derivative Contract [Domain] Derivative Contract [Domain] Fair Value, HTM, Less than Twelve Months Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value 1 Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months. Total Past Due Financial Asset, Past Due [Member] Total liabilities and shareholders’ equity Liabilities and Equity Stock Options Share-Based Payment Arrangement, Option [Member] Non-controlling interest Equity, Attributable to Noncontrolling Interest Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Asset Class [Axis] Asset Class [Axis] Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] Business Combination, Description [Abstract] Schedule of Principal Balances of Mortgage and SBA Loans Serviced for Others Mortgage And Small Business Administration Loans Serviced For Others [Table Text Block] Tabular disclosure of mortgage and Small Business Administration loans serviced for others. Tabular List, Table Tabular List [Table Text Block] Additional paid-in capital Additional Paid in Capital 2029 Intangible Asset, Finite-Lived, Estimated Amortization Expense, Year Three Remainder of 2026 Intangible Asset, Finite-Lived, Estimated Amortization Expense, Remainder of Fiscal Year Name Awards Close in Time to MNPI Disclosures, Individual Name Amortized Cost, HTM, One Year or Less Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Rolling within One Year Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Outstanding, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value Valuation, Market Approach Valuation, Market Approach [Member] Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Transfer from loans to other real estate owned Real Estate Owned, Transfer to Real Estate Owned Preferred Stock - 100,000,000 shares authorized, no par value; none outstanding Preferred Stock, Value, Issued Adjustment to Compensation: Adjustment to Compensation [Axis] Investment in FHLB stock Investment in Federal Home Loan Bank Stock, Fair Value Disclosure Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Other Financial Institutions Other Financial Institutions [Member] Represents other financial institutions. Office expenses Supplies and Postage Expense 60-89 Days Financial Asset, 60 to 89 Days Past Due [Member] Brokered time deposits Brokered Time Deposits Amount of brokered time deposits. Schedule of Amortized Cost and Fair Value of Investment Securities Available for Sale Securities and Held to Maturity Schedule of Available for Sale Securities, and Held to Maturity [Table Text Block] Tabular disclosure of available-for-sale securities and held-to-maturity securities. Assets measured at fair value: Fair Value Assets, Fair Value Disclosure Proceeds from sales of OREO Proceeds from Sale of Foreclosed Assets Name Measure Name Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] COMMITMENTS AND CONTINGENCIES Commitments Disclosure [Text Block] Number of Issuances, AFS, Less than Twelve Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions Debt Instrument [Line Items] Debt Instrument [Line Items] FHLB stock FHLB stock The amount of dividend income in the period on Federal Home Loan Bank stock. Loans Interest and Fee Income, Financing Receivable Additional Paid-in Capital Additional Paid-in Capital [Member] Schedule of Financial Commitments Represents Credit Risk Schedule of Fair Value, off-Balance-Sheet Risks [Table Text Block] Impairment loss Goodwill, Impairment Loss Noninterest income, not in scope Revenue Not from Contract with Customer Accrued interest receivable Interest Receivable Name Trading Arrangement, Individual Name Single-family residential mortgages Single Family Residential Mortgages Loans [Member] Represents information related to single family residential mortgages loans. Cash and cash equivalents Cash and Cash Equivalent Operating lease, rental expense Operating Lease, Expense Company Selected Measure Amount Company Selected Measure Amount Subordinated debentures, net Subordinated debentures, net A debt instrument that embodies an unconditional obligation requiring the issuer to redeem the securities by transferring the assets at a specified or determinable date (or dates) or upon an event that is certain to occur. Income tax receivable Income Taxes Receivable Unused lines of credit Unused lines of Credit [Member] Secured Overnight Financing Rate (SOFR) Secured Overnight Financing Rate (SOFR) [Member] Accounts and Financing Receivables [Table] Accounts and Financing Receivables [Table] Measurement Input, Adjustment Measurement Input, Adjustment [Member] Measurement input using adjustments. Weighted-average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Non-PEO NEO Non-PEO NEO [Member] Tier 1 Leverage Ratio Banking Regulation, Tier 1 Leverage Capital [Abstract] Total noninterest expense Noninterest Expense Award Timing Method Award Timing Method [Text Block] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Accrued interest receivable for investment