485BPOS

As filed with the Securities and Exchange Commission on February 12, 2020

1933 Act Registration No. 33-38953

1940 Act Registration No. 811-06279

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 x

Pre-Effective Amendment No.       o

Post-Effective Amendment No. 61 x

and/or

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940 x

Amendment No. 63                          x

(Check appropriate box or boxes)

HARRIS ASSOCIATES INVESTMENT TRUST

(Exact Name of Registrant as Specified in Charter)

111 S. Wacker Drive, Suite 4600

Chicago, Illinois 60606-4319

(Address of Principal Executive Offices)

Registrant’s Telephone Number, including Area Code: (312) 646-3600

Rana J. Wright

Harris Associates L.P.

111 S. Wacker Drive, Suite 4600

Chicago, Illinois 60606

(Name and Address of Agent for Service)

With copies to:

Ndenisarya M. Bregasi, Esq.

K&L Gates LLP

1601 K Street, N.W.

Washington, D.C.  20006-1600

Approximate Date of Proposed Public Offering: Continuous

It is proposed that this filing will become effective (check appropriate box):

x immediately upon filing pursuant to paragraph (b)

o on         pursuant to paragraph (b)

o 60 days after filing pursuant to paragraph (a)(1)

o on        pursuant to paragraph (a)(1)

o 75 days after filing pursuant to paragraph (a)(2)

o on         pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

o this post-effective amendment designates a new effective date for a previously filed post-effective amendment.

This amendment is being filed solely to submit in interactive data format exhibits containing risk/return summary information that is identical to the risk/return summary information contained in the Registrant’s prospectus for the following classes of the following funds, which was filed with the Securities and Exchange Commission in Post-Effective Amendment No. 60 to the Registrant’s registration statement on January 27, 2020:

Investor Class, Advisor Class, Institutional Class and Service Class Shares of Oakmark Fund, Oakmark Select Fund, Oakmark Equity and Income Fund, Oakmark Global Fund, Oakmark Global Select Fund, Oakmark International Fund and Oakmark International Small Cap Fund.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended (the “1933 Act”), and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirement for effectiveness of this registration statement under rule 485(b) under the 1933 Act and has duly caused this Post-Effective Amendment No. 61 to its Registration Statement on Form N-1A to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago and State of Illinois on February 12, 2020.

HARRIS ASSOCIATES INVESTMENT TRUST
By:	/s/ Kristi L. Rowsell
Name:	Kristi L. Rowsell
Title:	President

Pursuant to the requirements of the 1933 Act, Post-Effective Amendment No. 61 has been signed below by the following persons in the capacities indicated below on February 12, 2020.

Signature		Title
/s/ Thomas H. Hayden		Trustee
Thomas H. Hayden*
/s/ Hugh T. Hurley, III		Trustee
Hugh T. Hurley, III*
/s/ Patricia Louie		Trustee
Patricia Louie*
/s/ Christine M. Maki		Trustee
Christine M. Maki*
/s/Laurence C. Morse, Ph.D		Trustee
Laurence C. Morse, Ph.D*
/s/ Mindy M. Posoff		Trustee
Mindy M. Posoff*
/s/ Allan J. Reich		Trustee and Chair of the Board of Trustees
Allan J. Reich*
/s/ Steven S. Rogers		Trustee
Steven S. Rogers*
/s/ Kristi L. Rowsell		Trustee and President (Principal Executive Officer)
Kristi L. Rowsell
/s/ Zachary D. Weber		Principal Financial Officer
Zachary D. Weber
* By:	/s/ Kristi L. Rowsell
	Kristi L. Rowsell

*Attorney in Fact, pursuant to a power of attorney, filed with Post-Effective Amendment No. 60 to the Registrant’s Registration Statement on Form N-1A, File No. 33-38953, on January 27, 2020.

EXHIBIT INDEX

Exhibit Number	Description
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Total

Oakmark Global Select Fund

Oakmark Global Select Fund

INVESTMENT OBJECTIVE

Oakmark Global Select Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark Global Select Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		1.01%	1.01%	1.01%	1.01%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.24%	0.13%	0.07%	0.49%	[1]
Total Annual Fund Operating Expenses		1.25%	1.14%	1.08%	1.50%
Less: Fee waivers and/or expense reimbursements	[2]	0.07%	0.07%	0.07%	0.07%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		1.18%	1.07%	1.01%	1.43%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark Global Select Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 121	$ 109	$ 103	$ 146
3 Years	376	341	321	453
5 Years	651	592	556	783
10 Years	$ 1,435	$ 1,309	$ 1,233	$ 1,716

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 21% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in common stocks of U.S. and non-U.S. companies. The Fund invests in the securities of companies located in at least three countries. The Fund is non-diversified, which means that it may invest a greater portion of its assets in a more limited number of issuers than a diversified fund. The Fund could own as few as twelve securities, but generally will have approximately twenty securities in its portfolio and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry. Typically, the Fund will invest at least 40% of its total assets in securities of non-U.S. companies (unless the Adviser deems market conditions and/or company valuations less favorable to non-U.S. companies, in which case the Fund will invest at least 30% of its total assets in securities of non-U.S. companies). In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. There are no geographic limits on the Fund's non-U.S. investments, and the Fund may invest in securities of companies located in developed or emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. The Fund generally invests in the securities of larger capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Non-Diversification Risk. A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility.

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 18.6%, during the quarter ended March 31, 2012
• Lowest quarterly return: -18.1%, during the quarter ended December 31, 2018

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark Global Select Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	29.80%	6.78%	9.46%
Advisor Class	29.95%	none	none
Institutional Class	29.94%	none	none
After Taxes on Distributions | Investor Class	29.56%	5.97%	8.80%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	18.02%	5.30%	7.73%
MSCI World Index (Net) (does not reflect the deduction of fees, expenses or taxes)	27.67%	8.74%	9.47%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

[1] "Other expenses" are based on estimated amounts for the current fiscal year; actual expenses may vary.

[2] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.066% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Oakmark International Small Cap Fund

Risk/Return:

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Risk/Return [Heading]

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Oakmark International Small Cap Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Oakmark International Small Cap Fund seeks long-term capital appreciation.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment) None.

Operating Expenses Caption [Text]

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

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 39% of the average value of its portfolio.

Portfolio Turnover, Rate

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39.00%

Expense Example [Heading]

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Example.

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

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The Fund invests primarily in a diversified portfolio of common stocks of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including, its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in the stocks of "small cap companies." A small cap company is one whose market capitalization is no greater than the largest market capitalization of any company included in the S&P EPAC (Europe Pacific Asia Composite) Small Cap Index ($16.85 billion as of December 31, 2019).

