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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Ariel Fund
Objective [Heading] rr_ObjectiveHeading Investment objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
Ariel Fund pursues long-term capital appreciation by investing in undervalued companies that show strong potential for growth.
Expense [Heading] rr_ExpenseHeading Fees and expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The table below describes fees and expenses that you may pay if you buy and hold 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).  Higher turnover rates may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account.  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 27% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 27.00%
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Fund.  It assumes the Fund earned an annual return of 5% each year, the Fund’s operating expenses remain the same and that you redeem your shares at the end of each time period. The example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.  Your actual expenses may be greater or less than the amounts shown.
Strategy [Heading] rr_StrategyHeading Principal investment strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Ariel Fund invests primarily in common stocks of U.S. companies and the Fund generally will have a weighted average market capitalization between $1 billion and $7.5 billion.  The Fund will not hold stocks that fall within the top two quintiles of the Russell U.S. equity indexes (a comprehensive representation of market-cap weighted security indexes of the investable U.S. equity market) and if such stock falls within the top two quintiles, it will be sold by the end of the following quarter.

The essence of the Fund’s strategy is a combination of patience and stock selection.  The Fund seeks to hold investments for a relatively long period of time—generally five years.

The Fund seeks to invest in quality companies in industries in which Ariel Investments, LLC (“Ariel” or the “Adviser”) has expertise including the financial services and consumer discretionary sectors.  The Fund only buys when Ariel believes that these businesses are selling at excellent values.

Quality companies typically share several attributes that Ariel believes will result in capital appreciation over time: high barriers to entry, sustainable competitive advantages, predictable fundamentals that allow for double-digit earnings growth, skilled management teams and solid financials.  Ariel’s strategy to focus on a limited number of names and industries is designed to add value in areas in which it has expertise.  We believe this approach creates a portfolio of well-researched stocks.  As disciplined value investors, we make opportunistic purchases when great companies are temporarily out of favor—generally seeking to invest in companies that are trading at a low valuation relative to potential earnings and/or a low valuation relative to intrinsic worth.  We will sell a stock if its valuation reaches our private market value, as determined by the Adviser, if a better opportunity for investment presents itself, or if there are material changes to a company’s fundamentals.

The Fund does not invest in corporations whose primary source of revenue is derived from the production or sale of tobacco products or the manufacture of handguns.  We believe these industries are more likely to face shrinking growth prospects, draining litigation costs and legal liability that cannot be quantified.

Ariel Fund is a diversified fund that will generally hold between 30–50 securities in its portfolio.
Risk [Heading] rr_RiskHeading Principal risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
Although Ariel makes every effort to achieve the Fund’s objective of long-term capital appreciation, Ariel cannot guarantee it will attain that objective.  You could lose money by investing in this Fund.  The principal risks are:

v
Small and medium capitalization stocks held by the Fund could fall out of favor and returns would subsequently trail returns from the overall stock market.  The performance of such stocks could also be more volatile.

v
The general level of stock prices could decline.

v
The Fund often invests a significant portion of its assets in companies within the financial services and consumer discretionary sectors and its performance may suffer if these sectors underperform the overall stock market.