securities Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Proceeds from sales of fixed assets Proceeds from Sale of Property, Plant, and Equipment Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Restatement Determination Date: Restatement Determination Date [Axis] Options exercisable (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Exercise Price Schedule of Accrued Interest Receivable and Other Assets Schedule of Other Assets [Table Text Block] Level 2/3 Fair Value, Inputs, Level 2 and Level 3 [Member] Fair Value, Inputs, Level 2 and Level 3 Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Weighted-average common shares outstanding Weighted Average Number of Shares Outstanding, Diluted [Abstract] Statistical Measurement [Domain] Statistical Measurement [Domain] Document Fiscal Year Focus Document Fiscal Year Focus Preferred stock, par value (in dollars per share) Preferred Stock, No Par Value Other fees Other Fees [Member] Represents information related to other fees. RSUs Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Total deposits Deposits Total Deposits Deposits Common Stock - 100,000,000 shares authorized, no par value; 16,827,168 shares issued and outstanding at September 30, 2026 and 17,057,397 shares issued and outstanding at December 31, 2025 Common Stock, Value, Issued 2027 Lessee, Operating Lease, Liability, to be Paid, Year One Restricted stock units vesting Payment, Tax Withholding, Share-Based Payment Arrangement Schedule of Borrowing Arrangements Federal Home Loan Bank, Advances [Table Text Block] Amortized Cost, HTM, More than Five Years to Ten Years Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years Restatement Determination Date Restatement Determination Date Unrealized Losses, HTM, Total rbb_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLoss1 Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position. Other expenses Other Noninterest Expense Amendment Flag Amendment Flag Thereafter Finite Lived Intangible Assets Amortization Expense After Year Four Amount of amortization for asset, excluding financial asset and goodwill, lacking physical substance with finite life expected to be recognized after fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Gross Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Standby letters of credit Standby Letters of Credit [Member] FHLB, Secure Advances Federal Home Loan Bank Secured Line of Credit [Member] Represents information related to the Federal Home Loan Bank secured line of credit. Investments [Domain] Investments [Domain] FHLB, Advances Federal Home Loan Bank Advances [Member] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] TFC Trust TFC Trust [Member] Related to TFC Trust. Entity Address, State or Province Entity Address, State or Province Unrealized Losses, HTM, Twelve Months or More rbb_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss1 Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer. Nonaccrual Loans Financing Receivable, Excluding Accrued Interest, Nonaccrual PEO Total Compensation Amount PEO Total Compensation Amount LIHTC investments Investment, Proportional Amortization Method, Elected, Amount 2027 Time Deposit Maturities, Year One Share Repurchase Program [Domain] Share Repurchase Program [Domain] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Measurement input Other measurement input Other Real Estate Owned, Measurement Input 2030 Lessee, Operating Lease, Liability, to be Paid, Year Four Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Interest-earning deposits with financial institutions Interest-earning deposits in other financial institutions Interest-Bearing Deposits in Banks and Other Financial Institutions Reserve for unfunded loan commitments Unfunded Loan Commitment [Member] Fair Value, AFS, More than Five Years to Ten Years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Nonaccrual, interest income Financing Receivable, Nonaccrual, Interest Income Total noninterest income Noninterest Income 2026 Repurchase Plan The 2026 Repurchase Plan [Member] Represents the 2026 Repurchase Plan. LOANS AND ALLOWANCE FOR CREDIT LOSSES Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Federal funds sold and other Interest Income, Federal Funds Sold Time deposits Time deposits Time Deposits Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Used in basic EPS Net Income (Loss) Available to Common Stockholders, Basic Debt Instrument Redemption [Table] Debt Instrument Redemption [Table] Secured borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Loans held for investment, net of allowance for loan losses Loans Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Gain on sale of fixed assets Gain on building sale Gain (Loss) on Disposition of Property Plant Equipment Non- Controlling Interest Noncontrolling Interest [Member] Investment securities with fair value Financial Instruments, Owned, at Fair Value Shares outstanding (in