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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Ariel International Equity Fund
Objective [Heading] rr_ObjectiveHeading Investment objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
Ariel International Equity Fund pursues long-term capital appreciation.
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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-09-30
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 period, the Fund’s portfolio turnover rate was 21% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 21.00%
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below illustrates the expenses you would pay on a $10,000 investment in Ariel International Equity 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 reflects contractual fee waivers and expense reimbursements through September 30, 2015.  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 International Equity Fund invests primarily in common stock issued by companies outside the U.S. in developed international markets.  The Fund may invest in large, medium, or small companies without regard to market capitalization.  Under normal market conditions, the Fund will invest at least 80% of its assets (net assets plus any borrowings for investment purposes) in equity securities.  The Fund may buy and sell currency on a spot basis and enter into foreign currency forward contracts for portfolio management.

The Fund may buy or sell foreign currency options and securities, securities index options, futures contracts and related options, and enter into swap agreements, which are types of derivatives.  These techniques may be used for any legally permissible purpose, including seeking to increase the Fund’s return through the use of derivatives as a substitute for securities or to reduce the risk of loss of certain holdings.  The Fund may also invest in exchange traded funds (“ETFs”).

The Fund’s investment process seeks to identify investment opportunities offering superior risk-adjusted returns by pursuing a “bottom-up” stock picking discipline that focuses on both the fundamentals of the business and the intrinsic value of the business.  Particular attention is paid to normalized cash flow generation and reinvestment or distribution for shareholder benefit.

We will consider selling a stock if its valuation reaches our investment goals, if a better opportunity for investment presents itself, or if there are material adverse changes to a company’s fundamentals.

Ariel International Equity Fund is a diversified fund that will generally hold between 40-150 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
The general level of stock prices could decline.

v
Investments in foreign securities may underperform and may be more volatile than comparable U.S. stocks.  Foreign economies and markets may not be as strong or well regulated, foreign political systems may not be as stable, and foreign financial reporting and disclosure standards may not be as rigorous as those in the U.S.

v
Securities issued by foreign companies are typically denominated in foreign currencies, resulting in a risk that adverse exchange rate fluctuations against the U.S. dollar could create losses and could depress prices for extended periods of time.  The use of foreign currency derivatives may be expensive and may result in further losses.

v
The use of various types of derivatives may intensify investment losses from securities underlying the derivatives, may create more volatility and may expose the Fund to other losses and expenses. Certain derivatives, such as swap transactions, may entail the risk that a counterparty or party will default on payment or other obligations under the derivative.

v
ETFs may be less liquid and subsequently more volatile than the underlying portfolio of securities.  ETFs also have management fees that increase the cost compared to owning the underlying securities directly.

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.

 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 MSCI EAFE® Index, a broad measure of market performance.  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 : 4Q '12 +6.79%
Worst Quarter : 2Q '12 -11.41%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 6.79%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2012
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (11.41%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deductions for fees, expenses or taxes)
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns
MSCI EAFE® Index (reflects no deductions for fees, expenses or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 17.90%
Since Inception rr_AverageAnnualReturnSinceInception 17.85%
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 1.00%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 15.75%
Total annual operating expenses rr_ExpensesOverAssets 17.00% [1]
Less fee waiver or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (15.60%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 143
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 443
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 3,784
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 9,199
Annual Return 2012 rr_AnnualReturn2012 4.34%
1 Year rr_AverageAnnualReturnYear01 4.34%
Since Inception rr_AverageAnnualReturnSinceInception 4.32%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2011
Investor Class | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.34%
Since Inception rr_AverageAnnualReturnSinceInception 4.32%
Investor Class | After Taxes on Distributions and Sales
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.21%
Since Inception rr_AverageAnnualReturnSinceInception 3.84%
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 1.00%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 14.70%
Total annual operating expenses rr_ExpensesOverAssets 15.70% [1]
Less fee waiver or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (14.55%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.15%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 117
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 365
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 3,516
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 8,876
1 Year rr_AverageAnnualReturnYear01 4.60%
Since Inception rr_AverageAnnualReturnSinceInception 4.58%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2011
[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel International Equity Fund's total annual operating expenses to 1.40% of net assets for the Investor Class and 1.15% of net assets for Class I through the end of the fiscal year ending September 30, 2015. No termination of this agreement by either the Board of Trustees or the Adviser may be effective until, at the earliest, October 1, 2015.