485BPOS

Filed with the Securities and Exchange Commission on February 8, 2013

1933 Act Registration File No. 33-7699

1940 Act File No. 811-4786

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

[Missing Graphic Reference]

FORM N-1A

REGISTRATION STATEMENT UNDER THE

SECURITIES ACT OF 1933, AS AMENDED

REGISTRATION NO. 33-7699

Post-Effective Amendment No. 52

and

REGISTRATION STATEMENT UNDER THE

INVESTMENT COMPANY ACT OF 1940, AS AMENDED

REGISTRATION NO. 811-4786

Amendment No. 52

ARIEL INVESTMENT TRUST

(Exact Name of Registrant as Specified in Charter)

200 East Randolph Street, Suite 2900

Chicago, Illinois 60601

(Address of Principal Executive Offices)  (Zip Code)

Registrant’s Telephone Number, including Area Code:   (312) 726-0140

Agent for service:	With copies to:
Arthur Don, Esq. Greenberg Traurig, LLP 77 West Wacker Drive Chicago, Illinois 60601 312.456.8438	Anita Zagrodnik Ariel Investment Trust 200 East Randolph Street Suite 2900 Chicago, Illinois 60601 312.726.0140	Alia S. Vasquez, Esq. U.S. Bancorp Fund Services, LLC 777 East Wisconsin Avenue MailCode: MK-WI-T10F Milwaukee, Wisconsin 53202 414.765.6620

It is proposed that this filing will become effective:

ximmediately upon filing pursuant to paragraph (b)

oon (date) pursuant to paragraph (b)

o60 days after filing pursuant to paragraph (a)(1)

oon (date) pursuant to paragraph (a)(1)

o75 days after filing pursuant to paragraph (a)(2)

oon (date) pursuant to paragraph (a)(2) of rule 485.

Explanatory Note:  This Post-Effective Amendment (“PEA”) No. 52 to the Registration Statement of Ariel Investment Trust (the “Trust”) hereby incorporates Parts A, B and C from the Trust’s PEA No. 50 on Form N-1A filed on January 28, 2013.  This PEA No. 52 is filed for the sole purpose of submitting the XBRL exhibit for the risk/return summary first provided in PEA No. 50 to the Trust’s Registration Statement.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this registration statement under Rule 485(b) and has duly caused this Post-Effective Amendment No. 52 to its Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of Chicago and State of Illinois on the 8th day of February, 2013.

ARIEL INVESTMENT TRUST
By:	/s/ Mellody Hobson*
	Mellody Hobson,
	President

Pursuant to the requirements of the Securities Act of 1933, as amended, this Post-Effective Amendment No. 52 to the Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/ James W. Compton*	Trustee	February 8, 2013
James W. Compton
/s/ William C. Dietrich*	Trustee	February 8, 2013
William C. Dietrich
/s/ Royce N. Flippin, Jr.*	Lead Independent Trustee	February 8, 2013
Royce N. Flippin, Jr.
/s/ Christopher G. Kennedy*	Trustee	February 8, 2013
Christopher G. Kennedy
/s/ H. Carl McCall*	Trustee	February 8, 2013
H. Carl McCall
/s/ Mellody Hobson*	Principal Executive Officer, President	February 8, 2013
Mellody Hobson	and Trustee
/s/ Merrillyn J. Kosier*	Trustee	February 8, 2013
Merrillyn J. Kosier
/s/ John W. Rogers, Jr.*	Trustee	February 8, 2013
John W. Rogers, Jr.
/s/ James M. Williams*	Trustee	February 8, 2013
James M. Williams
/s/ William M. Lewis, Jr.*	Trustee	February 8, 2013
William M. Lewis, Jr.
/s/ Anita Zagrodnik	Principal Financial Officer,	February 8, 2013
Anita Zagrodnik	Principal Accounting Officer and Treasurer

*By:	/s/ Mellody Hobson
	Mellody Hobson,
	Attorney-in-fact

*Mellody Hobson signs this document on behalf of each of the foregoing persons pursuant to the Powers of Attorney.