The Fund may invest in non-U.S. markets throughout the world, including emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. Ordinarily, the Fund will invest in the securities of at least five countries outside the United States. There are no geographic limits on the Fund's non-U.S. investments.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to seventy stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Small Cap Securities Risk. Investments in small cap companies may be riskier than investments in larger, more established companies. The securities of smaller companies may trade less frequently and in smaller volumes, and as a result, may be less liquid than securities of larger companies. Therefore, when purchasing and selling smaller cap securities, the Fund may experience higher transactional costs due to the length of time that might be needed to purchase or sell such securities. Additionally, if the Fund is forced to sell securities to meet redemption requests or other cash needs, it may be forced to dispose of those securities under disadvantageous circumstances and at a loss. Smaller companies also may be more vulnerable to economic, market and industry changes. As a result, share price changes may be more sudden or erratic than the prices of other equity securities, especially over the short term. Because smaller companies may have limited product lines, markets or financial resources or may depend on a few key employees, they may be more susceptible to particular economic events or competitive factors than large capitalization companies.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to seventy rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Liquidity Risk. Trading markets or a particular investment in which the Fund is invested, including securities of smaller companies and securities of issuers located outside the United States, may become less liquid or even illiquid. Illiquid investments can be more difficult to purchase or sell at an advantageous price or time, and there is a greater risk that they may not be sold for the price at which the Fund is carrying them. The securities of smaller companies may trade less frequently and in smaller volumes, and as a result, may be less liquid than securities of larger companies. This risk may be heightened with investments in issuers located in developing and emerging countries. The inability to sell an investment can adversely affect the Fund's value or prevent the Fund from being able to take advantage of other investment opportunities.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category carries the risk that due to current market conditions, that category may be out of favor with investors.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 19.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -19.9%, during the quarter ended September 30, 2011

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.80%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.90%)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from foreign tax credits or any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from foreign tax credits or any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark International Small Cap Fund | MSCI World ex U.S. Small Cap Index (Net)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

25.41%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

8.17%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.04%

Oakmark International Small Cap Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.17%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.38%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 141

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

438

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

757

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,661

Annual Return 2010

rr_AnnualReturn2010

21.53%

Annual Return 2011

rr_AnnualReturn2011

(16.44%)

Annual Return 2012

rr_AnnualReturn2012

18.39%

Annual Return 2013

rr_AnnualReturn2013

27.68%

Annual Return 2014

rr_AnnualReturn2014

(7.72%)

Annual Return 2015

rr_AnnualReturn2015

0.74%

Annual Return 2016

rr_AnnualReturn2016

6.30%

Annual Return 2017

rr_AnnualReturn2017

26.08%

Annual Return 2018

rr_AnnualReturn2018

(23.73%)

Annual Return 2019

rr_AnnualReturn2019

31.90%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.90%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

6.32%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.76%

Oakmark International Small Cap Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.95%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.47%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.06%

Oakmark International Small Cap Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

19.04%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.94%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

5.44%

Oakmark International Small Cap Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.17%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.26%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 128

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

400

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

692

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,523

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

32.05%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark International Small Cap Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.17%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.06%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.23%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 126

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

392

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

678

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,493

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

32.01%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark International Small Cap Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.17%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.41%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.58%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 161

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

500

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

862

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,882

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.53%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

6.02%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.45%

XML

Label

Element

Value

Oakmark Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Oakmark Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Oakmark Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment) None.

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

Jan. 27, 2021

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 51% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

51.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in a diversified portfolio of common stocks of U.S. companies. The Fund generally invests in the securities of larger capitalization companies. The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Fund may also use options, including, but not limited to, buying and selling (writing) put and call options on individual stocks, when such use is desirable because of tax or other considerations.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Options Risk. The use of options involves investment strategies and risks different from those associated with ordinary portfolio securities transactions. If a strategy is applied at an inappropriate time or market conditions or trends are judged incorrectly, the use of options may lower the Fund's return. There can be no guarantee that the use of options will increase the Fund's return or income. In addition, there may be an imperfect correlation between the movement in prices of options and the securities underlying them and there may at times not be a liquid secondary market for various options.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 14.4%, during the quarter ended March 31, 2012
• Lowest quarterly return: -17.3%, during the quarter ended December 31, 2018

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.40%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2018

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(17.30%)

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Institutional Class Shares, and Advisor Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Institutional Class Shares, and Advisor Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark Fund | S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.49%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

11.70%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

13.56%

Oakmark Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.73%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.92%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.88%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 90

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

281

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

488

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,085

Annual Return 2010

rr_AnnualReturn2010

12.18%

Annual Return 2011

rr_AnnualReturn2011

1.82%

Annual Return 2012

rr_AnnualReturn2012

20.97%

Annual Return 2013

rr_AnnualReturn2013

37.29%

Annual Return 2014

rr_AnnualReturn2014

11.51%

Annual Return 2015

rr_AnnualReturn2015

(3.95%)

Annual Return 2016

rr_AnnualReturn2016

18.35%

Annual Return 2017

rr_AnnualReturn2017

21.14%

Annual Return 2018

rr_AnnualReturn2018

(12.73%)

Annual Return 2019

rr_AnnualReturn2019

26.98%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

26.98%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

8.82%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

12.43%

Oakmark Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

24.63%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

7.63%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

11.43%

Oakmark Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

17.61%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

6.84%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

10.24%

Oakmark Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.73%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.82%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.78%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 80

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

249

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

433

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 966

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.09%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.73%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.01%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.74%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.70%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 72

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

224

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

391

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 874

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.19%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.73%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.46%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.19%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

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

632

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,395

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

26.65%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

8.50%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

12.09%

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.043% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

XML

Label

Element

Value

Oakmark International Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Oakmark International Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Oakmark International Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment) None.

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

Jan. 27, 2021

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 35% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

35.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in a diversified portfolio of common stocks of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including, its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. The Fund may invest in non-U.S. markets throughout the world, including emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. Ordinarily, the Fund will invest in the securities of at least five countries outside of the United States. There are no geographic limits on the Fund's non-U.S. investments. The Fund may invest in securities of large-, mid-, and small- capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Liquidity Risk. Trading markets or a particular investment in which the Fund is invested, including securities of issuers located outside the United States, may become less liquid or even illiquid. Illiquid investments can be more difficult to purchase or sell at an advantageous price or time, and there is a greater risk that they may not be sold for the price at which the Fund is carrying them. This risk may be heightened with investments in issuers located in developing and emerging countries. The inability to sell an investment can adversely affect the Fund's value or prevent the Fund from being able to take advantage of other investment opportunities.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 16.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -20.4%, during the quarter ended September 30, 2011

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

16.80%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(20.40%)

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark International Fund | MSCI World ex U.S. Index (Net) (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

22.49%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.42%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

5.32%

Oakmark International Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.83%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.20%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.03%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.98%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 100

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

313

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

543

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,205

Annual Return 2010

rr_AnnualReturn2010

16.22%

Annual Return 2011

rr_AnnualReturn2011

(14.07%)

Annual Return 2012

rr_AnnualReturn2012

29.22%

Annual Return 2013

rr_AnnualReturn2013

29.34%

Annual Return 2014

rr_AnnualReturn2014

(5.41%)

Annual Return 2015

rr_AnnualReturn2015

(3.83%)

Annual Return 2016

rr_AnnualReturn2016

7.91%

Annual Return 2017

rr_AnnualReturn2017

29.75%

Annual Return 2018

rr_AnnualReturn2018

(23.43%)

Annual Return 2019

rr_AnnualReturn2019

24.21%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

24.21%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.07%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

7.30%

Oakmark International Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

23.97%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.39%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.67%

