Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 31, 2012
ROBECO WPG SMALL/MICRO CAP VALUE FUND (Prospectus Summary) | ROBECO WPG SMALL/MICRO CAP VALUE FUND
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY SECTION
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks capital appreciation by investing primarily in common stocks, securities convertible into common stocks and in special situations.
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 and hold Institutional Class shares of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
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 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, 2012, the portfolio turnover rate for the Fund was 84%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	84.00%
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 $10,000 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	Currently, the Fund pursues its objective by investing, under normal circumstances, at least 80% of its net assets (including borrowings for investment purposes) in equity securities of U.S. companies, that, at the time of purchase, have a market capitalization that is within the range of the market capitalization of issuers in the Russell 2000® Value Index. As of November 30, 2012, the median market capitalization of the companies in the Russell 2000® Value Index is $433 million and the largest stock is $4.8 billion. The Fund may invest indepository receipts and equity securities of foreign companies. Although the Fund invests primarily in common stocks, the Fund may invest in all types of equity and equity-related securities, including (without limitation): o Securities convertible into common stocks. o Shares of real estate investment trusts ("REITs"). o Warrants and rights to purchase common stocks. o Preferred stocks. o Exchange traded limited partnerships. Special Situations: The Fund may invest in companies that may experience unusual and possibly unique developments which may create a special opportunity for significant returns. Special situations include: significant technological improvements or important discoveries; reorganizations, recapitalizations or mergers; favorable resolutions of litigation; new management or material changes in company policies; and actual or potential changes in control of a company. Strategies: Robeco uses a value approach to select the Fund's investments. Using this investment style, Robeco seeks securities selling at substantial discounts to their underlying values and then holds these securities until the market values reflect what Robeco believes to be their intrinsic values. Robeco employs a bottom-up strategy, focusing on undervalued industries that Robeco believes are experiencing positive change. Robeco then uses both qualitative and quantitative methods to assess a security's potential value. The portfolio managers managing the Fund meet with a multitude of companies annually to identify companies with increasing returns on capital in their core businesses which are selling at attractive valuations. Factors Robeco looks for in selecting investments include (without limitation): o Increasing returns on invested capital. o Companies who have demonstrated an ability to generate high return on invested capital (ROIC). o Companies which provide solid cash flows with appropriate capital. o Potential catalysts such as new products, cyclical upturns and changes in management. o Low market valuations relative to earnings forecast, book value, cash flow and sales. Robeco 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 Robeco constantly monitors and adjusts as appropriate.
Risk [Heading]	rr_RiskHeading	Summary of Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	o 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 Robeco believes to be undervalued, there is no guarantee that the price of these stocks will not move even lower. o 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. o 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. o Small Cap Companies Risk. The small capitalization equity securities in which the Fund may invest will often be traded only in the over-the-counter market or on a regional securities exchange, may be listed only in the quotation service commonly known as the "pink sheets," and may not be traded every day or in the volume typical of trading on a national securities exchange. These securities may also be subject to wide fluctuations in market value. The trading market for any given small capitalization equity security may be sufficiently small as to make it difficult for the Fund to dispose of a substantial block of such securities. The sale by the Fund of portfolio securities to meet redemptions may require the Fund to sell its small capitalization securities at a discount from market prices or during periods when, in Robeco's judgment, such sale is not desirable. Moreover, the lack of an efficient market for these securities may make them difficult to value. o 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. o REITs Risk. REITs may be affected by economic forces and other factors related to the real estate industry. Investing in REITs may involve risks similar to those associated with investing in small capitalization companies. REITs may have limited financial resources, may trade less frequently and in a limited volume and may be subject to more abrupt or erratic price movements than larger company securities. Historically, small capitalization stocks, such as REITs, have been more volatile in price than the larger capitalization stocks included in the S&P 500® Index. o Special Situations Risk. The Fund will seek to benefit from "special situations," such as mergers, reorganizations, or other unusual events expected to affect a particular issuer. There is a risk that the "special situation" might not occur or involve longer time frames than originally expected, which could have a negative impact on the price of the issuer's securities and fail to produce gains or produce a loss for the Fund. o Rights and Warrants Risk. The purchase of rights or warrants involves the risk that the Fund could lose the purchase value of a right or warrant if the right to subscribe to additional shares is not executed prior to the right's or warrant's expiration. Also, the purchase of rights and/or warrants involves the risk that the effective price paid for the right and/or warrant added to the subscription price of the related security may exceed the value of the subscribed security's market price such as when there is no movement in the level of the underlying security.