 EXHIBIT INDEX

Exhibit	Exhibit No.
Instance Document	EX-101.INS
Schema Document	EX-101.SCH
Calculation Linkbase Document	EX-101.CAL
Definition Linkbase Document	EX-101.DEF
Label Linkbase Document	EX-101.LAB
Presentation Linkbase Document	EX-101.PRE

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Ariel Global Equity Fund | Ariel Global Equity Fund

Ariel Global Equity Fund

Investment objective

Ariel Global Equity Fund pursues long-term capital appreciation.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel Global Equity Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Maximum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel Global Equity Fund		Investor Class	Institutional Class (Class I)
Management fees		1.00%	1.00%
Distribution and service (12b-1) fees		0.25%	none
Other expenses		11.08%	3.07%
Total annual operating expenses	[1]	12.33%	4.07%
Less fee waiver or expense reimbursement		(10.93%)	(2.92%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.40%	1.15%

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Global 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.

Expense Example Ariel Global Equity Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	143	443	2,988	7,886
Institutional Class (Class I)	117	365	1,286	3,662

Portfolio turnover

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 26% of the average value of its portfolio.

Principal investment strategy

Ariel Global Equity Fund invests primarily in common stock issued by companies both within and outside the U.S., including in countries with developed or emerging 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 and at least 40% of its assets in countries other than the U.S.  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 Global Equity Fund is a diversified fund that will generally hold between 40-150 securities in its portfolio.

Principal risks

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 Investments in companies based in emerging or developing countries present risks greater than those in mature markets, including greater risk of adverse government intervention or economic turmoil, high inflation and more volatile interest and currency exchange rates.

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.

\Performance

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 ACWISM, 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.

Total Return for the Year Ended December 31

Best Quarter :	4Q '12	+5.29%
Worst Quarter :	2Q '12	-8.94%

Average Annual Total Returns

Average Annual Returns Ariel Global Equity Fund	1 Year	Since Inception	Inception Date
Investor Class	5.50%	5.48%	Dec. 30, 2011
Institutional Class (Class I)	5.79%	5.77%	Dec. 30, 2011
After Taxes on Distributions Investor Class	5.50%	5.48%
After Taxes on Distributions and Sales Investor Class	3.58%	4.66%
MSCI ACWISM (reflects no deductions for fees, expenses or taxes)	16.80%	16.75%

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Global 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.

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Ariel Appreciation Fund | Ariel Appreciation Fund

Ariel Appreciation Fund

Investment objective

Ariel Appreciation Fund pursues long-term capital appreciation by investing in undervalued companies that show strong potential for growth.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel Appreciation Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Maximum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel Appreciation Fund	Investor Class	Institutional Class (Class I)
Management fees	0.71%	0.71%
Distribution and service (12b-1) fees	0.25%	none
Other expenses	0.21%	0.28%
Total annual operating expenses	1.17%	0.99%

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Appreciation 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.

Expense Example Ariel Appreciation Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	119	372	644	1,420
Institutional Class (Class I)	101	315	547	1,213

Portfolio turnover

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 28% of the average value of its portfolio.

Principal investment strategy

Ariel Appreciation Fund invests primarily in common stocks of U.S. companies and the Fund generally will have a weighted average market capitalization between $2 billion and $15 billion.  The Fund will not hold stocks that fall within the top quintile 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 quintile, 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 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 Appreciation Fund is a diversified fund that will generally hold between 30–50 securities in its portfolio.

Principal risks

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 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.

Performance

The bar chart and the table 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.

Total Return for the Year Ended December 31

Best Quarter :	2Q '09	+29.74%
Worst Quarter :	4Q '08	-29.88%

Average Annual Total Returns

Average Annual Returns Ariel Appreciation Fund		1 Year	5 Years	10 Years	Since Inception	Inception Date
Investor Class		19.35%	5.02%	7.86%	10.24%	Dec. 01, 1989
Institutional Class (Class I)	[1]	19.62%	5.06%	7.88%	10.25%	Dec. 01, 1989
After Taxes on Distributions Investor Class		17.33%	4.14%	7.02%	9.03%
After Taxes on Distributions and Sales Investor Class		15.00%	4.03%	6.73%	8.76%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		16.00%	1.66%	7.10%	8.57%
Russell Midcap Value Index (reflects no deductions for fees, expenses or taxes)		18.51%	3.79%	10.63%	11.02%
Russell Midcap Index (reflects no deductions for fees, expenses or taxes)		17.28%	3.57%	10.65%	10.72%

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).

[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.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Ariel Global Equity Fund

Objective [Heading]

rr_ObjectiveHeading

Investment objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Ariel Global 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 26% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

26.00%

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Global 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 Global Equity Fund invests primarily in common stock issued by companies both within and outside the U.S., including in countries with developed or emerging 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 and at least 40% of its assets in countries other than the U.S.  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 Global 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 Investments in companies based in emerging or developing countries present risks greater than those in mature markets, including greater risk of adverse government intervention or economic turmoil, high inflation and more volatile interest and currency exchange rates.

