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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Aug. 31, 2019
Entity Registrant Name dei_EntityRegistrantName RBB FUND, INC.
Entity Central Index Key dei_EntityCentralIndexKey 0000831114
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Dec. 20, 2019
Document Effective Date dei_DocumentEffectiveDate Dec. 31, 2019
Prospectus Date rr_ProspectusDate Dec. 31, 2019
Boston Partners Institutional | Boston Partners All-Cap Value Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading SUMMARY SECTION — BOSTON PARTNERS ALL-CAP VALUE FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks to provide long-term growth of capital primarily through investment in equity securities.

Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

Current income is a secondary objective.

Expense [Heading] rr_ExpenseHeading Expenses and Fees
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy, hold, and sell Institutional Class shares of the Fund. You may be required to pay commissions and/or other forms of compensation to a broker for transactions in Institutional Class shares of the Fund, which are not reflected in the tables or the examples below.

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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2021
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The 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 Fund shares are held in a taxable account. These costs, which are not reflected in Total annual Fund operating expenses or in the Example, affect the Fund's performance. During the fiscal year ended August 31, 2019, the portfolio turnover rate for the Fund was 33% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 33.00%
Expense Exchange Traded Fund Commissions [Text] rr_ExpenseExchangeTradedFundCommissions You may be required to pay commissions and/or other forms of compensation to a broker for transactions in Institutional Class shares of the Fund, which are not reflected in the tables or the examples below.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees Please note that the amount of Total annual Fund operating expenses and Total annual Fund operating expenses after fee waiver and/or expense reimbursement shown in the above table will differ from the “Financial Highlights” section of the prospectus, which reflects the operating expenses of the Fund and does not include indirect expenses such as acquired fund fees and expenses.
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 Fund with the cost of investing in other mutual funds. The Example assumes that you invest $100,000 in the Fund for the time periods indicated and that you sell all of your shares at the end of the period. The Example also assumes that your investment has a 5% return each year and that the operating expenses of the Fund remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Strategy [Heading] rr_StrategyHeading Summary of Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its objective by investing, under normal circumstances, at least 80% of its net assets (including borrowings for investment purposes) in a diversified portfolio consisting primarily of equity securities, such as common stocks of issuers across the capitalization spectrum and identified by the Adviser as having value characteristics.

 

The Adviser examines various factors in determining the value characteristics of such issuers including price to book value ratios and price to earnings ratios. These value characteristics are examined in the context of the issuer's operating and financial fundamentals, such as return on equity and earnings growth and cash flow. The Adviser selects securities for the Fund based on a continuous study of trends in industries and companies, earnings power and growth and other investment criteria.

 

The Adviser will sell a stock when it no longer meets one or more investment criteria, either through obtaining target value or due to an adverse change in fundamentals or business momentum. Each holding has a target valuation established at purchase, which the Adviser constantly monitors and adjusts as appropriate.

 

The Fund may also invest up to 20% of its total assets in non U.S. dollar-denominated securities.

 

The Fund may invest up to 15% of its net assets in illiquid securities, including securities that are illiquid by virtue of the absence of a readily available market or legal or contractual restrictions on resale.

 

The Fund may participate as a purchaser in initial public offerings of securities ("IPO"). An IPO is a company's first offering of stock to the public.

 

The Fund may invest up to 10% of its net assets in securities that can be converted into common stock, such as certain debt securities and preferred stock.

 

The Fund may hedge overall portfolio exposure up to 40% of its net assets through the purchase and sale of index and individual put and call options.

 

In general, the Fund's investments are broadly diversified over a number of industries and, as a matter of policy, the Fund is limited to investing less than 25% of its total assets in any one industry.

 

While the Adviser intends to fully invest the Fund's assets at all times in accordance with the above-mentioned policies, the Fund reserves the right to hold up to 100% of its assets, as a temporary defensive measure, in cash and eligible U.S. dollar-denominated money market instruments and make investments inconsistent with its investment objective. The Adviser will determine when market conditions warrant temporary defensive measures.

Risk [Heading] rr_RiskHeading Summary of Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The 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 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.

 

Convertible Securities Risk. Securities that can be converted into common stock, such as certain securities and preferred stock, are subject to the usual risks associated with fixed income investments, such as interest rate risk and credit risk. In addition, because they react to changes in the value of the equity securities into which they will convert, convertible securities are also subject to the risks associated with equity securities.

 

Cyber Security Risk. Cyber security risk is the risk of an unauthorized breach and access to Fund assets, Fund or customer data (including private shareholder information), or proprietary information, or the risk of an incident occurring that causes the Fund, the investment adviser, custodian, transfer agent, distributor and other service providers and financial intermediaries to suffer data breaches, data corruption or lose operational functionality or prevent Fund investors from purchasing, redeeming or exchanging shares or receiving distributions. The Fund and its investment 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 Fund or its service providers may adversely impact and cause financial losses to the Fund or its shareholders.

