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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Oct. 31, 2019
Entity Registrant Name dei_EntityRegistrantName Investment Managers Series Trust
Entity Central Index Key dei_EntityCentralIndexKey 0001318342
Amendment Flag dei_AmendmentFlag false
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Document Creation Date dei_DocumentCreationDate Feb. 27, 2020
Document Effective Date dei_DocumentEffectiveDate Mar. 01, 2020
Prospectus Date rr_ProspectusDate Mar. 01, 2020
Vaughan Nelson Emerging Markets Opportunities Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading SUMMARY SECTION – Vaughan Nelson Emerging Markets Opportunities Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The investment objective of the Vaughan Nelson Emerging Markets Opportunities Fund (the "Emerging Markets Opportunities Fund" or "Fund") is to seek long term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 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 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 48% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 48.00%
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates “Other Expenses” for Investor Class shares have been estimated for the current fiscal year.
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent “Other Expenses” for Institutional Class shares have been restated to reflect current fees.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This 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 in the Fund 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 remain the same. The example reflects the Fund's contractual fee waiver and/or expense reimbursement only for the term of the contractual fee waiver and/or expense reimbursement.

 

Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (including amounts borrowed for investment purposes) in equity securities of companies that are either listed, domiciled, or conduct a meaningful amount of business in emerging markets. The Fund's advisor defines companies conducting a meaningful amount of business in emerging markets as those companies that derive at least 50% of revenues or net profits from, or have at least 50% of assets or production capacities in, emerging market countries. The Fund's advisor also includes in the definition of emerging market companies those that have been organized under the laws of, have their principal offices or headquarters in, or the securities of which are principally traded in emerging market countries. Emerging market countries are those countries that are considered to be emerging markets or developing economies by the World Bank or the International Finance Corporation, or are included in any of Morgan Stanley Capital International (MSCI) emerging market indices. Emerging market countries are typically located in Asia, Africa, the Caribbean and Central America, South America, Eastern Europe, and the Middle East. While the Fund may invest in companies of any market capitalization, under normal market circumstances, the Fund expects to focus on small- and medium-sized companies with market capitalizations similar to companies included in the MSCI Emerging Markets SMID Cap Index (the "Index"). As of December 31, 2019, the Index included companies with market capitalizations between $34.7 million and $11.1 billion. From time to time, the Fund may have a significant portion of its assets in one or more market sectors.

 

The Fund's advisor uses a bottom-up approach, employing both fundamental research and quantitative tools, that seeks to identify companies with attractive valuations. The strategy invests in stocks that the Fund's advisor believes are profitable, undervalued based on a range of valuation metrics, including price to book, price to earnings and price to cash flow, and exhibit low levels of leverage. The Fund's investments in equity securities may include common stocks, preferred stocks, convertible securities and American, European and Global Depository Receipts ("ADRs," "EDRs," and "GDRs," respectively). ADRs are receipts that represent interests in foreign securities held on deposit by U.S. banks. EDRs and GDRs have the same qualities as ADRs, except that they may be traded in several international trading markets. The Fund may also invest in exchange-traded funds ("ETFs") that invest in portfolios of securities designed to track particular market segments or indices and whose shares are bought and sold on securities exchanges. The Fund generally will invest in securities of companies located in different countries and regions. From time to time, the Fund may have a significant portion of its assets invested in the securities of companies in one or a few countries or regions.
Risk [Heading] rr_RiskHeading Principal Risks of Investing
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Risk is inherent in all investing and you could lose money by investing in the Fund. A summary description of certain principal risks of investing in the Fund is set forth below. Before you decide whether to invest in the Fund, carefully consider these risk factors associated with investing in the Fund, which may cause investors to lose money. There can be no assurance that the Fund will achieve its investment objective.

 

Equity Risk. The value of the equity securities held by the Fund may fall due to general market and economic conditions, perceptions regarding the industries in which the issuers of securities held by the Fund participate, or factors relating to specific companies in which the Fund invests.