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 ACWISM, 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	+5.29%
Worst Quarter :	2Q '12	-8.94%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

5.29%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2012

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(8.94%)

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 ACWISM (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

16.80%

Since Inception

rr_AverageAnnualReturnSinceInception

16.75%

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

11.08%

Total annual operating expenses

rr_ExpensesOverAssets

12.33%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(10.93%)

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

2,988

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

7,886

Annual Return 2012

rr_AnnualReturn2012

5.50%

1 Year

rr_AverageAnnualReturnYear01

5.50%

Since Inception

rr_AverageAnnualReturnSinceInception

5.48%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2011

Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

5.50%

Since Inception

rr_AverageAnnualReturnSinceInception

5.48%

Investor Class | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

3.58%

Since Inception

rr_AverageAnnualReturnSinceInception

4.66%

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

3.07%

Total annual operating expenses

rr_ExpensesOverAssets

4.07%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(2.92%)

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

1,286

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

3,662

1 Year

rr_AverageAnnualReturnYear01

5.79%

Since Inception

rr_AverageAnnualReturnSinceInception

5.77%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2011

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Global 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.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Ariel Discovery Fund

Objective [Heading]

rr_ObjectiveHeading

Investment objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Ariel Discovery 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

2014-09-30

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 year, the Fund’s portfolio turnover rate was 33% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

33.00%

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Discovery 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, 2014.  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 Discovery Fund invests primarily in common stocks of companies with market capitalizations under $2 billion, measured at the time of initial purchase.  Over time, the market capitalizations for the Fund’s portfolio companies may change.

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.  As long as a portfolio company otherwise meets the Fund’s investment criteria and style, increased capitalization does not prevent the Fund from holding or buying more shares.

The Fund seeks to invest in companies which trade at low price-to-book ratios and have strong balance sheets.  The Fund only buys when Ariel believes these businesses are selling at deep discounts to their intrinsic value.

Individual company valuations will be based on assets and/or earnings power.  Flexibility in determining the proper valuation metric for a given company will be a key component of the Fund’s strategy.  We believe this approach creates a portfolio of well-researched stocks.  The Fund is managed on a dynamic basis as companies which approach fair value are likely to be sold and replaced by those with deeper discounts to intrinsic value.  The Fund may hold cash when values are difficult to identify.

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 Discovery Fund is a diversified fund that generally will not hold more than 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 cannotguarantee it will attain that objective.  You could lose money by investing in this Fund.  The principal risks are:

v Small 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. Small capitalization companies often have less predictable earnings, more limited product lines and markets and more limited financial and management resources.

v The general level of stock prices could decline.

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 :	1Q '12	+11.32%
Worst Quarter :	4Q '12	-1.98%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

11.32%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2012

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(1.98%)

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

S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

16.00%

Since Inception

rr_AverageAnnualReturnSinceInception

7.92%

Russell 2000 Value Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

18.05%

Since Inception

rr_AverageAnnualReturnSinceInception

5.85%

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

3.93%

Total annual operating expenses

rr_ExpensesOverAssets

5.18%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(3.68%)

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.50%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

153

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

471

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,577

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

4,324

Annual Return 2012

rr_AnnualReturn2012

15.65%

1 Year

rr_AverageAnnualReturnYear01

15.65%

Since Inception

rr_AverageAnnualReturnSinceInception

2.17%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2011

Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

15.65%

Since Inception

rr_AverageAnnualReturnSinceInception

2.17%

Investor Class | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

10.17%

Since Inception

rr_AverageAnnualReturnSinceInception

1.85%

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

3.78%

Total annual operating expenses

rr_ExpensesOverAssets

4.78%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(3.53%)

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.25%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

127

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

394

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,428

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

4,032

1 Year

rr_AverageAnnualReturnYear01

16.09%

^[2]

Since Inception

rr_AverageAnnualReturnSinceInception

16.05%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2011

^[2]

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Discovery Fund's total annual operating expenses to 1.50% of net assets for the Investor Class and 1.25% of net assets for Class I through the end of the fiscal year ending September 30, 2014. No termination of this agreement by either the Board of Trustees or the Adviser may be effective until, at the earliest, October 1, 2014.