You should consider investing in the Fund if you are looking for long-term capital appreciation and are willing to accept the associated risks.
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in this Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The bar chart and the table below show two aspects of the Fund: variability and performance.  The bar chart shows the variability of the Fund’s Investor Class annual total returns over time by showing changes in the Fund’s Investor Class performance from year to year.  The table shows the Fund’s average annual total returns for certain time periods compared to the returns of the S&P 500 Index, a broad measure of market performance, and indices that reflect the market sectors in which the Fund invests.  The bar chart and table provide some indication of the risks of investing in the Fund.  To obtain updated performance information, visit the Fund’s website at arielinvestments.com or call 800.292.7435.  The Fund’s past performance, before and after taxes, is not necessarily an indication of its future performance.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and the table below show two aspects of the Fund: variability and performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800.292.7435
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress arielinvestments.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance, before and after taxes, is not necessarily an indication of its future performance.
Bar Chart [Heading] rr_BarChartHeading Total Return for the Year Ended December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter : 2Q '09 +34.75%
Worst Quarter : 4Q '08 -34.28%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 34.75%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (34.28%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deductions for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After tax returns are calculated using the highest historical 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 your tax situation and are not relevant if Fund shares are held in tax-deferred arrangements, such as Individual Retirement Accounts (IRAs).
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes.  Actual after-tax returns depend on your tax situation and are not relevant if Fund shares are held in tax-deferred arrangements, such as Individual Retirement Accounts (IRAs).
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns
S&P 500® Index (reflects no deductions for fees, expenses or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 16.00%
5 Years rr_AverageAnnualReturnYear05 1.66%
10 Years rr_AverageAnnualReturnYear10 7.10%
Since Inception rr_AverageAnnualReturnSinceInception 9.46%
Russell 2500 Value Index (reflects no deductions for fees, expenses or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 19.21%
5 Years rr_AverageAnnualReturnYear05 4.54%
10 Years rr_AverageAnnualReturnYear10 10.20%
Since Inception rr_AverageAnnualReturnSinceInception 11.03%
Russell 2000 Value Index (reflects no deductions for fees, expenses or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 18.05%
5 Years rr_AverageAnnualReturnYear05 3.55%
10 Years rr_AverageAnnualReturnYear10 9.50%
Since Inception rr_AverageAnnualReturnSinceInception 10.33%
Investor Class
  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Maximum sales charge (load) imposed on reinvested dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual operating expenses rr_ExpensesOverAssets 1.06%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 108
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 337
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 585
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,294
Annual Return 2003 rr_AnnualReturn2003 28.04%
Annual Return 2004 rr_AnnualReturn2004 21.97%
Annual Return 2005 rr_AnnualReturn2005 0.92%
Annual Return 2006 rr_AnnualReturn2006 10.35%
Annual Return 2007 rr_AnnualReturn2007 (1.70%)
Annual Return 2008 rr_AnnualReturn2008 (48.25%)
Annual Return 2009 rr_AnnualReturn2009 63.42%
Annual Return 2010 rr_AnnualReturn2010 25.97%
Annual Return 2011 rr_AnnualReturn2011 (11.34%)
Annual Return 2012 rr_AnnualReturn2012 20.32%
1 Year rr_AverageAnnualReturnYear01 20.32%
5 Years rr_AverageAnnualReturnYear05 2.59%
10 Years rr_AverageAnnualReturnYear10 6.87%
Since Inception rr_AverageAnnualReturnSinceInception 10.75%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 06, 1986
Investor Class | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 20.15%
5 Years rr_AverageAnnualReturnYear05 2.50%
10 Years rr_AverageAnnualReturnYear10 6.41%
Since Inception rr_AverageAnnualReturnSinceInception 9.30%
Investor Class | After Taxes on Distributions and Sales
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 13.43%
5 Years rr_AverageAnnualReturnYear05 2.19%
10 Years rr_AverageAnnualReturnYear10 5.99%
Since Inception rr_AverageAnnualReturnSinceInception 9.03%
Institutional Class (Class I)
  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Maximum sales charge (load) imposed on reinvested dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.08%
Total annual operating expenses rr_ExpensesOverAssets 0.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 69
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 379
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 847
1 Year rr_AverageAnnualReturnYear01 20.75% [1]
5 Years rr_AverageAnnualReturnYear05 2.66% [1]
10 Years rr_AverageAnnualReturnYear10 6.90% [1]
Since Inception rr_AverageAnnualReturnSinceInception 10.76% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 06, 1986 [1]
[1] The inception date for the Institutional Class shares is December 30, 2011. Performance information for the Institutional Class prior to that date reflects the actual performance of the Fund's Investor Class (and uses the actual expenses of the Investor Class, for such period of time), without any adjustments.