Oakmark International Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

15.00%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.05%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

5.96%

Oakmark International Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.83%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.12%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.95%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 92

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

286

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

496

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,103

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

24.33%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark International Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.83%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.03%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.86%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.81%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 83

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

259

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

449

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,001

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

24.43%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark International Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.83%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.46%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.29%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.24%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 126

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

394

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

682

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,501

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

23.92%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.76%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.95%

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.052% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

XML

Total

Oakmark Equity and Income Fund

Oakmark Equity and Income Fund

INVESTMENT OBJECTIVE

Oakmark Equity and Income Fund seeks income and preservation and growth of capital.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark Equity and Income Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		0.71%	0.71%	0.71%	0.71%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.20%	0.07%	0.02%	0.44%
Total Annual Fund Operating Expenses		0.91%	0.78%	0.73%	1.15%
Less: Fee waivers and/or expense reimbursements	[1]	0.10%	0.10%	0.10%	0.10%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		0.81%	0.68%	0.63%	1.05%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark Equity and Income Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 82	$ 70	$ 64	$ 107
3 Years	258	219	200	335
5 Years	448	380	349	581
10 Years	$ 999	$ 850	$ 781	$ 1,287

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 11% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of U.S. equity and debt securities (although the Fund may invest up to 35% of its total assets in equity and debt securities of non-U.S. issuers). The Fund is intended to present a balanced investment program between growth and income by investing approximately 40-75% of its total assets in common stock, including securities convertible into common stock, and up to 60% of its total assets in debt securities issued by the U.S. government or any of its agencies or instrumentalities (including agency mortgage-backed securities), non U.S. governments, and corporate entities rated at the time of purchase within the two highest ratings assigned by Moody's Investors Service, Inc. or by S&P Global Ratings, a division of S&P Global. The Fund may invest up to 20% of its total assets in unrated or below investment grade rated debt securities, commonly called junk bonds. The Fund may invest in the securities of large-, mid-, and small-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its equity investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry.

The proportion of the Fund held in debt securities will vary in light of the Adviser's view of the attractiveness of debt securities. In times when the Adviser believes equities provide above average absolute value, the proportion of the Fund allocated to debt securities will decline. In selecting debt securities, the Adviser considers many factors, including among other things, quality, yield-to-maturity, liquidity, current yield and call risk. The Adviser believes the role of fixed income investments in the Fund is to help buffer the volatility of the Fund's equity portfolio and generate income.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities.

Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks.

Debt Securities Risk. Debt securities are subject to credit risk, call risk, interest rate risk and liquidity risk.

Credit Risk. Credit risk is the risk the issuer or guarantor of a debt security will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

Call Risk. Upon the issuer's desire to call a security, or under other circumstances where a security is called, including when interest rates are low and issuers opt to repay the obligation underlying a "callable security" early, the Fund may have to reinvest the proceeds in an investment offering a lower yield and may not benefit from any increase in value that might otherwise result from declining interest rates.

Interest Rate Risk. The Fund's yield and share price will fluctuate in response to changes in interest rates and there is a risk of loss due to changes in interest rates. In general, the prices of debt securities rise when interest rates fall, and the prices fall when interest rates rise. The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates.

Liquidity Risk. Liquidity risk is the risk a particular security may be difficult to purchase or sell and that the Fund may be unable to sell such security at an advantageous time or price and may be forced to sell a security at a discount to the Adviser's estimated value of such a security.

U.S. Government Securities Risk. Some securities issued or guaranteed by U.S. government agencies or instrumentalities are not backed by the full faith and credit of the United States and may only be supported by the right of the agency or instrumentality to borrow from the U.S. Treasury. There can be no assurance that the U.S. government will always provide financial support to those agencies or instrumentalities.

Sovereign Debt Risk. Sovereign debt instruments, including U.S. and non-U.S. debt instruments, are subject to the risk that a governmental entity may delay, refuse, or be unable to pay interest or repay principal on its debt, due, for example, to cash flow problems, insufficient foreign currency reserves, political considerations, the size of the governmental entity's debt position in relation to the economy, its policy toward international lenders or the failure to put in place economic reforms required by multilateral agencies. If a governmental entity defaults, it may ask for more time in which to pay or for further loans. There is no legal process for collecting sovereign debt that a government does not pay, nor are there bankruptcy proceedings through which all or part of the sovereign debt that a government entity has not repaid may be collected.

Lower-Rated Debt Securities Risk. Below investment grade securities (commonly called junk bonds) are regarded as having predominately speculative characteristics with respect to the issuer's continuing ability to pay principal and interest and carry a greater risk that the issuer of such securities will default in the timely payment of principal and interest. Issuers of securities that are in default or have defaulted may fail to resume principal or interest payments, in which case the Fund may lose its entire investment.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Convertible Securities Risk. The value of a convertible security, which is a form of hybrid security (i.e., a security with both debt and equity characteristics), typically increases or decreases with the price of the underlying common stock. In general, a convertible security is subject to the market risks of stocks when the underlying stock's price is high relative to the conversion price and is subject to the market risks of debt securities when the underlying stock's price is low relative to the conversion price. The general market risks of debt securities that are common to convertible securities include, but are not limited to, interest rate risk and credit risk. Many convertible securities have credit ratings that are below investment grade and are subject to the same risks as an investment in lower-rated debt securities (commonly called junk bonds). To the extent the Fund invests in convertible securities issued by mid- or small-cap companies, it will be subject to the risks of investing in such companies.

Mortgage-Backed Securities Risk. In addition to being subject to the risks associated with investments in fixed-income securities generally (e.g., credit, liquidity and valuation risks), the values of mortgage-backed securities are influenced by the factors affecting the assets underlying the securities. The value of these securities may be significantly affected by changes in interest rates. These securities are also subject to the risk of default on the underlying mortgages, which may increase particularly during periods of market downturn. An unexpectedly high rate of defaults on the underlying assets will decrease the security's value. If borrowers pay back principal on mortgage-backed securities, before (prepayment) or after (extension) the market anticipates such payments, shortening or lengthening their duration, the Fund's performance could be impacted. In general, a mortgage-backed security might be called or otherwise converted, prepaid or redeemed before maturity due to an excess in cash flow to the issuer or due to a decline in interest rates. In the event there is a prepayment, the Fund would need to reinvest the proceeds, possibly in an investment offering a lower yield or interest rate. On the other hand, in general, slower payoffs or extension may occur if market interest rates rise, which has the effect of increasing the duration or interest rate risk of the impacted securities.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's annual average returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 9.0%, during the quarter ended December 31, 2011
• Lowest quarterly return: -12.8%, during the quarter ended September 30, 2011

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark Equity and Income Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	19.31%	5.79%	7.78%
Advisor Class	19.43%	none	none
Institutional Class	19.50%	none	none
Service Class	18.99%	5.49%	7.46%
After Taxes on Distributions | Investor Class	16.86%	3.99%	6.32%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	13.04%	4.31%	6.12%
Lipper Balanced Funds Index (does not reflect the deduction of fees, expenses or taxes)	19.44%	6.76%	8.12%
S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)	31.49%	11.70%	13.56%
Barclays U.S. Government/Credit Index (does not reflect the deduction of fees, expenses or taxes)	9.71%	3.23%	3.96%