[2] 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.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Feb. 01, 2013

XML

Ariel International Equity Fund | Ariel International Equity Fund

Ariel International Equity Fund

Investment objective

Ariel International Equity Fund pursues long-term capital appreciation.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel International Equity Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Minimum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel International Equity Fund		Investor Class	Institutional Class (Class I)
Management fees		1.00%	1.00%
Distribution and service (12b-1) fees		0.25%	none
Other expenses		15.75%	14.70%
Total annual operating expenses	[1]	17.00%	15.70%
Less fee waiver or expense reimbursement		(15.60%)	(14.55%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.40%	1.15%

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.

Expense Example Ariel International Equity Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	143	443	3,784	9,199
Institutional Class (Class I)	117	365	3,516	8,876

Portfolio turnover

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.

Principal investment strategy

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.

Principal risks

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.

Performance

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.

Total Return for the Year Ended December 31

Best Quarter :	4Q '12	+6.79%
Worst Quarter :	2Q '12	-11.41%

Average Annual Total Returns

Average Annual Returns Ariel International Equity Fund	1 Year	Since Inception	Inception Date
Investor Class	4.34%	4.32%	Dec. 30, 2011
Institutional Class (Class I)	4.60%	4.58%	Dec. 30, 2011
After Taxes on Distributions Investor Class	4.34%	4.32%
After Taxes on Distributions and Sales Investor Class	3.21%	3.84%
MSCI EAFE® Index (reflects no deductions for fees, expenses or taxes)	17.90%	17.85%

[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.

XML

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.

XML

Ariel Fund | Ariel Fund

Ariel Fund

Investment objective

Ariel Fund pursues long-term capital appreciation by investing in undervalued companies that show strong potential for growth.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Maximum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel Fund	Investor Class	Institutional Class (Class I)
Management fees	0.60%	0.60%
Distribution and service (12b-1) fees	0.25%	none
Other expenses	0.21%	0.08%
Total annual operating expenses	1.06%	0.68%

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.

Expense Example Ariel Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	108	337	585	1,294
Institutional Class (Class I)	69	218	379	847

Portfolio turnover

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.

Principal investment strategy

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.

Principal risks

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.

Performance

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.

Total Return for the Year Ended December 31

Best Quarter :	2Q '09	+34.75%
Worst Quarter :	4Q '08	-34.28%

Average Annual Total Returns

Average Annual Returns Ariel Fund		1 Year	5 Years	10 Years	Since Inception	Inception Date
Investor Class		20.32%	2.59%	6.87%	10.75%	Nov. 06, 1986
Institutional Class (Class I)	[1]	20.75%	2.66%	6.90%	10.76%	Nov. 06, 1986
After Taxes on Distributions Investor Class		20.15%	2.50%	6.41%	9.30%
After Taxes on Distributions and Sales Investor Class		13.43%	2.19%	5.99%	9.03%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		16.00%	1.66%	7.10%	9.46%
Russell 2500 Value Index (reflects no deductions for fees, expenses or taxes)		19.21%	4.54%	10.20%	11.03%
Russell 2000 Value Index (reflects no deductions for fees, expenses or taxes)		18.05%	3.55%	9.50%	10.33%

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).

[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.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Ariel Focus Fund

Objective [Heading]

rr_ObjectiveHeading

Investment objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Ariel Focus 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)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2014-09-30

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 year, the Fund’s portfolio turnover rate was 32% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

32.00%

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Focus 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, 2014.  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 Focus Fund invests primarily in common stocks of companies of any size in order to provide investors access to the best opportunities in companies of all market capitalizations.  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 invests primarily in high quality companies that are trading at low multiples of their actual or projected earnings.  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 Focus Fund is a non-diversified fund, which means that the Fund could own as few as 12 securities in its portfolio, and will generally own 25–30 securities.

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 of investing in the Fund are:

v As the Fund holds relatively few stocks, a fluctuation in one stock could significantly affect overall performance.

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.