shares) Weighted Average Number of Shares Issued, Basic Amortization of debt issuance cost Amortization of Debt Issuance Costs Tier 2 Capital Tier 2 Capital The amount of tier 2 capital. Long-term debt, net of issuance costs Recorded Value Long-term debt Long-Term Debt Loan servicing income, net of amortization Loan servicing income, net of amortization The amount of loan servicing fees net of amortization. Term loan balance for 2024/2023 Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year FHLB, Advances, Term Federal Home Loan Bank, Advances, Term [Member] Federal Home Loan Bank, Advances, Term Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Regulatory assets Regulatory Asset Fair Value, HTM, More than Five Years to Ten Years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Security Exchange Name Security Exchange Name Held to maturity (fair value of $3,803 and $4,103 at September 30, 2026 and December 31, 2025) Amortized Cost Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss Amortized Cost, HTM, Total Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Financing receivable, before allowance for credit loss Financing Receivable, before Allowance for Credit Loss Loans modified to borrowers experiencing financial difficulty Financing Receivable, Excluding Accrued Interest, Modified, Subsequent Default Total Risk-Based Capital Ratio Banking Regulation, Total Capital [Abstract] Time Deposit Maturities, After Year Four Time Deposit Maturities, After Year Four Time Deposit Maturities, After Year Four Accrued interest and other assets Total accrued interest and other assets Interest Receivable and Other Assets Fair Value, AFS, Twelve Months or More Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Name Outstanding Recovery, Individual Name Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Other grant income Government Assistance, Award Amount Interest-earning time deposits in other financial institutions Interest-earning time deposits in other financial institutions For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing time deposits in other financial institutions. Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Commercial Real Estate Commercial Real Estate Collateral [Member] Relating to commercial real estate collateral. Fair Value, HTM, One Year or Less Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Time deposits Interest Expense, Time Deposits PGBH Trust PGB Holdings Inc And Banking Subsidiary Pacific Global Bank [Member] Represents information related to PGB Holdings Inc and Banking Subsidiary Pacific Global Bank. Schedule of Maturities of Time Deposits Time Deposit Maturities [Table Text Block] Principal Amount Long-Term Debt, Gross Deposit Liability [Table] Deposit Liability [Table] Number of Issuances, HTM, Less than Twelve Months Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, Less Than 12 Months, Number of Positions 1 Number of investments in debt securities held-to-maturity, in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset. Asset Class [Domain] Asset Class [Domain] Repayments of FHLB advances Payments of FHLBank Borrowings, Financing Activities Related Party Transactions [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Diluted (in shares) Used in dilutive EPS (in shares) Weighted Average Number of Shares Outstanding, Diluted Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Entity Emerging Growth Company Entity Emerging Growth Company Related Party Transaction [Line Items] Related Party Transaction [Line Items] Mortgage loans in the process of foreclosure Mortgage Loans in Process of Foreclosure, Amount Loans held for investment, excluding allowance for loan losses Total Loans HFI Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss Underlying Security Market Price Change Underlying Security Market Price Change, Percent Commercial paper Commercial Paper [Member] Gross Unrealized Losses Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss Less: amount of payment representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Collateralized deposits from the State of California Collateralized Deposits From the State of California [Member] Represents Collateralized Deposits From the State of California. Prepaid assets Prepaid Expense Savings deposits, NOW and money market accounts Interest Expense, NOW Accounts, Money Market Accounts, and Savings Deposits Revenue from Contract with Customer [Abstract] To Be Well-Capitalized Under Prompt Corrective Action Provisions, ratio CapitalRequiredForCapitalConversationBufferFullyPhasedInToRiskWeightedAssets Represents capital required for capital conversation buffer fully phased in to risk weighted assets. Intangible Asset, Goodwill and Other [Abstract] To Be Well-Capitalized Under Prompt Corrective Action Provisions, ratio Tier One Leverage Capital Required Plus Capital Conservation Buffer Fully Phased In Average Assets Represents tier one leverage capital required plus capital