 

Emerging Market Risk. Many of the risks with respect to foreign investments are more pronounced for investments in issuers in developing or emerging market countries. Emerging market countries tend to have more government exchange controls, more volatile interest and currency exchange rates, less market regulation, and less developed economic, political and legal systems than those of more developed countries. In addition, emerging market countries may experience high levels of inflation and may have less liquid securities markets and less efficient trading and settlement systems.

 

Foreign Investment Risk. The prices of foreign securities may be more volatile than the prices of securities of U.S. issuers because of economic and social conditions abroad, political developments, and changes in the regulatory environments of foreign countries. In addition, changes in exchange rates and interest rates may adversely affect the values of the Fund's foreign investments. Foreign companies are generally subject to different legal and accounting standards than U.S. companies, and foreign financial intermediaries may be subject to less supervision and regulation than U.S. financial firms. Foreign securities include ADRs, EDRs and GDRs. Unsponsored ADRs and GDRs are organized independently and without the cooperation of the foreign issuer of the underlying securities, and involve additional risks because U.S. reporting requirements do not apply. In addition, the issuing bank may deduct shareholder distribution, custody, foreign currency exchange, and other fees from the payment of dividends.

 

Market Risk. The market price of a security or instrument may decline, sometimes rapidly or unpredictably, due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic or political conditions throughout the world, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. The market value of a security or instrument also may decline because of factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry.

 

Currency Risk. The values of investments in securities denominated in foreign currencies increase or decrease as the rates of exchange between those currencies and the U.S. Dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile and are affected by factors such as general economic conditions, the actions of the United States and foreign governments or central banks, the imposition of currency controls, and speculation.

 

Small-Cap and Mid-Cap Company Risk. The securities of small-capitalization and mid-capitalization companies may be subject to more abrupt or erratic market movements and may have lower trading volumes or more erratic trading than securities of larger, more established companies or market averages in general. In addition, such companies typically are more likely to be adversely affected than large capitalization companies by changes in earning results, business prospects, investor expectations or poor economic or market conditions.

 

Sector Focus Risk. The Fund may invest a larger portion of its assets in one or more sectors than many other mutual funds, and thus will be more susceptible to negative events affecting those sectors. For example, as of October 31, 2019, 20.86% of the Fund's total assets was invested in the financial sector. Performance of companies in the financial sector may be adversely impacted by many factors, including, among others: government regulations of, or related to, the sector; governmental monetary and fiscal policies; economic, business or political conditions; credit rating downgrades; changes in interest rates; price competition; and decreased liquidity in credit markets. This sector has experienced significant losses and a high degree of volatility in the recent past, and the impact of more stringent capital requirements and of recent or future regulation on any individual financial company or on the sector as a whole cannot be predicted.

 

ETF Risk. Investing in an ETF will provide the Fund with exposure to the securities comprising the index on which the ETF is based and will expose the Fund to risks similar to those of investing directly in those securities. Shares of ETFs typically trade on securities exchanges and may at times trade at a premium or discount to their net asset values. In addition, an ETF may not replicate exactly the performance of the benchmark index it seeks to track for a number of reasons, including transaction costs incurred by the ETF, the temporary unavailability of certain index securities in the secondary market or discrepancies between the ETF and the index with respect to the weighting of securities or the number of securities held. Investing in ETFs, which are investment companies, involves duplication of advisory fees and certain other expenses. The Fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs.

 

Management and Strategy Risk. The value of your investment depends on the judgment of the Fund's advisor about the quality, relative yield, value or market trends affecting a particular security, industry, sector or region, which may prove to be incorrect.

 

Value-Oriented Investment Strategies Risk. Value stocks are those that are believed to be undervalued in comparison to their peers due to adverse business developments or other factors. Value investing is subject to the risk that the market will not recognize a security's inherent value for a long time or at all, or that a stock judged to be undervalued may actually be appropriately priced or overvalued. In addition, during some periods (which may be extensive) value stocks generally may be out of favor in the markets.