The Lipper Balanced Fund Index measures the equal weighted performance of the 30 largest U.S. balanced funds as defined by Lipper. This index is unmanaged and investors cannot invest directly in this index. The S&P 500 Total Return Index is a float-adjusted, capitalization-weighted index of 500 U.S. large-capitalization stocks representing all major industries. It is a widely recognized index of broad U.S. equity market performance. Returns reflect the reinvestment of dividends. This index is unmanaged and investors cannot invest directly in this index. The Barclays U.S. Government / Credit Index measures the non-securitized component of the U.S. Aggregate Index. It includes investment grade, U.S. dollar-denominated, fixed-rate Treasuries, government-related and corporate securities. This index is unmanaged and investors cannot invest directly in this index. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.099% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Oakmark International Fund

Oakmark International Fund

INVESTMENT OBJECTIVE

Oakmark International Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark International Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		0.83%	0.83%	0.83%	0.83%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.20%	0.12%	0.03%	0.46%
Total Annual Fund Operating Expenses		1.03%	0.95%	0.86%	1.29%
Less: Fee waivers and/or expense reimbursements	[1]	0.05%	0.05%	0.05%	0.05%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		0.98%	0.90%	0.81%	1.24%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark International Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 100	$ 92	$ 83	$ 126
3 Years	313	286	259	394
5 Years	543	496	449	682
10 Years	$ 1,205	$ 1,103	$ 1,001	$ 1,501

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 35% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of common stocks of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including, its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. The Fund may invest in non-U.S. markets throughout the world, including emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. Ordinarily, the Fund will invest in the securities of at least five countries outside of the United States. There are no geographic limits on the Fund's non-U.S. investments. The Fund may invest in securities of large-, mid-, and small- capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Liquidity Risk. Trading markets or a particular investment in which the Fund is invested, including securities of issuers located outside the United States, may become less liquid or even illiquid. Illiquid investments can be more difficult to purchase or sell at an advantageous price or time, and there is a greater risk that they may not be sold for the price at which the Fund is carrying them. This risk may be heightened with investments in issuers located in developing and emerging countries. The inability to sell an investment can adversely affect the Fund's value or prevent the Fund from being able to take advantage of other investment opportunities.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 16.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -20.4%, during the quarter ended September 30, 2011

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark International Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	24.21%	5.07%	7.30%
Advisor Class	24.33%	none	none
Institutional Class	24.43%	none	none
Service Class	23.92%	4.76%	6.95%
After Taxes on Distributions | Investor Class	23.97%	4.39%	6.67%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	15.00%	4.05%	5.96%
MSCI World ex U.S. Index (Net) (does not reflect the deduction of fees, expenses or taxes)	22.49%	5.42%	5.32%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.052% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Oakmark Fund

Oakmark Fund

INVESTMENT OBJECTIVE

Oakmark Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		0.73%	0.73%	0.73%	0.73%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.19%	0.09%	0.01%	0.46%
Total Annual Fund Operating Expenses		0.92%	0.82%	0.74%	1.19%
Less: Fee waivers and/or expense reimbursements	[1]	0.04%	0.04%	0.04%	0.04%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		0.88%	0.78%	0.70%	1.15%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 90	$ 80	$ 72	$ 117
3 Years	281	249	224	365
5 Years	488	433	391	632
10 Years	$ 1,085	$ 966	$ 874	$ 1,395

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 51% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of common stocks of U.S. companies. The Fund generally invests in the securities of larger capitalization companies. The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Fund may also use options, including, but not limited to, buying and selling (writing) put and call options on individual stocks, when such use is desirable because of tax or other considerations.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Options Risk. The use of options involves investment strategies and risks different from those associated with ordinary portfolio securities transactions. If a strategy is applied at an inappropriate time or market conditions or trends are judged incorrectly, the use of options may lower the Fund's return. There can be no guarantee that the use of options will increase the Fund's return or income. In addition, there may be an imperfect correlation between the movement in prices of options and the securities underlying them and there may at times not be a liquid secondary market for various options.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 14.4%, during the quarter ended March 31, 2012
• Lowest quarterly return: -17.3%, during the quarter ended December 31, 2018

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	26.98%	8.82%	12.43%
Advisor Class	27.09%	none	none
Institutional Class	27.19%	none	none
Service Class	26.65%	8.50%	12.09%
After Taxes on Distributions | Investor Class	24.63%	7.63%	11.43%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	17.61%	6.84%	10.24%
S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)	31.49%	11.70%	13.56%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Institutional Class Shares, and Advisor Class Shares will vary from returns shown for Investor Class Shares.

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.043% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Label

Element

Value

Oakmark Equity and Income Fund

Risk/Return:

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Risk/Return [Heading]

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Oakmark Equity and Income Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Oakmark Equity and Income Fund seeks income and preservation and growth of capital.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment) None.

Operating Expenses Caption [Text]

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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

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Jan. 27, 2021

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 11% of the average value of its portfolio.

Portfolio Turnover, Rate

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11.00%

Expense Example [Heading]

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Example.

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

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The Fund invests primarily in a diversified portfolio of U.S. equity and debt securities (although the Fund may invest up to 35% of its total assets in equity and debt securities of non-U.S. issuers). The Fund is intended to present a balanced investment program between growth and income by investing approximately 40-75% of its total assets in common stock, including securities convertible into common stock, and up to 60% of its total assets in debt securities issued by the U.S. government or any of its agencies or instrumentalities (including agency mortgage-backed securities), non U.S. governments, and corporate entities rated at the time of purchase within the two highest ratings assigned by Moody's Investors Service, Inc. or by S&P Global Ratings, a division of S&P Global. The Fund may invest up to 20% of its total assets in unrated or below investment grade rated debt securities, commonly called junk bonds. The Fund may invest in the securities of large-, mid-, and small-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its equity investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry.

The proportion of the Fund held in debt securities will vary in light of the Adviser's view of the attractiveness of debt securities. In times when the Adviser believes equities provide above average absolute value, the proportion of the Fund allocated to debt securities will decline. In selecting debt securities, the Adviser considers many factors, including among other things, quality, yield-to-maturity, liquidity, current yield and call risk. The Adviser believes the role of fixed income investments in the Fund is to help buffer the volatility of the Fund's equity portfolio and generate income.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities.

Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks.

Debt Securities Risk. Debt securities are subject to credit risk, call risk, interest rate risk and liquidity risk.

Credit Risk. Credit risk is the risk the issuer or guarantor of a debt security will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

Call Risk. Upon the issuer's desire to call a security, or under other circumstances where a security is called, including when interest rates are low and issuers opt to repay the obligation underlying a "callable security" early, the Fund may have to reinvest the proceeds in an investment offering a lower yield and may not benefit from any increase in value that might otherwise result from declining interest rates.

Interest Rate Risk. The Fund's yield and share price will fluctuate in response to changes in interest rates and there is a risk of loss due to changes in interest rates. In general, the prices of debt securities rise when interest rates fall, and the prices fall when interest rates rise. The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates.