 

Foreign Custody Risk. The Fund may hold foreign securities and cash with foreign banks, agents, and securities depositories appointed by the Fund's custodian (each a "Foreign Custodian"). Some Foreign Custodians may be recently organized or new to the foreign custody business. In some countries, Foreign Custodians may be subject to little or no regulatory oversight over or independent evaluation of their operations. Further, the laws of certain countries may place limitations on the Fund's ability to recover its assets if a Foreign Custodian enters bankruptcy. Investments in emerging markets may be subject to even greater custody risks than investments in more developed markets. Custody services in emerging market countries are very often undeveloped and may be considerably less well-regulated than in more developed countries, and thus may not afford the same level of investor protection as would apply in developed countries.

 

Foreign Securities Risk. International investing is subject to special risks, including, but not limited to, currency exchange rate volatility, political, social or economic instability, and differences in taxation, auditing and other financial practices.

 

Illiquid Securities Risk. Investing in illiquid securities is subject to certain risks, such as limitations on resale and uncertainty in determining valuation. Limitations on resale may adversely affect the marketability of portfolio securities and the Fund might be unable to dispose of restricted or other illiquid securities promptly or at reasonable prices and might thereby experience difficulty satisfying redemptions within seven days. The Fund might, in order to dispose of restricted securities, have to register securities resulting in additional expense and delay. Adverse market conditions could impede such a public offering of such securities.

 

IPO Risk. IPO risk is the risk that the market value of IPO shares will fluctuate considerably due to certain factors, such as the absence of a prior public market, unseasoned trading, the small number of shares available for trading and limited information about the issuer. The purchase of IPO shares may involve high transaction costs. IPO shares are subject to market risk and liquidity risk. When the Fund's asset base is small, a significant portion of the Fund's performance could be attributable to investments in IPOs, because such investments would have a magnified impact on the Fund. As the Fund's assets grow, the effect of the Fund's investments in IPOs on the Fund's performance probably will decline, which could reduce the Fund's performance. Because of the price volatility of IPO shares, the Fund may choose to hold IPO shares for a very short period of time. This may increase the turnover of the Fund's portfolio and may lead to increased expenses to the Fund, such as commissions and transaction costs. In addition, the Adviser cannot guarantee continued access to IPOs.

 

Management Risk. The Fund is subject to the risk of poor stock selection. In other words, the individual stocks in the Fund may not perform as well as expected, and/or the Fund's portfolio management practices do not work to achieve their desired result.

 

Market Risk. The net asset value ("NAV") of the Fund will change with changes in the market value of its portfolio positions. Investors may lose money. Although the Fund will invest in stocks the Adviser believes to be undervalued, there is no guarantee that the prices of these stocks will not move even lower.

 

Micro-Cap Companies Risk. Micro-cap stocks may be very sensitive to changing economic conditions and market downturns because the issuers often have narrow markets for their products or services, fewer product lines, and more limited managerial and financial resources than larger issuers. The stocks of micro-cap companies may therefore be more volatile and the ability to sell them at a desirable time or price may be more limited.

 

Mid-Cap Companies Risk. The stocks of mid-sized companies may be subject to more abrupt or erratic market movements than stocks of larger, more established companies.

 

Options Risk. An option is a type of derivative instrument that gives the holder the right (but not the obligation) to buy (a "call") or sell (a "put") an asset in the near future at an agreed upon price prior to the expiration date of the option. The Fund may "cover" a call option by owning the security underlying the option or through other means. The value of options can be highly volatile, and their use can result in loss if the Adviser is incorrect in its expectation of price fluctuations.

 

Small-Cap Companies Risk. The stocks of smaller companies may be subject to more abrupt, erratic market movements than stocks of larger, more established companies. Small companies may have limited product lines or financial resources, or may be dependent on a small or inexperienced management group, and their securities may trade less frequently and in lower volume than securities of larger companies, which could lead to higher transaction costs. Generally, the smaller the company size, the greater the risk.

Risk Lose Money [Text] rr_RiskLoseMoney You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the long-term performance of the Boston Partners All-Cap Value Fund's Institutional Class. The bar chart below shows you how the performance of the Fund's Institutional Class has varied year by year and provides some indication of the risks of investing in the Fund. The bar chart assumes reinvestment of dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. Performance reflects fee waivers in effect. If fee waivers were not in place, the Fund's performance would be reduced. Updated performance information is available at www.boston-partners.com or 1-888-261-4073.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart below shows you how the performance of the Fund's Institutional Class has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-888-261-4073
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.boston-partners.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture As with all such investments, past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Total Returns for the Calendar Years Ended December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best and Worst Quarterly Performance (for the periods reflected in the chart above):

 

Best Quarter: 18.60% (quarter ended June 30, 2009)
Worst Quarter: -17.49% (quarter ended September 30, 2011)

 

The year-to-date total return for the nine months ended September 30, 2019 was 17.07%.

Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns for the Periods Ended December 31, 2018
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In certain cases, the figure representing "Return after Taxes on Distributions and Sale of Fund Shares" may be higher than the other return figures for the same period, since a higher after-tax return results when a capital loss occurs upon redemption and provides an assumed tax deduction that benefits the investor.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The table below compares the average annual total returns for the Fund's Institutional Class both before and after taxes for the past calendar year, past five calendar years and past ten calendar years to the average annual total returns of a broad-based securities market index for the same periods.

Boston Partners Institutional | Boston Partners All-Cap Value Fund | INSTITUTIONAL  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol BPAIX
Management Fees rr_ManagementFeesOverAssets 0.70%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.12%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.83%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.03%) [2]
Total Annual Fund Operating Expenses after Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.80%
One Year rr_ExpenseExampleYear01 $ 817
Three Years rr_ExpenseExampleYear03 2,619
Five Years rr_ExpenseExampleYear05 4,575
Ten Years rr_ExpenseExampleYear10 $ 10,226
Annual Return 2009 rr_AnnualReturn2009 30.97%
Annual Return 2010 rr_AnnualReturn2010 13.42%
Annual Return 2011 rr_AnnualReturn2011 (1.38%)
Annual Return 2012 rr_AnnualReturn2012 15.83%
Annual Return 2013 rr_AnnualReturn2013 39.12%
Annual Return 2014 rr_AnnualReturn2014 12.23%
Annual Return 2015 rr_AnnualReturn2015 0.95%
Annual Return 2016 rr_AnnualReturn2016 14.82%
Annual Return 2017 rr_AnnualReturn2017 17.87%
Annual Return 2018 rr_AnnualReturn2018 (11.87%)
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2019
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 17.07%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.60%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.49%)
1 Year rr_AverageAnnualReturnYear01 (11.87%)
5 Years rr_AverageAnnualReturnYear05 6.21%
10 Years rr_AverageAnnualReturnYear10 12.30%
Boston Partners Institutional | Boston Partners All-Cap Value Fund | Russell 3000® Value Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (8.58%)
5 Years rr_AverageAnnualReturnYear05 5.77%
10 Years rr_AverageAnnualReturnYear10 11.12%
Boston Partners Institutional | Boston Partners All-Cap Value Fund | After Taxes on Distributions | INSTITUTIONAL  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (13.13%) [3]
5 Years rr_AverageAnnualReturnYear05 4.90% [3]
10 Years rr_AverageAnnualReturnYear10 11.26% [3]
Boston Partners Institutional | Boston Partners All-Cap Value Fund | After Taxes on Distributions and Sales | INSTITUTIONAL  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (6.05%)
5 Years rr_AverageAnnualReturnYear05 4.77%
10 Years rr_AverageAnnualReturnYear10 10.16%
[1] Acquired fund fees and expenses are indirect fees and expenses that the Fund incurs from investing in the shares of other mutual funds, including money market funds and exchange-traded funds. Please note that the amount of Total annual Fund operating expenses and Total annual Fund operating expenses after fee waiver and/or expense reimbursement shown in the above table will differ from the "Financial Highlights" section of the prospectus, which reflects the operating expenses of the Fund and does not include indirect expenses such as acquired fund fees and expenses.
[2] The Fund's investment adviser, Boston Partners Global Investors, Inc. (the "Adviser"), has contractually agreed to waive all or a portion of its advisory fee and/or reimburse expenses in an aggregate amount equal to the amount by which the Total annual Fund operating expenses (excluding certain items discussed below) for the Fund's Institutional Class shares exceeds 0.80% of the average daily net assets attributable to the Fund's Institutional Class shares. In determining the Adviser's obligation to waive advisory fees and/or reimburse expenses, the following expenses are not taken into account and could cause net Total annual Fund operating expenses to exceed 0.80%: short sale dividend expenses, brokerage commissions, extraordinary items, interest or taxes. This contractual limitation is in effect until February 28, 2021 and may not be terminated without the approval of the Board of Directors of The RBB Fund, Inc. If at any time the Fund's Total annual fund operating expenses (not including short sale dividend expense, brokerage commissions, extraordinary items, interest or taxes) for a year are less than 0.80% or the expense cap then in effect, whichever is less, the Adviser is entitled to reimbursement by the Fund of the advisory fees forgone and other payments remitted by the Adviser to the Fund within three years from the date on which such waiver or reimbursement was made, provided such reimbursement does not cause the Fund to exceed expense limitations that were in effect at the time of the waiver or reimbursement.
[3] After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. In certain cases, the figure representing "Return after Taxes on Distributions and Sale of Fund Shares" may be higher than the other return figures for the same period, since a higher after-tax return results when a capital loss occurs upon redemption and provides an assumed tax deduction that benefits the investor.