 

Convertible Securities Risk. Convertible securities are subject to market and interest rate risk and credit risk. When the market price of the equity security underlying a convertible security decreases the convertible security tends to trade on the basis of its yield and other fixed income characteristics, and is more susceptible to credit and interest rate risks. When the market price of such equity security rises, the convertible security tends to trade on the basis of its equity conversion features and be more exposed to market risk. Convertible securities are typically issued by smaller capitalized companies with stock prices that may be more volatile than those of other companies.

 

Preferred Stock Risk. Preferred stock represents an equity interest in a company that generally entitles the holder to receive, in preference to the holders of other stocks such as common stock, dividends and a fixed share of the proceeds resulting from a liquidation of the company. The market value of preferred stock is subject to company-specific and market risks applicable generally to equity securities and is also sensitive to changes in the company's creditworthiness, the ability of the company to make payments on the preferred stock, and changes in interest rates, typically declining in value if interest rates rise.

 

Cybersecurity Risk. Cybersecurity incidents may allow an unauthorized party to gain access to Fund assets, customer data (including private shareholder information), or proprietary information, or cause the Fund, the Fund's advisor, and/or other service providers (including custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality. In an extreme case, a shareholder's ability to exchange or redeem Fund shares may be affected.
Risk Lose Money [Text] rr_RiskLoseMoney Risk is inherent in all investing and you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year for Institutional Class shares and by showing how the average annual total returns of Institutional Class shares of the Fund compare with the average annual total returns of a broad-based market index. Performance for classes other than those shown may vary from the performance shown to the extent the expenses for those classes differ. Updated performance information is available at the Fund's website, https://www.im.natixis.com/us/vaughan-nelson-funds. The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future. Effective October 1, 2019, Vaughan Nelson Investment Management, L.P. became investment advisor to the Fund. The performance shown for periods prior to October 1, 2019, is that of the Fund's previous advisor, Advisory Research, Inc.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year for Institutional Class shares and by showing how the average annual total returns of Institutional Class shares of the Fund compare with the average annual total returns of a broad-based market index.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress https://www.im.natixis.com/us/vaughan-nelson-funds
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar-Year Total Return (before taxes) for Institutional Class Shares For each calendar year at NAV
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Institutional Shares    
Highest Calendar Quarter Return at NAV 10.12% Quarter Ended 03/31/2017
Lowest Calendar Quarter Return at NAV (13.87)% Quarter Ended 09/30/2015