Liquidity Risk. Liquidity risk is the risk a particular security may be difficult to purchase or sell and that the Fund may be unable to sell such security at an advantageous time or price and may be forced to sell a security at a discount to the Adviser's estimated value of such a security.

U.S. Government Securities Risk. Some securities issued or guaranteed by U.S. government agencies or instrumentalities are not backed by the full faith and credit of the United States and may only be supported by the right of the agency or instrumentality to borrow from the U.S. Treasury. There can be no assurance that the U.S. government will always provide financial support to those agencies or instrumentalities.

Sovereign Debt Risk. Sovereign debt instruments, including U.S. and non-U.S. debt instruments, are subject to the risk that a governmental entity may delay, refuse, or be unable to pay interest or repay principal on its debt, due, for example, to cash flow problems, insufficient foreign currency reserves, political considerations, the size of the governmental entity's debt position in relation to the economy, its policy toward international lenders or the failure to put in place economic reforms required by multilateral agencies. If a governmental entity defaults, it may ask for more time in which to pay or for further loans. There is no legal process for collecting sovereign debt that a government does not pay, nor are there bankruptcy proceedings through which all or part of the sovereign debt that a government entity has not repaid may be collected.

Lower-Rated Debt Securities Risk. Below investment grade securities (commonly called junk bonds) are regarded as having predominately speculative characteristics with respect to the issuer's continuing ability to pay principal and interest and carry a greater risk that the issuer of such securities will default in the timely payment of principal and interest. Issuers of securities that are in default or have defaulted may fail to resume principal or interest payments, in which case the Fund may lose its entire investment.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Convertible Securities Risk. The value of a convertible security, which is a form of hybrid security (i.e., a security with both debt and equity characteristics), typically increases or decreases with the price of the underlying common stock. In general, a convertible security is subject to the market risks of stocks when the underlying stock's price is high relative to the conversion price and is subject to the market risks of debt securities when the underlying stock's price is low relative to the conversion price. The general market risks of debt securities that are common to convertible securities include, but are not limited to, interest rate risk and credit risk. Many convertible securities have credit ratings that are below investment grade and are subject to the same risks as an investment in lower-rated debt securities (commonly called junk bonds). To the extent the Fund invests in convertible securities issued by mid- or small-cap companies, it will be subject to the risks of investing in such companies.

Mortgage-Backed Securities Risk. In addition to being subject to the risks associated with investments in fixed-income securities generally (e.g., credit, liquidity and valuation risks), the values of mortgage-backed securities are influenced by the factors affecting the assets underlying the securities. The value of these securities may be significantly affected by changes in interest rates. These securities are also subject to the risk of default on the underlying mortgages, which may increase particularly during periods of market downturn. An unexpectedly high rate of defaults on the underlying assets will decrease the security's value. If borrowers pay back principal on mortgage-backed securities, before (prepayment) or after (extension) the market anticipates such payments, shortening or lengthening their duration, the Fund's performance could be impacted. In general, a mortgage-backed security might be called or otherwise converted, prepaid or redeemed before maturity due to an excess in cash flow to the issuer or due to a decline in interest rates. In the event there is a prepayment, the Fund would need to reinvest the proceeds, possibly in an investment offering a lower yield or interest rate. On the other hand, in general, slower payoffs or extension may occur if market interest rates rise, which has the effect of increasing the duration or interest rate risk of the impacted securities.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's annual average returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's annual average returns compare with those of a broad measure of market performance.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The Lipper Balanced Fund Index measures the equal weighted performance of the 30 largest U.S. balanced funds as defined by Lipper. This index is unmanaged and investors cannot invest directly in this index. The S&P 500 Total Return Index is a float-adjusted, capitalization-weighted index of 500 U.S. large-capitalization stocks representing all major industries. It is a widely recognized index of broad U.S. equity market performance. Returns reflect the reinvestment of dividends. This index is unmanaged and investors cannot invest directly in this index. The Barclays U.S. Government / Credit Index measures the non-securitized component of the U.S. Aggregate Index. It includes investment grade, U.S. dollar-denominated, fixed-rate Treasuries, government-related and corporate securities. This index is unmanaged and investors cannot invest directly in this index.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 9.0%, during the quarter ended December 31, 2011
• Lowest quarterly return: -12.8%, during the quarter ended September 30, 2011

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

9.00%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.80%)

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The Lipper Balanced Fund Index measures the equal weighted performance of the 30 largest U.S. balanced funds as defined by Lipper. This index is unmanaged and investors cannot invest directly in this index. The S&P 500 Total Return Index is a float-adjusted, capitalization-weighted index of 500 U.S. large-capitalization stocks representing all major industries. It is a widely recognized index of broad U.S. equity market performance. Returns reflect the reinvestment of dividends. This index is unmanaged and investors cannot invest directly in this index. The Barclays U.S. Government / Credit Index measures the non-securitized component of the U.S. Aggregate Index. It includes investment grade, U.S. dollar-denominated, fixed-rate Treasuries, government-related and corporate securities. This index is unmanaged and investors cannot invest directly in this index. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark Equity and Income Fund | Lipper Balanced Funds Index (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

19.44%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

6.76%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.12%

Oakmark Equity and Income Fund | S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.49%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

11.70%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

13.56%

Oakmark Equity and Income Fund | Barclays U.S. Government/Credit Index (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

9.71%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

3.23%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

3.96%

Oakmark Equity and Income Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.71%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.20%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.91%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.10%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.81%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 82

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

258

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

448

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 999

Annual Return 2010

rr_AnnualReturn2010

9.50%

Annual Return 2011

rr_AnnualReturn2011

0.64%

Annual Return 2012

rr_AnnualReturn2012

9.05%

Annual Return 2013

rr_AnnualReturn2013

24.25%

Annual Return 2014

rr_AnnualReturn2014

6.93%

Annual Return 2015

rr_AnnualReturn2015

(4.60%)

Annual Return 2016

rr_AnnualReturn2016

10.97%

Annual Return 2017

rr_AnnualReturn2017

14.46%

Annual Return 2018

rr_AnnualReturn2018

(8.33%)

Annual Return 2019

rr_AnnualReturn2019

19.31%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

19.31%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.79%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

7.78%

Oakmark Equity and Income Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

16.86%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

3.99%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.32%

Oakmark Equity and Income Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

13.04%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.31%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.12%

Oakmark Equity and Income Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.71%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.78%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.10%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.68%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 70

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

219

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

380

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 850

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

19.43%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Equity and Income Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.71%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.02%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.73%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.10%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.63%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 64

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

200

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

349

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 781

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

19.50%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Equity and Income Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.71%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.44%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.15%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.10%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 107

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

335

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

581

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,287

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

18.99%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.49%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

7.46%

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.099% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

XML

Label

Element

Value

Oakmark Select Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Oakmark Select Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Oakmark Select Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment) None.

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

Jan. 27, 2021

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 45% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

45.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in common stocks of U.S. companies. The Fund is non-diversified, which means that it may invest a greater portion of its assets in a more limited number of issuers than a diversified fund. The Fund could own as few as twelve securities, but generally will have approximately twenty securities in its portfolio and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry. The Fund generally invests in the securities of large- and mid-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Fund may also use options, including, but not limited to, buying and selling (writing) put and call options on individual stocks, when such use is desirable because of tax or other considerations.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Non-Diversification Risk. A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility and may lead to greater losses.

