Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 31, 2012
ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II (Second Prospectus Summary) | ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II
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 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 and hold Investor 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 most recent fiscal year end, the portfolio turnover rate for the Fund was 32%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	32.00%
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	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 with small market capitalizations and identified by Robeco as having value characteristics. A small market capitalization issuer generally is considered to be one whose market capitalization is, at the time the Fund makes the investment, similar to the market capitalization of companies in the Russell 2000® Value Index. The Russell 2000® Value Index is an unmanaged index that contains stocks from the Russell 2000® Index with less than average growth orientation. As of November 30, 2012, the median market capitalization of this index was $490 million and the largest stock was $4.8 billion. Please note that this range is as of a particular point in time and is subject to change. The Fund generally invests in the equity securities of small companies. Robeco will seek to invest in companies it considers to be well managed and to have attractive fundamental financial characteristics. Robeco believes greater potential for price appreciation exists among small companies since they tend to be less widely followed by other securities analysts and thus may be more likely to be undervalued by the market. The Fund may invest from time to time a portion of its assets, not to exceed 20% (under normal conditions) at the time of purchase, in companies with larger market capitalizations. 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. Robeco 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, earnings growth and cash flow. Robeco 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 Fund may also invest up to 25% 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. 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 a maximum of 25% of its total assets in any one industry. While Robeco 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. Robeco will determine when market conditions warrant temporary defensive measures.
Risk [Heading]	rr_RiskHeading	Summary of Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	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 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 prices 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 Small Cap Companies Risk. The Fund will invest in smaller issuers which are more volatile and less liquid than investments in issuers with a market capitalization greater than the market capitalization of companies in the Russell 2000® Value Index. Small market capitalization issuers are not as diversified in their business activities as issuers with market capitalizations greater than the market capitalization of companies in the Russell 2000® Value Index and are more susceptible to changes in the business cycle. The small capitalization equity securities in which the Fund invests may 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 Portfolio Turnover Risk. If the Fund frequently trades its portfolio securities, the Fund will incur higher brokerage commissions and transaction costs, which could lower the Fund's performance. In addition to lower performance, high portfolio turnover could result in taxable capital gains. The annual portfolio turnover rate for the Fund is not expected to exceed 175%; however, it may be higher if Robeco believes it will improve the Fund's performance. o 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. o 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, Robeco cannot guarantee continued access to IPOs.
Risk Lose Money [Text]	rr_RiskLoseMoney	Investors may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The chart below illustrates the long-term performance of the Robeco Boston Partners Small Cap Value Fund II's Investor Class. The information shows you how the Fund's performance has varied year by year and provides some indication of the risks of investing in the Fund. The 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 information shows you how the Fund's performance 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.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:       29.32% (quarter ended June 30, 2009)              Worst Quarter:      (26.42)% (quarter ended December 31, 2008) Year-to-date total return for the nine months ended September 30, 2012: 18.57%
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	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.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The table below compares the average annual total returns for the Fund's Investor 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.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns for the Periods Ended December 31, 2011
ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II (Second Prospectus Summary) | ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II | 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 BOSTON PARTNERS SMALL CAP VALUE FUND II (Second Prospectus Summary) | ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II | INVESTOR 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	(1.00%)
Exchange fee (as a percentage of amount exchanged on shares held for less than 60 days, if applicable)	rr_ExchangeFeeOverRedemption	1.00%
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and servicing (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.36%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.61%
Less Fee waivers and expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.06%)	[1]
Net expenses	rr_NetExpensesOverAssets	1.55%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	158
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	503
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	871
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,908
Annual Return 2002	rr_AnnualReturn2002	(15.94%)
Annual Return 2003	rr_AnnualReturn2003	52.90%
Annual Return 2004	rr_AnnualReturn2004	16.47%
Annual Return 2005	rr_AnnualReturn2005	7.54%
Annual Return 2006	rr_AnnualReturn2006	15.66%
Annual Return 2007	rr_AnnualReturn2007	(7.56%)
Annual Return 2008	rr_AnnualReturn2008	(34.82%)
Annual Return 2009	rr_AnnualReturn2009	48.99%
Annual Return 2010	rr_AnnualReturn2010	18.24%
Annual Return 2011	rr_AnnualReturn2011	(3.67%)
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	18.57%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	29.32%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(26.42%)
Label	rr_AverageAnnualReturnLabel	Returns Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.67%)
5 Years	rr_AverageAnnualReturnYear05	0.45%
10 Years	rr_AverageAnnualReturnYear10	6.65%
ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II (Second Prospectus Summary) | ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II | INVESTOR CLASS | After Taxes on Distributions
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Returns After Taxes on Distributions	[2]
1 Year	rr_AverageAnnualReturnYear01	(3.72%)
5 Years	rr_AverageAnnualReturnYear05	(1.01%)
10 Years	rr_AverageAnnualReturnYear10	5.09%
ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II (Second Prospectus Summary) | ROBECO BOSTON PARTNERS SMALL CAP VALUE FUND II | INVESTOR CLASS | After Taxes on Distributions and Sales
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Returns After Taxes on Distributions and Sale of Fund Shares
1 Year	rr_AverageAnnualReturnYear01	(2.39%)
5 Years	rr_AverageAnnualReturnYear05	0.10%
10 Years	rr_AverageAnnualReturnYear10	5.51%

[1] The Fund's investment adviser, Robeco Investment Management, Inc. ("Robeco"), 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 Investor Class shares exceeds 1.55% of the average daily net assets attributable to the Fund's Investor 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 1.55%: 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 fees.

[2] 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.