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	+22.87%
Worst Quarter :	4Q '08	-26.82%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

22.87%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(26.82%)

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%

Since Inception

rr_AverageAnnualReturnSinceInception

4.62%

Russell 1000 Value Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

17.51%

5 Years

rr_AverageAnnualReturnYear05

0.59%

Since Inception

rr_AverageAnnualReturnSinceInception

3.79%

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

0.75%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.58%

Total annual operating expenses

rr_ExpensesOverAssets

1.58%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.33%)

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.25%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

127

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

432

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

796

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,821

Annual Return 2006

rr_AnnualReturn2006

11.58%

Annual Return 2007

rr_AnnualReturn2007

(2.54%)

Annual Return 2008

rr_AnnualReturn2008

(35.09%)

Annual Return 2009

rr_AnnualReturn2009

33.46%

Annual Return 2010

rr_AnnualReturn2010

11.13%

Annual Return 2011

rr_AnnualReturn2011

(5.21%)

Annual Return 2012

rr_AnnualReturn2012

11.42%

1 Year

rr_AverageAnnualReturnYear01

11.42%

5 Years

rr_AverageAnnualReturnYear05

0.33%

Since Inception

rr_AverageAnnualReturnSinceInception

2.10%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 2005

Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

11.22%

5 Years

rr_AverageAnnualReturnYear05

0.24%

Since Inception

rr_AverageAnnualReturnSinceInception

1.91%

Investor Class | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

7.68%

5 Years

rr_AverageAnnualReturnYear05

0.27%

Since Inception

rr_AverageAnnualReturnSinceInception

1.76%

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

0.75%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.54%

Total annual operating expenses

rr_ExpensesOverAssets

1.29%

^[1]

Less fee waiver or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.29%)

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.00%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

102

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

350

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

650

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,504

1 Year

rr_AverageAnnualReturnYear01

11.65%

^[2]

5 Years

rr_AverageAnnualReturnYear05

0.389%

^[2]

Since Inception

rr_AverageAnnualReturnSinceInception

2.13%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 2005

^[2]

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Focus Fund's total annual operating expenses to 1.25% of net assets for the Investor Class and 1.00% of net assets for Class I through the end of the fiscal year ending September 30, 2014. No termination of this agreement by either the Board of Trustees or the Adviser may be effective until, at the earliest, October 1, 2014.

[2] 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.

XML

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.

XML

Document and Entity Information	0 Months Ended
	Sep. 30, 2013
Risk/Return:
Document Type	485BPOS
Document Period End Date	Sep. 30, 2013
Registrant Name	ARIEL INVESTMENT TRUST
Central Index Key	0000798365
Amendment Flag	false
Document Creation Date	Jan. 28, 2013
Document Effective Date	Jan. 31, 2013
Prospectus Date	Feb. 01, 2013
Ariel Fund | Ariel Fund | Investor Class
Risk/Return:
Trading Symbol	ARGFX
Ariel Fund | Ariel Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	ARAIX
Ariel Appreciation Fund | Ariel Appreciation Fund | Investor Class
Risk/Return:
Trading Symbol	CAAPX
Ariel Appreciation Fund | Ariel Appreciation Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	CAAIX
Ariel Focus Fund | Ariel Focus Fund | Investor Class
Risk/Return:
Trading Symbol	ARFFX
Ariel Focus Fund | Ariel Focus Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	AFOYX
Ariel Discovery Fund | Ariel Discovery Fund | Investor Class
Risk/Return:
Trading Symbol	ARDFX
Ariel Discovery Fund | Ariel Discovery Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	ADYIX
Ariel International Equity Fund | Ariel International Equity Fund | Investor Class
Risk/Return:
Trading Symbol	AINTX
Ariel International Equity Fund | Ariel International Equity Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	AINIX
Ariel Global Equity Fund | Ariel Global Equity Fund | Investor Class
Risk/Return:
Trading Symbol	AGLOX
Ariel Global Equity Fund | Ariel Global Equity Fund | Institutional Class (Class I)
Risk/Return:
Trading Symbol	AGLYX

XML

Ariel Discovery Fund | Ariel Discovery Fund

Ariel Discovery Fund

Investment objective

Ariel Discovery Fund pursues long-term capital appreciation.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel Discovery Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Maximum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel Discovery Fund		Investor Class	Institutional Class (Class I)
Management fees		1.00%	1.00%
Distribution and service (12b-1) fees		0.25%	none
Other expenses		3.93%	3.78%
Total annual operating expenses	[1]	5.18%	4.78%
Less fee waiver or expense reimbursement		(3.68%)	(3.53%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.50%	1.25%

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Discovery 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, 2014.  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.

Expense Example Ariel Discovery Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	153	471	1,577	4,324
Institutional Class (Class I)	127	394	1,428	4,032

Portfolio turnover

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 33% of the average value of its portfolio.