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large and medium) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Options Risk. The use of options involves investment strategies and risks different from those associated with ordinary portfolio securities transactions. If a strategy is applied at an inappropriate time or market conditions or trends are judged incorrectly, the use of options may lower the Fund's return. There can be no guarantee that the use of options will increase the Fund's return or income. In addition, there may be an imperfect correlation between the movement in prices of options and the securities underlying them and there may at times not be a liquid secondary market for various options.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

Risk Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility and may lead to greater losses.

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 15.6%, during the quarter ended March 31, 2012
• Lowest quarterly return: -21.7%, during the quarter ended December 31, 2018

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.60%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2018

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.70%)

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark Select Fund | S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

31.49%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

11.70%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

13.56%

Oakmark Select Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.88%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.07%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.00%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 102

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

319

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

554

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,228

Annual Return 2010

rr_AnnualReturn2010

13.24%

Annual Return 2011

rr_AnnualReturn2011

2.15%

Annual Return 2012

rr_AnnualReturn2012

21.74%

Annual Return 2013

rr_AnnualReturn2013

36.52%

Annual Return 2014

rr_AnnualReturn2014

15.39%

Annual Return 2015

rr_AnnualReturn2015

(3.58%)

Annual Return 2016

rr_AnnualReturn2016

15.31%

Annual Return 2017

rr_AnnualReturn2017

15.72%

Annual Return 2018

rr_AnnualReturn2018

(24.88%)

Annual Return 2019

rr_AnnualReturn2019

27.69%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.69%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.30%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

10.60%

Oakmark Select Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.48%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

3.58%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

9.61%

Oakmark Select Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

16.53%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

3.28%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.66%

Oakmark Select Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.88%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.05%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.93%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.86%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 88

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

276

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

479

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,066

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.82%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Select Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.88%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.01%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.89%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.82%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 84

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

263

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

457

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,017

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.87%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Select Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.88%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.42%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.30%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.23%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 126

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

392

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

678

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,494

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.40%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.00%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

10.27%

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.074% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Oakmark Select Fund

Oakmark Select Fund

INVESTMENT OBJECTIVE

Oakmark Select Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark Select Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		0.88%	0.88%	0.88%	0.88%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.19%	0.05%	0.01%	0.42%
Total Annual Fund Operating Expenses		1.07%	0.93%	0.89%	1.30%
Less: Fee waivers and/or expense reimbursements	[1]	0.07%	0.07%	0.07%	0.07%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		1.00%	0.86%	0.82%	1.23%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark Select Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 102	$ 88	$ 84	$ 126
3 Years	319	276	263	392
5 Years	554	479	457	678
10 Years	$ 1,228	$ 1,066	$ 1,017	$ 1,494

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 45% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in common stocks of U.S. companies. The Fund is non-diversified, which means that it may invest a greater portion of its assets in a more limited number of issuers than a diversified fund. The Fund could own as few as twelve securities, but generally will have approximately twenty securities in its portfolio and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular sector or industry. The Fund generally invests in the securities of large- and mid-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Fund may also use options, including, but not limited to, buying and selling (writing) put and call options on individual stocks, when such use is desirable because of tax or other considerations.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Non-Diversification Risk. A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility and may lead to greater losses.

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular sector or industry, changes affecting that sector or industry, or the perception of that sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large and medium) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Options Risk. The use of options involves investment strategies and risks different from those associated with ordinary portfolio securities transactions. If a strategy is applied at an inappropriate time or market conditions or trends are judged incorrectly, the use of options may lower the Fund's return. There can be no guarantee that the use of options will increase the Fund's return or income. In addition, there may be an imperfect correlation between the movement in prices of options and the securities underlying them and there may at times not be a liquid secondary market for various options.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 15.6%, during the quarter ended March 31, 2012
• Lowest quarterly return: -21.7%, during the quarter ended December 31, 2018

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark Select Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	27.69%	4.30%	10.60%
Advisor Class	27.82%	none	none
Institutional Class	27.87%	none	none
Service Class	27.40%	4.00%	10.27%
After Taxes on Distributions | Investor Class	27.48%	3.58%	9.61%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	16.53%	3.28%	8.66%
S&P 500 Index (does not reflect the deduction of fees, expenses or taxes)	31.49%	11.70%	13.56%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.074% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Oakmark International Small Cap Fund

Oakmark International Small Cap Fund

INVESTMENT OBJECTIVE

Oakmark International Small Cap Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark International Small Cap Fund	Investor Class	Advisor Class	Institutional Class	Service Class
Management fees	1.17%	1.17%	1.17%	1.17%
Distribution (12b-1) fees	none	none	none	none
Other expenses	0.21%	0.09%	0.06%	0.41%
Total Annual Fund Operating Expenses	1.38%	1.26%	1.23%	1.58%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark International Small Cap Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 141	$ 128	$ 126	$ 161
3 Years	438	400	392	500
5 Years	757	692	678	862
10 Years	$ 1,661	$ 1,523	$ 1,493	$ 1,882

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 39% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of common stocks of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including, its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in the stocks of "small cap companies." A small cap company is one whose market capitalization is no greater than the largest market capitalization of any company included in the S&P EPAC (Europe Pacific Asia Composite) Small Cap Index ($16.85 billion as of December 31, 2019).

The Fund may invest in non-U.S. markets throughout the world, including emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. Ordinarily, the Fund will invest in the securities of at least five countries outside the United States. There are no geographic limits on the Fund's non-U.S. investments.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to seventy stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Small Cap Securities Risk. Investments in small cap companies may be riskier than investments in larger, more established companies. The securities of smaller companies may trade less frequently and in smaller volumes, and as a result, may be less liquid than securities of larger companies. Therefore, when purchasing and selling smaller cap securities, the Fund may experience higher transactional costs due to the length of time that might be needed to purchase or sell such securities. Additionally, if the Fund is forced to sell securities to meet redemption requests or other cash needs, it may be forced to dispose of those securities under disadvantageous circumstances and at a loss. Smaller companies also may be more vulnerable to economic, market and industry changes. As a result, share price changes may be more sudden or erratic than the prices of other equity securities, especially over the short term. Because smaller companies may have limited product lines, markets or financial resources or may depend on a few key employees, they may be more susceptible to particular economic events or competitive factors than large capitalization companies.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to seventy rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Liquidity Risk. Trading markets or a particular investment in which the Fund is invested, including securities of smaller companies and securities of issuers located outside the United States, may become less liquid or even illiquid. Illiquid investments can be more difficult to purchase or sell at an advantageous price or time, and there is a greater risk that they may not be sold for the price at which the Fund is carrying them. The securities of smaller companies may trade less frequently and in smaller volumes, and as a result, may be less liquid than securities of larger companies. This risk may be heightened with investments in issuers located in developing and emerging countries. The inability to sell an investment can adversely affect the Fund's value or prevent the Fund from being able to take advantage of other investment opportunities.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category carries the risk that due to current market conditions, that category may be out of favor with investors.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 19.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -19.9%, during the quarter ended September 30, 2011

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark International Small Cap Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	31.90%	6.32%	6.76%
Advisor Class	32.05%	none	none
Institutional Class	32.01%	none	none
Service Class	31.53%	6.02%	6.45%
After Taxes on Distributions | Investor Class	31.95%	5.47%	6.06%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	19.04%	4.94%	5.44%
MSCI World ex U.S. Small Cap Index (Net)	25.41%	8.17%	8.04%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from foreign tax credits or any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

XML

Label

Element

Value

Oakmark Global Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Oakmark Global Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Oakmark Global Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment) None.