conservation buffer fully phased in average assets. Actual Banking Regulation, Common Equity Tier 1 Risk-Based Capital, Actual Total future minimum lease payments Lessee, Operating Lease, Liability, to be Paid Transfers and Servicing [Abstract] Derivative assets, notional amount Derivative Asset, Notional Amount Proceeds from loans sold Proceeds from Sale, Loan, Held-for-Sale YTD gross charge-offs, 2024/2023 Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff Collateral Held [Domain] Collateral Held [Domain] Outstanding, beginning balance (in dollars per share) Outstanding, ending balance (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value All Executive Categories All Executive Categories [Member] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Federal Reserve Bank of San Francisco Secured Line of Credit Federal Reserve Bank of San Francisco Secured Line of Credit [Member] Represents information related to Federal Reserve Bank of San Francisco secured line of credit. Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Net increase in demand deposits and savings accounts Net increase in demand deposits and savings accounts The increase (decrease) during the period in demand deposits and savings accounts. Data processing Information Technology and Data Processing Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Debt Disclosure [Abstract] SEGMENT INFORMATION Segment Reporting [Text Block] Maturities, repayments and calls Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale Minimum Minimum [Member] Investment Type [Axis] Investment Type [Axis] Provision for credit losses rbb_ProvisionForCreditLossesExpensed The amount of provision for credit losses expensed. Amortization Servicing Asset at Amortized Cost, Amortization Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Amortization of investment in affordable housing tax credits Investment Program, Proportional Amortization Method, Applied, Amortization Expense Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Outstanding, weighted-average remaining contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted-Average Remaining Contractual Term Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] FHLB advances Advance from Federal Home Loan Bank Other income Noninterest Income, Other Operating Income Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Estimated useful life (in years) Intangible Asset, Finite-Lived, Useful Life Fair Value, AFS, More than Ten Years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Exercise Price Award Exercise Price Restricted stock units vested Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures On a recurring basis: Fair Value, Recurring [Member] Share repurchase program, authorized, amount Share Repurchase Program, Authorized, Amount Segment Reporting Information [Line Items] Segment Reporting [Line Items] Document Quarterly Report Document Quarterly Report Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Lender Name [Axis] Lender Name [Axis] Special mention Special Mention [Member] REGULATORY MATTERS Regulatory Capital Requirements under Banking Regulations [Text Block] YTD gross charge-offs, 2023/2022 Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff Sales of investment securities Proceeds from Sale of Debt Securities, Available-for-Sale Deposits Deposits [Member] Regulatory Assets and Liabilities Disclosure [Abstract] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Equity Component [Domain] Equity Component [Domain] Measurement Input Type [Domain] Measurement Input Type [Domain] Loans, net Loans Receivable, Fair Value Disclosure Adoption Date Trading Arrangement Adoption Date Subordinated debentures Subordinated Debt Obligations, Fair Value Disclosure Servicing asset Servicing assets Servicing Asset Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Accounting Policies [Abstract] Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Lease liabilities - operating leases Total present value of lease payments Lease liabilities Operating Lease, Liability Beginning balance (in shares) Ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Fair Value Fair Value, HTM, Total Investment securities – HTM Debt Securities, Held-to-Maturity, Fair Value REPURCHASE OF COMMON STOCK Treasury Stock [Text Block] Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Commercial: Commercial Portfolio Segment [Member] CMO: Residential Residential Collateralized Mortgage Obligations [Member] Related to residential collateralized mortgage obligations. Share repurchase program, authorized shares (in shares) Share Repurchase Program, Authorized, Number of Shares Advance With One Time Call, Nine Month Lock Out, Two Advance With One Time Call, Nine Month Lock Out, Two [Member] Advance With One Time Call, Nine Month Lock Out, Two Unfunded commitments Investment Program, Proportional Amortization Method, Elected, Commitment Accrued interest receivable Interest Receivable Fair Value