Label	Element	Value
Prospectus [Line Items]	rr_ProspectusLineItems
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Entity Registrant Name	dei_EntityRegistrantName	RBB FUND, INC.
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Motley Fool \| Motley Fool 100 Index ETF
Prospectus [Line Items]	rr_ProspectusLineItems
Risk/Return [Heading]	rr_RiskReturnHeading	Motley Fool 100 Index ETF Summary Section
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Motley Fool 100 Index ETF (the "Fool 100 Fund") seeks investment results that correspond (before fees and expenses) generally to the total return performance of the Motley Fool 100 Index (the "Fool 100 Index" – for more on this, see the "Principal Investment Strategies" section).
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fool 100 Fund ("Shares"). This table and the Example below do not include the brokerage commissions that investors may pay on their purchases and sales of Fund Shares.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fool 100 Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fool 100 Fund Shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fool 100 Fund's performance. For the fiscal year ended August 31, 2019, the Fool 100 Fund's portfolio turnover rate was 26% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	26.00%
Expense Exchange Traded Fund Commissions [Text]	rr_ExpenseExchangeTradedFundCommissions	This table and the Example below do not include the brokerage commissions that investors may pay on their purchases and sales of Fund Shares.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fool 100 Fund with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Fool 100 Fund for the time periods indicated and then redeem all of your Shares at the end of those periods. The Example also assumes that: (1) your investment has a 5% return each year, and (2) the Fool 100 Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fool 100 Fund is an exchange-traded fund ("ETF") and employs a "passive management" – or indexing – investment approach designed to track the total return performance, before fees and expenses, of the Fool 100 Index. Motley Fool Asset Management, LLC (the "Adviser" or "MFAM") serves as the investment adviser to the Fool 100 Fund . The Fool 100 Index was developed by The Motley Fool, LLC ("The Motley Fool"), an affiliate of the Adviser. The Motley Fool 100 Index The Fool 100 Index was established by The Motley Fool in 2017 and is a proprietary, rules-based index designed to track the performance of the 100 largest, most liquid U.S. companies that have been recommended by The Motley Fool's analysts and newsletters. To be eligible for inclusion in the Fool 100 Index, a company must be among the 100 largest domestic firms by market capitalization in The Motley Fool's "recommendation universe." That recommendation universe includes all companies domiciled in the United States that are either active recommendations of a newsletter published by The Motley Fool or are among the 150 highest rated U.S. companies in The Motley Fool's analyst opinion database. Each of the 100 largest company's share of the Fool 100 Index (or "weighting") is set to equal the company's share of all Index companies' aggregate market value. The Fool 100 Index is reconstituted and rebalanced quarterly. From time to time, the Fool 100 Index may include more or less than 100 companies as a result of events such as acquisitions, spin-offs and other corporate actions. The Fool 100 Index is calculated and administered by Solactive AG (the "Index Calculation Agent"), which is not affiliated with the Fool 100 Fund, the Adviser or The Motley Fool. Additional information regarding the Fool 100 Index, including its value, is available on the websites of the Fool 100 Index at www.fool100.com and the Index Calculation Agent, at www.solactive.com. The Fool 100 Fund's Investment Strategy Under normal circumstances, at least 80% of the Fool 100 Fund's total assets (exclusive of any collateral held from securities lending) will be invested in the component securities of the Fool 100 Index. The Adviser expects that, over time, if it has sufficient assets, the correlation between the Fool 100 Fund's performance and that of the Fool 100 Index, before fees and expenses, will be 95% or better. The Fool 100 Fund will generally use a "replication" strategy to achieve its investment objective, meaning it generally will invest in all of the component securities of the Fool 100 Index. However, the Fool 100 Fund may use a "representative sampling" strategy, meaning it may invest in a sample of the securities in the Fool 100 Index whose risk, return and other characteristics closely resemble the risk, return and other characteristics of the Fool 100 Index as a whole, when the Adviser believes it is in the best interests of the Fool 100 Fund (e.g., when replicating the Fool 100 Index involves practical difficulties or substantial costs, a Fool 100 Index constituent becomes temporarily illiquid, unavailable or less liquid, or as a result of legal restrictions or limitations that apply to the Fool 100 Fund but not to the Fool 100 Index). The Fool 100 Fund generally may invest up to 20% of its total assets (exclusive of any collateral held from securities lending) in securities or other investments not included in the Fool 100 Index, but which the Adviser believes will help the Fool 100 Fund track the Fool 100 Index. For example, the Fool 100 Fund may invest in securities that are not components of the Fool 100 Index to reflect various corporate actions and other changes to the Fool 100 Index (such as reconstitutions, additions and deletions). The Fool 100 Fund is non-diversified for the purposes of the Investment Company Act of 1940, as amended ("1940 Act"), which means that the Fool 100 Fund may invest in fewer securities at any one time than a diversified fund. To the extent the Fool 100 Index concentrates (i.e., holds more than 25% of its total assets) in the securities of a particular industry, the Fool 100 Fund will concentrate its investments to approximately the same extent as the Fool 100 Index. As of August 31, 2019, securities in the information technology, communication services and consumer discretionary sectors represented a significant portion of the Fool 100 Index. The Fool 100 Fund may also seek to increase its income by lending securities. The Fool 100 Fund has elected to be, and intends to continue to qualify each year for treatment as a regulated investment company ("RIC") under Subchapter M of Subtitle A, Chapter 1, of the Internal Revenue Code of 1986, as amended (the "Code").
