Label	Element	Value
Oakmark International Small Cap Fund
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	ck0000872323_SupplementTextBlock	Harris Associates Investment Trust Oakmark International Small Cap Fund (the “Fund”) Supplement dated November 1, 2018 to the Fund’s Prospectus, Summary Prospectus, and Statement of Additional Information each dated January 26, 2018 Effective December 3, 2018, the Prospectus and Summary Prospectus are updated as follows:
Risk/Return [Heading]	rr_RiskReturnHeading	Oakmark International Small Cap Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table replaces the table under the subheading “Shareholder Fees” in the section titled “Fees and Expenses of the Fund”:
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Expense Example Closing [Text Block]	rr_ExpenseExampleClosingTextBlock	PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE.
Oakmark International Small Cap Fund \| Investor Class
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Exchange fee	rr_ExchangeFee	none
Oakmark International Small Cap Fund \| Advisor Class
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Exchange fee	rr_ExchangeFee	none
Oakmark International Small Cap Fund \| Institutional Class
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Exchange fee	rr_ExchangeFee	none
Oakmark International Small Cap Fund \| Service Class
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Exchange fee	rr_ExchangeFee	none

No definition available.

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- Definition

Exchange Fee includes the maximum fee charged for any exchange or transfer of interest from the Fund to another fund. The Fund may include in a footnote to the table, if applicable, a tabular presentation of the range of exchange fees or a narrative explanation of the fees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection table
-Paragraph 1
-Subparagraph 5

+ Details

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- Definition

The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection instructions
-Paragraph 4

+ Details

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- Definition

This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Include the narrative explanations in the order indicated. A Fund may modify the narrative explanations if the explanation contains comparable information to that shown. The narrative explanation regarding sales charge discounts is only required by a Fund that offers such discounts and should specify the minimum level of investment required to qualify for a discount. Modify the narrative explanation to state that Fund shares are sold on a national securities exchange at the end of the time periods indicated, and that brokerage commissions for buying and selling Fund shares through a broker are not reflected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection instructions
-Paragraph 1
-Subparagraph b

+ Details

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Maximum Deferred Sales Charge (Load) (as a percentage of ____) A.3.instructions.2.a.i "Maximum Deferred Sales Charge (Load)" includes the maximum total deferred sales charge (load) payable upon redemption, in installments, or both, expressed as a percentage of the amount or amounts stated in response to Item 7(a), except that, for a sales charge (load) based on net asset value at the time of purchase, show the sales charge (load) as a percentage of the offering price at the time of purchase. A Fund may include in a footnote to the table, if applicable, a tabular presentation showing the amount of deferred sales charges (loads) over time or a narrative explanation of the sales charges (loads) (e.g., __% in the first year after purchase, declining to __% in the __ year and eliminated thereafter). A.3.instructions.2.a.ii If more than one type of sales charge (load) is imposed (e.g., a deferred sales charge (load) and a front-end sales charge (load)), the first caption in the table should read "Maximum Sales Charge (Load)" and show the maximum cumulative percentage. Show the percentage amounts and the terms of each sales charge (load) comprising that figure on separate lines below.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection instructions
-Paragraph 2
-Subparagraph a
-Clause i

+ Details

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- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection table
-Paragraph 1
-Subparagraph 1

+ Details

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- References

No definition available.

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- Definition

Risk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicated

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 2

+ Details

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- Definition

Shareholder Fees (fees paid directly from your investment).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection table
-Paragraph 1

+ Details

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