Disclosure Fair value portion of interest earned but not received. Percentage of outstanding stock maximum Share-Based Compensation Arrangement by Share-Based Payment Award, Percentage of Outstanding Stock Maximum Business Combination [Domain] Business Combination [Domain] Schedule of Amortized Cost Basis of by Collateral -Dependent Loans Schedule of Financing Receivables by Collateral Held [Table Text Block] Tabular disclosure of financing receivables by collateral held. Time Deposit, FDIC Insurance Limit [Axis] Time Deposit, FDIC Insurance Limit [Axis] Time Deposit, FDIC Insurance Limit Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Operating lease, rental income Operating Lease, Lease Income Financial Asset, Aging [Domain] Financial Asset, Aging [Domain] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] All Adjustments to Compensation All Adjustments to Compensation [Member] Other items Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item Business Combination [Axis] Business Combination [Axis] Core deposits Core Deposits [Member] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Substandard Substandard [Member] Pledging Purpose [Domain] Pledging Purpose [Domain] Interest-earning deposits Interest Income, Deposits with Financial Institutions Income Statement [Abstract] Income Statement [Abstract] Document Transition Report Document Transition Report Minimum Required for Capital Adequacy Purposes Banking Regulation, Tier 1 Leverage Capital, Capital Adequacy, Minimum Net deferred tax assets Deferred Income Tax Assets, Net Outstanding loan commitments Unfunded Loan Commitments Available To Related Parties Represents available to related parties for unfunded loan commitments. Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Other Commitments [Domain] Other Commitments [Domain] City Area Code City Area Code Allowance for Credit Loss [Abstract] SUBSEQUENT EVENTS Subsequent Events [Text Block] Amortization of right-of-use asset Operating Lease, Right-of-Use Asset, Periodic Reduction Name Forgone Recovery, Individual Name Total Loans rbb_LoansHeldForInvestmentAndHeldForSaleGross The total carrying amount of loans held for investment, and loans held for sale before allowance of loan losses. Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Weighted-Average Grant Date Fair Value Per Share Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Impairment losses Investment Program, Proportional Amortization Method, Elected, Impairment Loss Wholesale time deposits Deposits, Wholesale Total interest and dividend income Interest and dividend income Interest and Dividend Income, Operating Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Loans held for sale Loan, Mortgage, Held-for-Sale, Fair Value Disclosure Interest Receivable and Other Assets [Abstract] FRB Secured Line of Credit Federal Home Loan Bank of San Francisco Secured Line of Credit [Member] Represents information related to Federal Home Loan Bank of San Francisco secured line of credit. BUSINESS DESCRIPTION Nature of Operations [Text Block] Cash surrender value of bank owned life insurance (BOLI) Cash Surrender Value of Life Insurance Compensation expense Share-Based Payment Arrangement, Expense Number of Issuances, AFS, Twelve Months or More Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Measurement Basis [Axis] Measurement Basis [Axis] Repurchase of common stock (in shares) Stock Repurchased and Retired During Period, Shares 30-89 Days Past Due Financial Asset, 30 to 89 Days Past Due [Member] Financial asset more than 29 days past due but fewer than 90 days past due. Advance with No Call Advance with No Call [Member] Advance with No Call Stock options exercised (in shares) Exercised (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Purchase of other equity securities, net rbb_PaymentsToAcquireProceedsFromOtherInvestments The amount of cash outflow (inflow) from other investments. Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Unrealized (loss)/gain on securities available for sale OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax Actual, ratio Banking Regulation, Tier 1 Risk-Based Capital Ratio, Actual Fair Value, AFS, One Year or Less Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Subsequent Event Type [Domain] Subsequent Event Type [Domain] To Be Well-Capitalized Under Prompt Corrective Action Provisions, ratio Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio Represents equity tier one capital required plus capital conversation buffer fully phased in to risk weighted assets. Forfeited/cancelled (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value YTD gross charge-offs, Revolving Financing Receivable, Excluding Accrued Interest, Revolving, Writeoff Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Forfeited/cancelled (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period Schedule of Measurement Inputs and Valuation Techniques Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] 