Principal investment strategy

Ariel Discovery Fund invests primarily in common stocks of companies with market capitalizations under $2 billion, measured at the time of initial purchase.  Over time, the market capitalizations for the Fund’s portfolio companies may change.

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.  As long as a portfolio company otherwise meets the Fund’s investment criteria and style, increased capitalization does not prevent the Fund from holding or buying more shares.

The Fund seeks to invest in companies which trade at low price-to-book ratios and have strong balance sheets.  The Fund only buys when Ariel believes these businesses are selling at deep discounts to their intrinsic value.

Individual company valuations will be based on assets and/or earnings power.  Flexibility in determining the proper valuation metric for a given company will be a key component of the Fund’s strategy.  We believe this approach creates a portfolio of well-researched stocks.  The Fund is managed on a dynamic basis as companies which approach fair value are likely to be sold and replaced by those with deeper discounts to intrinsic value.  The Fund may hold cash when values are difficult to identify.

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 Discovery Fund is a diversified fund that generally will not hold more than 50 securities in its portfolio.

Principal risks

Although Ariel makes every effort to achieve the Fund’s objective of long-term capital appreciation, Ariel cannotguarantee it will attain that objective.  You could lose money by investing in this Fund.  The principal risks are:

v Small 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. Small capitalization companies often have less predictable earnings, more limited product lines and markets and more limited financial and management resources.

v The general level of stock prices could decline.

You should consider investing in the Fund if you are looking for long-term capital appreciation and are willing to accept the associated risks.

Performance

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.

Total Return for the Year Ended December 31

Best Quarter :	1Q '12	+11.32%
Worst Quarter :	4Q '12	-1.98%

Average Annual Total Returns

Average Annual Returns Ariel Discovery Fund		1 Year	Since Inception	Inception Date
Investor Class		15.65%	2.17%	Jan. 31, 2011
Institutional Class (Class I)	[1]	16.09%	16.05%	Jan. 31, 2011
After Taxes on Distributions Investor Class		15.65%	2.17%
After Taxes on Distributions and Sales Investor Class		10.17%	1.85%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		16.00%	7.92%
Russell 2000 Value Index (reflects no deductions for fees, expenses or taxes)		18.05%	5.85%

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Discovery Fund's total annual operating expenses to 1.50% of net assets for the Investor Class and 1.25% of net assets for Class I through the end of the fiscal year ending September 30, 2014. No termination of this agreement by either the Board of Trustees or the Adviser may be effective until, at the earliest, October 1, 2014.

[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.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Ariel Appreciation Fund

Objective [Heading]

rr_ObjectiveHeading

Investment objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Ariel Appreciation 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 28% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

28.00%

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Appreciation 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 Appreciation Fund invests primarily in common stocks of U.S. companies and the Fund generally will have a weighted average market capitalization between $2 billion and $15 billion.  The Fund will not hold stocks that fall within the top quintile 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 quintile, 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 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 Appreciation 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 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 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 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	+29.74%
Worst Quarter :	4Q '08	-29.88%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

29.74%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(29.88%)

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

8.57%

Russell Midcap Value Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

18.51%

5 Years

rr_AverageAnnualReturnYear05

3.79%

10 Years

rr_AverageAnnualReturnYear10

10.63%

Since Inception

rr_AverageAnnualReturnSinceInception

11.02%

Russell Midcap Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

17.28%

5 Years

rr_AverageAnnualReturnYear05

3.57%

10 Years

rr_AverageAnnualReturnYear10

10.65%

Since Inception

rr_AverageAnnualReturnSinceInception

10.72%

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

0.71%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.21%

Total annual operating expenses

rr_ExpensesOverAssets

1.17%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

119

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

372

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

644

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,420

Annual Return 2003

rr_AnnualReturn2003

30.97%

Annual Return 2004

rr_AnnualReturn2004

13.10%

Annual Return 2005

rr_AnnualReturn2005

2.92%

Annual Return 2006

rr_AnnualReturn2006

10.94%

Annual Return 2007

rr_AnnualReturn2007

(1.40%)

Annual Return 2008

rr_AnnualReturn2008

(40.74%)

Annual Return 2009

rr_AnnualReturn2009

62.96%

Annual Return 2010

rr_AnnualReturn2010

19.61%

Annual Return 2011

rr_AnnualReturn2011

(7.35%)