Risk [Heading]	rr_RiskHeading	Principal Investment Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The value of the Fool 100 Fund's investments may decrease, which will cause the value of the Fool 100 Fund's Shares to decrease. As a result, you may lose money on your investment in the Fool 100 Fund, and there can be no assurance that the Fool 100 Fund will achieve its investment objective. The Fool 100 Fund's principal risks are presented in alphabetical order to facilitate finding particular risks and comparing them with other funds. Each risk summarized below is considered a "principal risk" of investing in the Fool 100 Fund, regardless of the order in which it appears. Different risks may be more significant at different times depending on market conditions or other factors. ● Authorized Participants, Market Makers and Liquidity Providers Concentration Risk. The Fool 100 Fund has a limited number of financial institutions that are institutional investors and may act as authorized participants ("APs"). In addition, there may be a limited number of market makers and/or liquidity providers in the marketplace. To the extent either of the following events occur, Fool 100 Fund Shares may trade at a material discount to net asset value ("NAV") and possibly face delisting: (i) APs exit the business or otherwise become unable to process creation and/or redemption orders and no other APs step forward to perform these services, or (ii) market makers and/or liquidity providers exit the business or significantly reduce their business activities and no other entities step forward to perform their functions. ● Cyber Security Risk. Cyber security risk is the risk of an unauthorized breach and access to the Fool 100 Fund's assets, Fund or customer data (including private shareholder information), or proprietary information, or the risk of an incident occurring that causes the Fool 100 Fund, the Adviser, custodian, transfer agent, distributor and other service providers and financial intermediaries to suffer data breaches, data corruption or lose operational functionality or prevent the Fool 100 Fund's investors from purchasing, redeeming or exchanging shares or receiving distributions. The Fool 100 Fund and the Adviser have limited ability to prevent or mitigate cyber security incidents affecting third-party service providers. Successful cyber-attacks or other cyber-failures or events affecting the Fool 100 Fund or its service providers may adversely impact and cause financial losses to the Fool 100 Fund or its shareholders. ● Equity Markets Risk. The equity securities held in the Fool 100 Fund's portfolio may experience sudden, unpredictable drops in value or long periods of decline in value. This may occur because of factors that affect securities markets generally or factors affecting specific issuers, industries, or sectors in which the Fool 100 Fund invests. Common stocks are generally exposed to greater risk than other types of securities, such as preferred stocks and debt obligations, because common stockholders generally have inferior rights to receive payment from issuers. ● Index Rankings and Methodology Risk. The Fool 100 Index is comprised of the 100 largest U.S. companies that are either active recommendations of The Motley Fool LLC's newsletter or are among the 150 highest rated U.S. companies in The Motley Fool LLC's analyst opinion database, and are weighted based on their market value relative to the total market value of other companies in the Fool 100 Index. Factors used by The Motley Fool LLC's analysts in their qualitative and quantitative analysis of companies included in the Fool 100 Index, and the weight placed on those factors, may not be predictive of a security's value and, thus, have an adverse effect on the Fool 100 Fund. In addition, changes in The Motley Fool LLC's recommendations or rankings methodologies may have an adverse effect on the Fool 100 Fund. Factors that affect a security's value can change over time, and these changes may not be reflected in the Fool 100 Index methodology. Moreover, the methodology and the calculation of the Fool 100 Index could be subject to errors. If the composition of the Fool 100 Index reflects such errors, the Fool 100 Fund's portfolio can be expected to reflect the errors, too. ● Large-Capitalization Investing. The securities of large-capitalization companies may be relatively mature compared to smaller companies and therefore subject to slower growth during times of economic expansion. ● Market Risk. The trading prices of equity securities and other instruments fluctuate in response to a variety of factors. The Fool 100 Fund's NAV and market price may fluctuate significantly in response to these and other factors. As a result, an investor could lose money over short or long periods of time. ● Non-Diversification Risk. The Fool 100 Fund is non-diversified, which means that it may invest a high percentage of its assets in a limited number of securities. Since the Fool 100 Fund is non-diversified, its NAV, market price and total returns may fluctuate or fall more than a diversified fund. Gains or losses on a single stock may have a greater impact on the Fool 100 Fund. ● Passive Investment Risk. The Fool 100 Fund is not actively managed and the Adviser does not attempt to take defensive positions in any market conditions, including adverse markets. The Fool 100 Fund and its Adviser will not sell shares of an equity security due to current or projected underperformance of a security, industry, or sector, unless that security is removed from the Fool 100 Index or the selling of shares of that security is otherwise required upon a reconstitution of the Fool 100 Index as addressed in the Index methodology. ● Portfolio Turnover Risk. In seeking to replicate the Fool 100 Index, which is adjusted and rebalanced quarterly, the Fool 100 Fund may incur relatively high portfolio turnover. High portfolio turnover may result in increased transaction costs and may lower Fund performance. ● Secondary Market Trading Risk. Although Shares are listed on a national securities exchange, the Exchange, and may be traded on U.S. exchanges other than the Exchange, there can be no assurance that an active or liquid trading market for them will develop or be maintained. In addition, trading in Shares on the Exchange may be halted. ● Sector Risk. To the extent the Fool 100 Fund invests more heavily in particular sectors of the economy, its performance will be especially sensitive to developments that significantly affect those sectors. ● Communication Services Sector Risk. Companies in the communications sector may be affected by industry competition, substantial capital requirements, government regulation, cyclicality of revenues and earnings, obsolescence of communications products and services due to technological advancement, a potential decrease in the discretionary income of