2029 Time Deposit Maturities, Year Three Entity Current Reporting Status Entity Current Reporting Status Net cash provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Bank Royal Business Bank [Member] Represents information related to Royal Business Bank. Single Reportable Segment Single Reportable Segment [Member] Single Reportable Segment Commercial real estate Commerical Real Estate Loans [Member] Represents information related to commercial real estate loans. Adjustments to reconcile net income to net cash from operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Number of Issuances, HTM, Twelve Months or More Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions 1 Number of investments in debt securities held-to-maturity, in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset. Financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Premises and equipment, net Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Other revenues Other Interest and Dividend Income Minimum Required for Capital Adequacy Purposes, ratio CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets Represents common equity tier one risk based capital required for capital adequacy to risk weighted assets. Financial Instruments [Domain] Financial Instruments [Domain] Term loan balance for 2022/2021 Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year Derivative assets, fair value Derivative Asset Forward mortgage loan sale contracts Forward Mortgage Loan Sale Contracts [Member] Represents forward mortgage loan sale contracts. Intangible Asset, Finite-Lived, Class [Axis] Intangible Asset, Finite-Lived, Class [Axis] Stock options exercised Stock Issued During Period, Value, Stock Options Exercised GOODWILL AND INTANGIBLES Intangible Asset and Goodwill [Text Block] Underlying Securities Award Underlying Securities Amount Fair Value Estimate of Fair Value Measurement [Member] REVENUE FROM CONTRACTS WITH CUSTOMERS Revenue from Contract with Customer [Text Block] Combination - Rate Reduction and Term Modification Extended Maturity and Interest Rate Reduction [Member] Forfeited/cancelled (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Other investing activities, net Payment for (Proceeds from) Other Investing Activity Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Segment Reporting [Table] Segment Reporting [Table] Number of shares available for grant (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Related Party Transaction [Table] Related Party Transaction [Table] Total Loan Modifications Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount Provision for credit losses Provision for credit losses Provision for Loan, Lease, and Other Losses Time deposits over $250,000 Time Deposits, at or Above FDIC Insurance Limit Schedule of Operating Lease Lease, Cost [Table Text Block] Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Fair Value, AFS, Less than Twelve Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Schedule of Financial Assets and Liabilities Measured at Fair Value Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Current Fiscal Year End Date Current Fiscal Year End Date Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Provision for/(reversal of) credit losses Financing Receivable, Excluding Accrued Interest, Credit Loss Expense (Reversal) Loans serviced for others Loans serviced for others Represent amount of loans serviced for others. Servicing Asset at Amortized Cost, Balance [Roll Forward] Servicing Asset at Amortized Cost, Balance [Roll Forward] Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Cash dividends on common stock (in dollars per share) Dividends declared (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity File Number Entity File Number Other real estate owned Other Real Estate Owned [Member] Represents information related to other real estate owned. Schedule of Amortized Cost and Fair Value of Investment Securities Portfolio Investments Classified by Contractual Maturity Date [Table Text Block] Weighted-Average Exercise Price Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Time deposits held through the CDARS program Certificates Of Deposit Held Through Cdars [Member] Represents Certificates of Deposit Held Through CDARS. Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Principal Officers, Directors and their Affiliates Principal Officers, Directors and their Affiliates [Member] Represents information related to principal officers, directors and their affiliates. Measure: Measure [Axis] Equity Components [Axis] Equity Components [Axis] Taxes paid Income Tax Paid, after Refund Received Entity Interactive Data Current Entity Interactive Data Current Variable Rate [Axis] Variable Rate [Axis] Number of Issuances, HTM, Total Debt Securities, Held-to-Maturity, Unrealized Loss Position, Number of Positions 1 Number of investments in debt securities held-to-maturity, in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Amortized Cost, AFS, More than One Year to Five Years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Entity Small Business Entity Small Business Unamortized Valuation Reserve Debt Instrument, Unamortized Discount Net interest income before provision for credit losses Interest Income (Expense), Operating MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] SUBORDINATED DEBENTURES Subordinated Borrowings Disclosure [Text Block] Document Type Document Type Debt instrument, repurchase face amount Debt Instrument, Repurchased Face Amount Fair Value, HTM, More than Ten Years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Debt Instrument, Redemption [Line Items] Debt Instrument, Redemption [Line Items] Allowance for credit losses Allowance for Credit Loss and Unfunded Loan Commitments [Member] Represents allowance for credit loss and unfunded loan commitments. Debt securities, AFS, allowance for credit loss Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest Advance With One Time Call, Three Month Lock Out, Two Advance With One Time Call, Three Month Lock Out, Two [Member] Advance With One Time Call, Three Month Lock Out, Two Actual, ratio Banking Regulation, Tier 1 Leverage Capital Ratio, Actual Exercisable, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Subsequent Event [Line Items] Subsequent Event [Line Items] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Local Phone Number Local Phone Number Pledged Status [Domain] Pledged Status [Domain] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Commitments and contingencies - Note 13 Commitments and Contingencies Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] 2030 Intangible Asset, Finite-Lived, Estimated Amortization Expense, Year Four Executive Category: Executive Category [Axis] Schedule of Restricted Stock Units Activity Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Liabilities and Shareholders’ Equity Liabilities and Equity [Abstract] Other Commitments [Table] Other Commitments [Table] Measurement input Loan, Held-for-Sale, Measurement Input Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Gain on sale of loans Gain on sale of loans Gain (Loss) on Sales of Loans, Net SBA SBA Loans [Member] Represents information related to SBA loans. Supplemental disclosure of cash flow information Supplemental Cash Flow Information [Abstract] FHLB, Overnight Advances Federal Home Loan Bank Overnight Advances [Member] Overnight borrowings from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and also in times of liquidity shortages. The member institution executes a promissory note, which is generally collateralized by government securities to the Federal Reserve or loans. PEO Name PEO Name Other segment items Segment Reporting, Other Segment Item, Amount Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Cash and due from banks Cash and Due from Banks Schedule of Investment in Past Due Loans HFI, by Loan Segment and Class Financing Receivable, Past Due [Table Text Block] Investment securities Interest and Dividend Income, Securities, Operating Current Financial Asset, Not Past Due [Member] Other Commitments [Line Items] Other Commitments [Line Items] Exercised (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Legal and professional Legal and professional The amount of expense (reversal of expense) in the period for legal and professional fees incurred on or before the balance sheet date. Federal Home Loan Bank, Advances, Option [Axis] Federal Home Loan Bank, Advances, Option [Axis] Increase in cash surrender value of BOLI Bank Owned Life Insurance Income Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Total comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Measurement Frequency [Domain] Measurement Frequency [Domain] Debt Instrument [Axis] Debt Instrument [Axis] Subsequent Event [Table] Subsequent Event [Table] Stock-based compensation, net Share-Based Payment Arrangement, Noncash Expense Interest expense: Interest Expense, Operating and Nonoperating [Abstract] Salaries and employee benefits Salaries and benefits expense Labor and Related Expense Schedule of Subordinated Debentures Schedule of Subordinated Debentures [Table Text Block] Tabular disclosure of subordinated debentures. Maturities, repayments and calls Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities Basic (in dollars per share) Basic earnings per common share (in dollars per share) Earnings Per Share, Basic Measurement Input Type [Axis] Measurement Input Type [Axis] Insider Trading Arrangements [Line Items] Number of fair value unvested shares (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Nonvested, Number of Shares Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Recoveries Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Recovery Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] SBA Small Business Administration Loans [Member] Represents information related to small business