Annual Return 2012

rr_AnnualReturn2012

19.35%

1 Year

rr_AverageAnnualReturnYear01

19.35%

5 Years

rr_AverageAnnualReturnYear05

5.02%

10 Years

rr_AverageAnnualReturnYear10

7.86%

Since Inception

rr_AverageAnnualReturnSinceInception

10.24%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 01, 1989

Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

17.33%

5 Years

rr_AverageAnnualReturnYear05

4.14%

10 Years

rr_AverageAnnualReturnYear10

7.02%

Since Inception

rr_AverageAnnualReturnSinceInception

9.03%

Investor Class | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

15.00%

5 Years

rr_AverageAnnualReturnYear05

4.03%

10 Years

rr_AverageAnnualReturnYear10

6.73%

Since Inception

rr_AverageAnnualReturnSinceInception

8.76%

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

0.71%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.28%

Total annual operating expenses

rr_ExpensesOverAssets

0.99%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

101

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

315

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

547

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,213

1 Year

rr_AverageAnnualReturnYear01

19.62%

^[1]

5 Years

rr_AverageAnnualReturnYear05

5.06%

^[1]

10 Years

rr_AverageAnnualReturnYear10

7.88%

^[1]

Since Inception

rr_AverageAnnualReturnSinceInception

10.25%

^[1]

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 01, 1989

^[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.

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Ariel Focus Fund | Ariel Focus Fund

Ariel Focus Fund

Investment objective

Ariel Focus Fund pursues long-term capital appreciation by investing in undervalued companies that show strong potential for growth.

Fees and expenses of the Fund

The table below describes fees and expenses that you may pay if you buy and hold shares of the Fund.
 

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Ariel Focus Fund	Investor Class	Institutional Class (Class I)
Maximum sales charge (load) imposed on purchases	none	none
Maximum deferred sales charge (load)	none	none
Maximum sales charge (load) imposed on reinvested dividends	none	none
Redemption fees	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Ariel Focus Fund		Investor Class	Institutional Class (Class I)
Management fees		0.75%	0.75%
Distribution and service (12b-1) fees		0.25%	none
Other expenses		0.58%	0.54%
Total annual operating expenses	[1]	1.58%	1.29%
Less fee waiver or expense reimbursement		(0.33%)	(0.29%)
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.25%	1.00%

The example below illustrates the expenses you would pay on a $10,000 investment in Ariel Focus 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, 2014.  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.

Expense Example Ariel Focus Fund (USD $)	1-Year	3-Year	5-Year	10-Year
Investor Class	127	432	796	1,821
Institutional Class (Class I)	102	350	650	1,504

Portfolio turnover

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 32% of the average value of its portfolio.

Principal investment strategy

Ariel Focus Fund invests primarily in common stocks of companies of any size in order to provide investors access to the best opportunities in companies of all market capitalizations.  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 invests primarily in high quality companies that are trading at low multiples of their actual or projected earnings.  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 Focus Fund is a non-diversified fund, which means that the Fund could own as few as 12 securities in its portfolio, and will generally own 25–30 securities.

Principal risks

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 of investing in the Fund are:

v As the Fund holds relatively few stocks, a fluctuation in one stock could significantly affect overall performance.

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.

You should consider investing in the Fund if you are looking for long-term capital appreciation and are willing to accept the associated risks.

Performance

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.

Total Return for the Year Ended December 31

Best Quarter :	2Q '09	+22.87%
Worst Quarter :	4Q '08	-26.82%

Average Annual Total Returns

Average Annual Returns Ariel Focus Fund		1 Year	5 Years	Since Inception	Inception Date
Investor Class		11.42%	0.33%	2.10%	Jun. 30, 2005
Institutional Class (Class I)	[1]	11.65%	0.389%	2.13%	Jun. 30, 2005
After Taxes on Distributions Investor Class		11.22%	0.24%	1.91%
After Taxes on Distributions and Sales Investor Class		7.68%	0.27%	1.76%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		16.00%	1.66%	4.62%
Russell 1000 Value Index (reflects no deductions for fees, expenses or taxes)		17.51%	0.59%	3.79%

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).

[1] The Adviser is contractually obligated to waive fees or reimburse expenses in order to limit Ariel Focus Fund's total annual operating expenses to 1.25% of net assets for the Investor Class and 1.00% of net assets for Class I through the end of the fiscal year ending September 30, 2014. No termination of this agreement by either the Board of Trustees or the Adviser may be effective until, at the earliest, October 1, 2014.

[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.