targeted individuals and changing consumer tastes and interests. ● Consumer Discretionary Sector Risk. Companies in the consumer discretionary sector can be significantly affected by the performance of the overall economy, interest rates, competition, consumer confidence and spending, and changes in demographics and consumer tastes. ● Information Technology Sector Risk. In addition to market or economic factors, companies in the information technology sector and companies that rely heavily on technology are particularly vulnerable to rapid changes in technology product cycles, rapid product obsolescence, government regulation and competition. ● Securities Lending Risk. The Fool 100 Fund may lend portfolio securities to institutions, such as certain broker- dealers. The Fool 100 Fund may experience a loss or delay in the recovery of its securities if the borrowing institution breaches its agreement with the Fund. ● Shares May Trade at Prices Other Than NAV. As with all ETFs, Shares may be bought and sold in the secondary market at market prices. Although it is expected that the market price of Shares will approximate the Fool 100 Fund's NAV, there may be times when the market price of Shares is more than the NAV intra-day (premium) or less than the NAV intra-day (discount). This risk is heightened in times of market volatility or periods of steep market declines. ● Tracking Error Risk. As with all index funds, the performance of the Fool 100 Fund and its Index may differ from each other for a variety of reasons. For example, the Fool 100 Fund incurs operating expenses and portfolio transaction costs not incurred by the Fool 100 Index. In addition, the Fool 100 Fund may not be fully invested in the securities of the Fool 100 Index at all times or may hold securities not included in the Fool 100 Index.
Risk Lose Money [Text]	rr_RiskLoseMoney	As a result, you may lose money on your investment in the Fool 100 Fund, and there can be no assurance that the Fool 100 Fund will achieve its investment objective.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	The Fool 100 Fund is non-diversified, which means that it may invest a high percentage of its assets in a limited number of securities. Since the Fool 100 Fund is non-diversified, its NAV, market price and total returns may fluctuate or fall more than a diversified fund. Gains or losses on a single stock may have a greater impact on the Fool 100 Fund.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information:
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	Performance information for the Fool 100 Fund is not included because the Fool 100 Fund did not have one full calendar year of performance prior to the date of this Prospectus. Performance information will be available in the Prospectus once the Fool 100 Fund has at least one calendar year of performance. Updated performance information is available at www.mfamfunds.com/resources or by calling the Fool 100 Fund toll free at 1-800-617-0004.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance information for the Fool 100 Fund is not included because the Fool 100 Fund did not have one full calendar year of performance prior to the date of this Prospectus.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-617-0004
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.mfamfunds.com/resources
Motley Fool \| Motley Fool 100 Index ETF \| Motley Fool 100 Index ETF Shares
Prospectus [Line Items]	rr_ProspectusLineItems
Trading Symbol	dei_TradingSymbol	TMFC
Management Fees	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	none
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.50%
One Year	rr_ExpenseExampleYear01	$ 51
Three Years	rr_ExpenseExampleYear03	160
Five Years	rr_ExpenseExampleYear05	280
Ten Years	rr_ExpenseExampleYear10	$ 628

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Risk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.

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Total Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."

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Management Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."

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Investment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).

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Investment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).

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Annual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investment)

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"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.

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If applicable, include a statement explaining that updated performance information is available and providing a Web site address and/or toll-free (or collect) telephone number where the updated information may be obtained.

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Risk/Return Bar Chart and Table.

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Disclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.

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This element represents the rate of portfolio turnover presented as a percentage (SEC Form N-1A 2006-09-14 A.3.example.3 Portfolio Turnover A.3.instructions.5 Portfolio Turnover).

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The date of the prospectus.

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Narrative Risk Disclosure.

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Summarize the principal risks of investing in the Fund, including the risks to which the Fund's portfolio as a whole is subject and the circumstances reasonably likely to affect adversely the Fund's net asset value, yield, and total return. Unless the Fund is a Money Market Fund, disclose that loss of money is a risk of investing in the Fund. If the Fund is a Money Market Fund, include the following statement: "You could lose money by investing in the Fund."

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Narrative Risk Disclosure. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.

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If applicable, state that the Fund is non-diversified, describe the effect of non-diversification (e.g., disclose that, compared with other funds, the Fund may invest a greater percentage of its assets in a particular issuer), and summarize the risks of investing in a non-diversified fund.

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Risk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicated

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Principal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.

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