administration loan. Cover [Abstract] Cover [Abstract] Consolidated RbbBancorp [Member] Represents information related to RBB Bancorp. YTD gross charge-offs, 2025/2024 Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff Equity Awards Adjustments Equity Awards Adjustments [Member] Prepayment speed Measurement Input, Prepayment Rate [Member] YTD gross charge-offs, Revolving Converted to Term During the Period Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff Pass Pass [Member] Plan Name [Axis] Plan Name [Axis] Schedule of Loan Held for Investment ("HFI") Portfolio by Loan Segment and Class Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Accrued interest receivable on loans rbb_LoansReceivableInterest The amount of interest on loans receivable. LONG-TERM DEBT Long-Term Debt [Text Block] Tenor Spread Adjustment Tenor Spread Adjustment [Member] Represents the tenor spread adjustment. Shareholders' equity: Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Forfeited/cancelled (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Fair Value, HTM, Twelve Months or More Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value 1 Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer. Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized MBS: Commercial Commercial Mortgage-Backed Securities [Member] FHLB, Advances, Putable Option Federal Home Loan Bank, Advances, Putable Option [Member] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Combination - Principal Reduction, Rate Reduction and Term Modification Principal Reduction, Extended Maturity, and Interest Rate Reduction [Member] Loan modification for extension of term of loan in which it must be paid, reduction of contractual interest rate, reduction of interest rate to lower than current market rate for new debt with similar risk, and reduction in principal. Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other commitment Other Commitment Total consolidated revenues rbb_InterestAndDividendIncomeOperatingAndNonoperating Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein. Aggregate Available Trading Arrangement, Securities Aggregate Available Amount INCOME TAXES Income Tax Disclosure [Text Block] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Table] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Table] Tax credits from LIHTC investments Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization Expense Entity Filer Category Entity Filer Category Fair Value, AFS, Total Debt Securities, Available-for-Sale, Unrealized Loss Position Director Director [Member] Financing Receivable, Nonaccrual [Line Items] Financing Receivable, Nonaccrual [Line Items] Time Deposit, FDIC Insurance Limit [Domain] Time Deposit, FDIC Insurance Limit [Domain] Time Deposit, FDIC Insurance Limit [Domain] Financial Asset, Aging [Axis] Financial Asset, Aging [Axis] Investments, Debt and Equity Securities [Abstract] Deposits: Deposits [Abstract] Schedule of Fair Value and Gross Unrealized Losses of Our Investment Securities Gain (Loss) on Securities [Table Text Block] Net income Net income Consolidated net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Government Assistance, Type [Domain] Government Assistance, Type [Domain] Entity Address, Address Line One Entity Address, Address Line One Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Income tax expense Income tax expense Income Tax Expense (Benefit) Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Charge-offs YTD gross charge-offs, Total Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Common stock reserved of issued and outstanding (as a percent) Share Based Compensation Arrangement By Share Based Payment, Award Common Stock Reserved As Percentage Of Issued And Outstanding Represents percentage of issued and outstanding for share based compensation by share based payment. Recognition of operating lease right-of-use assets Recognition of operating lease right-of-use assets Represents amount of operating lease right-of-use assets recognized during the period. Loan Restructuring Modification [Domain] Loan Restructuring Modification [Domain] Schedule of Stock Options Awards and Activity Share-Based Payment Arrangement, Option and Stock Appreciation Rights, Activity [Table Text Block] Statement [Table] Statement [Table] Exercise of stock options Proceeds from Stock Options Exercised Term loan balance for 2025/2024 Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year Schedule of Loans HFI on Nonaccrual Status Financing Receivable, Nonaccrual [Table Text Block] Net accretion of securities, loans, deposits, and other rbb_NetAccretionOfSecuritiesLoansDepositsAndOther The amount of net accretion of securities, loans, deposits, and other investments. Directors and Their Affiliates Directors and Their Affiliates [Member] Represents directors and their affiliates. BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Significant Accounting Policies [Text Block]