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

Jan. 27, 2021

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 20% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

20.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in a diversified portfolio of common stocks of U.S. and non-U.S. companies. The Fund invests in the securities of companies located in at least three countries. Typically, the Fund invests between 25-75% of its total assets in securities of U.S. companies and between 25-75% of its total assets in securities of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. There are no geographic limits on the Fund's non-U.S. investments, and the Fund may invest in securities of companies located in developed or emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. The Fund may invest in the securities of large-, mid-, and small-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in e1merging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund

RIsk Not Insured [Text]

rr_RiskNotInsured

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

Oakmark.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

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Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

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Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 15.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -18.3%, during the quarter ended September 30, 2011

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest quarterly return:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.80%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest quarterly return:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(18.30%)

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark Global Fund | MSCI World Index (Net) (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.67%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

8.74%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

9.47%

Oakmark Global Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.22%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.23%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.17%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 120

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

373

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

645

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,424

Annual Return 2010

rr_AnnualReturn2010

15.74%

Annual Return 2011

rr_AnnualReturn2011

(11.65%)

Annual Return 2012

rr_AnnualReturn2012

20.16%

Annual Return 2013

rr_AnnualReturn2013

34.12%

Annual Return 2014

rr_AnnualReturn2014

3.70%

Annual Return 2015

rr_AnnualReturn2015

(4.38%)

Annual Return 2016

rr_AnnualReturn2016

4.65%

Annual Return 2017

rr_AnnualReturn2017

27.08%

Annual Return 2018

rr_AnnualReturn2018

(18.97%)

Annual Return 2019

rr_AnnualReturn2019

29.60%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.60%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.96%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.60%

Oakmark Global Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

28.62%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.65%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

7.59%

Oakmark Global Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

18.44%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.56%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

6.91%

Oakmark Global Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.10%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.04%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 107

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

332

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

577

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,277

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.78%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Global Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.05%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.06%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.00%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 102

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

317

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

550

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,220

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.83%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Global Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.46%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.47%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.41%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 144

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

446

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

771

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,691

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.32%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.64%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.24%

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.059% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Jan. 28, 2020

XML

Total

Oakmark Global Fund

Oakmark Global Fund

INVESTMENT OBJECTIVE

Oakmark Global Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment) None.

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

Annual Fund Operating Expenses - Oakmark Global Fund		Investor Class	Advisor Class	Institutional Class	Service Class
Management fees		1.01%	1.01%	1.01%	1.01%
Distribution (12b-1) fees		none	none	none	none
Other expenses		0.22%	0.09%	0.05%	0.46%
Total Annual Fund Operating Expenses		1.23%	1.10%	1.06%	1.47%
Less: Fee waivers and/or expense reimbursements	[1]	0.06%	0.06%	0.06%	0.06%
Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements		1.17%	1.04%	1.00%	1.41%

Example.

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Expense Example - Oakmark Global Fund - USD ($)	Investor Class	Advisor Class	Institutional Class	Service Class
1 Year	$ 120	$ 107	$ 102	$ 144
3 Years	373	332	317	446
5 Years	645	577	550	771
10 Years	$ 1,424	$ 1,277	$ 1,220	$ 1,691

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 20% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of common stocks of U.S. and non-U.S. companies. The Fund invests in the securities of companies located in at least three countries. Typically, the Fund invests between 25-75% of its total assets in securities of U.S. companies and between 25-75% of its total assets in securities of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. There are no geographic limits on the Fund's non-U.S. investments, and the Fund may invest in securities of companies located in developed or emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. The Fund may invest in the securities of large-, mid-, and small-capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to sixty stocks rather than hundreds, and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to sixty rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in e1merging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large, medium or small) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies. Smaller companies may be more volatile due to, among other things, narrower product lines, more limited financial resources and fewer experienced managers. In addition, there is typically less publicly available information about such companies, and their stocks may have a more limited trading market than stocks of larger companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Investor Class Shares Total Returns for Years Ended December 31 (%)

Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 15.8%, during the quarter ended March 31, 2012
• Lowest quarterly return: -18.3%, during the quarter ended September 30, 2011

Average Annual Total Returns for Periods Ended December 31, 2019

Average Annual Returns - Oakmark Global Fund	Average Annual Returns, 1 Year	Average Annual Returns, 5 Years	Average Annual Returns, 10 Years
Investor Class	29.60%	5.96%	8.60%
Advisor Class	29.78%	none	none
Institutional Class	29.83%	none	none
Service Class	29.32%	5.64%	8.24%
After Taxes on Distributions | Investor Class	28.62%	4.65%	7.59%
After Taxes on Distributions and Sale of Fund Shares | Investor Class	18.44%	4.56%	6.91%
MSCI World Index (Net) (does not reflect the deduction of fees, expenses or taxes)	27.67%	8.74%	9.47%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.059% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

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Label

Element

Value

Oakmark Global Select Fund

Risk/Return:

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Risk/Return [Heading]

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Oakmark Global Select Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Oakmark Global Select Fund seeks long-term capital appreciation.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment) None.

Operating Expenses Caption [Text]

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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

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Jan. 27, 2021

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in 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 21% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

21.00%

Expense Example [Heading]

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Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGY

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in common stocks of U.S. and non-U.S. companies. The Fund invests in the securities of companies located in at least three countries. The Fund is non-diversified, which means that it may invest a greater portion of its assets in a more limited number of issuers than a diversified fund. The Fund could own as few as twelve securities, but generally will have approximately twenty securities in its portfolio and as a result, a higher percentage of the Fund's total assets may at times be invested in a particular region, sector or industry. Typically, the Fund will invest at least 40% of its total assets in securities of non-U.S. companies (unless the Adviser deems market conditions and/or company valuations less favorable to non-U.S. companies, in which case the Fund will invest at least 30% of its total assets in securities of non-U.S. companies). In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. There are no geographic limits on the Fund's non-U.S. investments, and the Fund may invest in securities of companies located in developed or emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. The Fund generally invests in the securities of larger capitalization companies.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of the company's intrinsic value. By "intrinsic value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is a company's intrinsic value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that have discounted stock prices compared to what the Adviser believes are the companies' intrinsic values. In assessing such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1.  Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2.  Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3.  Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated intrinsic value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the United States or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks can significantly affect the Fund's performance:

Non-Diversification Risk. A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility.