Risk Lose Money [Text]	rr_RiskLoseMoney	The net asset value ("NAV") of the Fund will change with changes in the market value of its portfolio positions. Investors may lose money.
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 Robeco WPG Small/Micro Cap Value Fund's Institutional Class. The performance for periods prior to April 29, 2005 represents the performance of the WPG Tudor Fund (the "Predecessor Fund"). The Predecessor Fund began operations on September 11, 1985. On April 29, 2005, the Predecessor Fund was reorganized as a new portfolio of the Company. Prior to the reorganization, the Predecessor Fund offered only one class of shares. In connection with the reorganization, shareholders of the Predecessor Fund exchanged their shares for Institutional Class shares of the Fund. The bar chart below shows you how the performance of the Fund's Institutional Class has varied year to 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.robecoinvest.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 to 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.robecoinvest.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: 28.51% (quarter ended June 30, 2009) Worst Quarter: (30.21)% (quarter ended December 31, 2008) Year-to-date total return for the nine months ended September 30, 2012: 17.35%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	reflects no deduction for fees, expenses or taxes
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 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 10 calendar years to the average annual total returns of a broad-based securities market index for the same periods.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)	[1]
ROBECO WPG SMALL/MICRO CAP VALUE FUND (Prospectus Summary) | ROBECO WPG SMALL/MICRO CAP VALUE FUND | Russell 2000® Value Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 2000® Value Index (reflects no deduction for fees, expenses or taxes)
1 Year	rr_AverageAnnualReturnYear01	(5.50%)
5 Years	rr_AverageAnnualReturnYear05	(1.88%)
10 Years	rr_AverageAnnualReturnYear10	6.40%
ROBECO WPG SMALL/MICRO CAP VALUE FUND (Prospectus Summary) | ROBECO WPG SMALL/MICRO CAP VALUE FUND | INSTITUTIONAL CLASS
Risk Return [Abstract]	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption fee (as a percentage of amount redeemed on shares held for less than 60 days, if applicable)	rr_RedemptionFeeOverRedemption	(2.00%)
Exchange fee (as a percentage of amount exchanged on shares held for less than 60 days, if applicable)	rr_ExchangeFeeOverRedemption	2.00%
Management Fees	rr_ManagementFeesOverAssets	0.90%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.80%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.70%
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Net expenses	rr_NetExpensesOverAssets	1.70%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	173
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	535
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	922
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,007
Annual Return 2002	rr_AnnualReturn2002	(26.10%)
Annual Return 2003	rr_AnnualReturn2003	45.37%
Annual Return 2004	rr_AnnualReturn2004	19.35%
Annual Return 2005	rr_AnnualReturn2005	(2.00%)
Annual Return 2006	rr_AnnualReturn2006	23.38%
Annual Return 2007	rr_AnnualReturn2007	(7.04%)
Annual Return 2008	rr_AnnualReturn2008	(38.73%)
Annual Return 2009	rr_AnnualReturn2009	41.23%
Annual Return 2010	rr_AnnualReturn2010	26.10%
Annual Return 2011	rr_AnnualReturn2011	(11.95%)
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-date total return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	17.35%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	28.51%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(30.21%)
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(11.95%)
5 Years	rr_AverageAnnualReturnYear05	(2.23%)
10 Years	rr_AverageAnnualReturnYear10	3.31%
ROBECO WPG SMALL/MICRO CAP VALUE FUND (Prospectus Summary) | ROBECO WPG SMALL/MICRO CAP VALUE FUND | INSTITUTIONAL CLASS | After Taxes on Distributions
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions	[3]
1 Year	rr_AverageAnnualReturnYear01	(11.95%)
5 Years	rr_AverageAnnualReturnYear05	(3.09%)
10 Years	rr_AverageAnnualReturnYear10	1.97%
ROBECO WPG SMALL/MICRO CAP VALUE FUND (Prospectus Summary) | ROBECO WPG SMALL/MICRO CAP VALUE FUND | INSTITUTIONAL CLASS | After Taxes on Distributions and Sales
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Shares
1 Year	rr_AverageAnnualReturnYear01	(7.76%)
5 Years	rr_AverageAnnualReturnYear05	(2.23%)
10 Years	rr_AverageAnnualReturnYear10	2.26%

[1] The performance record prior to August 18, 2003 was achieved under the Predecessor Fund's growth-related strategy.

[2] The Fund's investment adviser, Robeco Investment Management, Inc. ("Robeco") has contractually agreed to waive 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 exceeds 1.70% of the average daily net assets attributable to the Fund's Institutional Class shares. In determining Robeco'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 1.70%: acquired fund fees and expenses, short sale dividend expenses, brokerage commissions, extraordinary items, interest or taxes. This contractual limitation is in effect until December 31, 2013 and may not be terminated without the approval of the Board of Directors of The RBB Fund, Inc. Robeco may not recoup any of its waived investment advisory fee. The amount waived for the fiscal year ended August 31, 2012 was less than 0.01%.

[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. The table, like the bar chart, provides some indication of the risks of investing in the Fund by showing how the Fund's average annual total returns for the one year, five year, and since inception periods compare with those of a broad measure of market performance.