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value and public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. Investments in securities issued by entities domiciled in the United States also may be subject to many of these risks. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category (large) carries the risk that due to current market conditions, that category may be out of favor with investors. Larger, more established companies may be unable to respond quickly to new competitive challenges or opportunities or attain the high growth rate of successful smaller companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' intrinsic values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

Risk Lose Money [Text]

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You may lose money by investing in the Fund

Risk Nondiversified Status [Text]

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A non-diversified fund (generally, a fund that may invest in a limited number of issuers) may be subject to greater risk than a diversified fund because changes in the financial condition or market assessment of a single issuer may cause greater fluctuation in the value of a non-diversified Fund's shares. Lack of broad diversification also may cause a non-diversified fund to be more susceptible to economic, political or regulatory events than a diversified fund. A non-diversification strategy may increase the Fund's volatility.

RIsk Not Insured [Text]

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Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available on Oakmark.com or by calling 1-800-OAKMARK (625-6275).

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance.

Performance Availability Phone [Text]

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1-800-OAKMARK (625-6275)

Performance Availability Website Address [Text]

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Oakmark.com

Performance Past Does Not Indicate Future [Text]

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The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future.

Bar Chart [Heading]

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Investor Class Shares Total Returns for Years Ended December 31 (%)

Bar Chart Closing [Text Block]

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Since 2010, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:
• Highest quarterly return: 18.6%, during the quarter ended March 31, 2012
• Lowest quarterly return: -18.1%, during the quarter ended December 31, 2018

Highest Quarterly Return, Label

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Highest quarterly return:

Highest Quarterly Return, Date

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Mar. 31, 2012

Highest Quarterly Return

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18.60%

Lowest Quarterly Return, Label

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Lowest quarterly return:

Lowest Quarterly Return, Date

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Dec. 31, 2018

Lowest Quarterly Return

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(18.10%)

Index No Deduction for Fees, Expenses, Taxes [Text]

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(does not reflect the deduction of fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

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After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Performance Table Explanation after Tax Higher

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In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Closing [Text Block]

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

Average Annual Return, Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns for Periods Ended December 31, 2019

Oakmark Global Select Fund | MSCI World Index (Net) (does not reflect the deduction of fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

27.67%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

8.74%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

9.47%

Oakmark Global Select Fund | Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.24%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.25%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.18%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 121

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

376

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

651

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,435

Annual Return 2010

rr_AnnualReturn2010

11.06%

Annual Return 2011

rr_AnnualReturn2011

(5.87%)

Annual Return 2012

rr_AnnualReturn2012

23.95%

Annual Return 2013

rr_AnnualReturn2013

33.80%

Annual Return 2014

rr_AnnualReturn2014

2.57%

Annual Return 2015

rr_AnnualReturn2015

1.85%

Annual Return 2016

rr_AnnualReturn2016

9.93%

Annual Return 2017

rr_AnnualReturn2017

21.18%

Annual Return 2018

rr_AnnualReturn2018

(21.19%)

Annual Return 2019

rr_AnnualReturn2019

29.80%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.80%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

6.78%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

9.46%

Oakmark Global Select Fund | Investor Class | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.56%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.97%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

8.80%

Oakmark Global Select Fund | Investor Class | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

18.02%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

5.30%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

7.73%

Oakmark Global Select Fund | Advisor Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.13%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.14%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.07%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 109

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

341

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

592

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,309

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.95%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Global Select Fund | Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.08%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.01%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 103

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

321

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

556

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,233

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

29.94%

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

none

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

none

Oakmark Global Select Fund | Service Class

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

1.01%

Distribution (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.49%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.50%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

0.07%

^[1]

Total Annual Fund Operating Expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.43%

Other Expenses, New Fund, Based on Estimates [Text]

rr_OtherExpensesNewFundBasedOnEstimates

"Other expenses" are based on estimated amounts for the current fiscal year; actual expenses may vary.

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 146

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

453

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

783

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,716

[1] Harris Associates L.P. (the "Adviser") has contractually agreed to waive 0.066% of its management fee otherwise payable to it by the Fund through January 27, 2021. This arrangement may only be modified or amended with approval from the Fund and the Adviser.

[2] "Other expenses" are based on estimated amounts for the current fiscal year; actual expenses may vary.

XML

Document and Entity Information	Total
Prospectus:
Document Type	485BPOS
Document Period End Date	Sep. 30, 2019
Registrant Name	HARRIS ASSOCIATES INVESTMENT TRUST
Entity Central Index Key	0000872323
Entity Inv Company Type	N-1A
Amendment Flag	false
Document Creation Date	Jan. 27, 2020
Document Effective Date	Jan. 28, 2020
Prospectus Date	Jan. 28, 2020
Oakmark Fund | Institutional Class
Prospectus:
Trading Symbol	OANMX
Oakmark Fund | Advisor Class
Prospectus:
Trading Symbol	OAYMX
Oakmark Fund | Service Class
Prospectus:
Trading Symbol	OARMX
Oakmark Fund | Investor Class
Prospectus:
Trading Symbol	OAKMX
Oakmark Select Fund | Institutional Class
Prospectus:
Trading Symbol	OANLX
Oakmark Select Fund | Advisor Class
Prospectus:
Trading Symbol	OAYLX
Oakmark Select Fund | Service Class
Prospectus:
Trading Symbol	OARLX
Oakmark Select Fund | Investor Class
Prospectus:
Trading Symbol	OAKLX
Oakmark Equity and Income Fund | Institutional Class
Prospectus:
Trading Symbol	OANBX
Oakmark Equity and Income Fund | Advisor Class
Prospectus:
Trading Symbol	OAYBX
Oakmark Equity and Income Fund | Service Class
Prospectus:
Trading Symbol	OARBX
Oakmark Equity and Income Fund | Investor Class
Prospectus:
Trading Symbol	OAKBX
Oakmark Global Fund | Institutional Class
Prospectus:
Trading Symbol	OANGX
Oakmark Global Fund | Advisor Class
Prospectus:
Trading Symbol	OAYGX
Oakmark Global Fund | Service Class
Prospectus:
Trading Symbol	OARGX
Oakmark Global Fund | Investor Class
Prospectus:
Trading Symbol	OAKGX
Oakmark Global Select Fund | Institutional Class
Prospectus:
Trading Symbol	OANWX
Oakmark Global Select Fund | Advisor Class
Prospectus:
Trading Symbol	OAYWX
Oakmark Global Select Fund | Service Class
Prospectus:
Trading Symbol	OARWX
Oakmark Global Select Fund | Investor Class
Prospectus:
Trading Symbol	OAKWX
Oakmark International Fund | Advisor Class
Prospectus:
Trading Symbol	OAYIX
Oakmark International Fund | Institutional Class
Prospectus:
Trading Symbol	OANIX
Oakmark International Fund | Service Class
Prospectus:
Trading Symbol	OARIX
Oakmark International Fund | Investor Class
Prospectus:
Trading Symbol	OAKIX
Oakmark International Small Cap Fund | Institutional Class
Prospectus:
Trading Symbol	OANEX
Oakmark International Small Cap Fund | Advisor Class
Prospectus:
Trading Symbol	OAYEX
Oakmark International Small Cap Fund | Service Class
Prospectus:
Trading Symbol	OAREX
Oakmark International Small Cap Fund | Investor Class
Prospectus:
Trading Symbol	OAKEX