 
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns for periods ended December 31, 2019
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 Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Vaughan Nelson Emerging Markets Opportunities Fund | Investor Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol ADVKX
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Wire fee imst_WireFee $ 20
Overnight check delivery fee imst_OvernightCheckDeliveryFee 25
Retirement account fees (annual maintenance fee) rr_ShareholderFeeOther $ 15
Management fees rr_ManagementFeesOverAssets 1.00%
Distribution (Rule 12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses (includes shareholder service fees of up to 0.15%) rr_OtherExpensesOverAssets 0.79% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 2.04%
Fees waived and/or expenses reimbursed rr_FeeWaiverOrReimbursementOverAssets (0.44%) [2]
Total annual fund operating expenses after waiving fees and/or reimbursing expenses rr_NetExpensesOverAssets 1.60% [2]
One Year rr_ExpenseExampleYear01 $ 163
Three Years rr_ExpenseExampleYear03 597
Five Years rr_ExpenseExampleYear05 1,058
Ten Years rr_ExpenseExampleYear10 $ 2,334
1 Year rr_AverageAnnualReturnYear01 6.81%
5 Years rr_AverageAnnualReturnYear05 1.22%
Since Inception rr_AverageAnnualReturnSinceInception 0.73%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 01, 2013 [3]
Vaughan Nelson Emerging Markets Opportunities Fund | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol ADVMX
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Wire fee imst_WireFee $ 20
Overnight check delivery fee imst_OvernightCheckDeliveryFee 25
Retirement account fees (annual maintenance fee) rr_ShareholderFeeOther $ 15
Management fees rr_ManagementFeesOverAssets 1.00%
Distribution (Rule 12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses (includes shareholder service fees of up to 0.15%) rr_OtherExpensesOverAssets 0.79% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 1.79%
Fees waived and/or expenses reimbursed rr_FeeWaiverOrReimbursementOverAssets (0.44%) [2]
Total annual fund operating expenses after waiving fees and/or reimbursing expenses rr_NetExpensesOverAssets 1.35% [2]
One Year rr_ExpenseExampleYear01 $ 137
Three Years rr_ExpenseExampleYear03 521
Five Years rr_ExpenseExampleYear05 929
Ten Years rr_ExpenseExampleYear10 $ 2,069
Annual Return 2014 rr_AnnualReturn2014 (0.33%)
Annual Return 2015 rr_AnnualReturn2015 (10.66%)
Annual Return 2016 rr_AnnualReturn2016 10.27%
Annual Return 2017 rr_AnnualReturn2017 25.05%
Annual Return 2018 rr_AnnualReturn2018 (18.45%)
Annual Return 2019 rr_AnnualReturn2019 7.14%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Calendar Quarter Return at NAV
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2017
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.12%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Calendar Quarter Return at NAV
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.87%)
1 Year rr_AverageAnnualReturnYear01 7.14%
5 Years rr_AverageAnnualReturnYear05 1.48%
Since Inception rr_AverageAnnualReturnSinceInception 0.99%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 01, 2013 [3]
Vaughan Nelson Emerging Markets Opportunities Fund | After Taxes on Distributions | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 6.43% [4]
5 Years rr_AverageAnnualReturnYear05 0.93% [4]
Since Inception rr_AverageAnnualReturnSinceInception 0.23% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 01, 2013 [3],[4]
Vaughan Nelson Emerging Markets Opportunities Fund | After Taxes on Distributions and Sales | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 4.72% [4]
5 Years rr_AverageAnnualReturnYear05 1.12% [4]
Since Inception rr_AverageAnnualReturnSinceInception 0.60% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 01, 2013 [3],[4]
Vaughan Nelson Emerging Markets Opportunities Fund | MSCI Emerging Markets SMID Cap Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 12.37%
5 Years rr_AverageAnnualReturnYear05 3.43%
Since Inception rr_AverageAnnualReturnSinceInception 2.38%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 01, 2013 [3]
Vaughan Nelson International Small Cap Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading SUMMARY SECTION – Vaughan Nelson International Small Cap Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The investment objective of the Vaughan Nelson International Small Cap Fund (the "International Small Cap Fund" or "Fund") is to seek long term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 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 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 54% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 54.00%
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates “Other Expenses” for Investor Class shares have been estimated for the current fiscal year.
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent “Other Expenses” for Institutional Class shares have been restated to reflect current fees.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This 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 in the Fund 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 remain the same. The example reflects the Fund's contractual fee waiver and/or expense reimbursement only for the term of the contractual fee waiver and/or expense reimbursement.

 

Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (including amounts borrowed for investment purposes) in equity securities of small capitalization companies and will invest at least 75% of its net assets in securities of companies located outside of the United States. The Fund considers small capitalization companies to be companies with market capitalizations within the range of those companies included in the MSCI EAFE Small Cap Index at the time of purchase. Because small capitalization companies are defined by reference to an index, the range of market capitalization of companies in which the Fund invests may vary with market conditions. As of December 31, 2019, the market capitalizations of companies included in the MSCI EAFE Small Cap Index were between $196.1 million and $9.1 billion. Investments in companies that move above or below the capitalization range of the MSCI EAFE Small Cap Index may continue to be held by the Fund in the Fund advisor's sole discretion. From time to time, the Fund may have a significant portion of its assets in one or more market sectors.

 

The Fund's advisor uses a bottom-up approach, employing both fundamental research and quantitative tools, that seeks to identify companies with attractive valuations. The strategy invests in stocks that it believes are profitable, undervalued on a range of valuation metrics, and exhibit low levels of leverage. The Fund's investments in equity securities may include common stocks, preferred stocks, convertible securities and American, European and Global Depository Receipts ("ADRs," "EDRs," and "GDRs," respectively). ADRs are receipts that represent interests in foreign securities held on deposit by U.S. banks. EDRs and GDRs have the same qualities as ADRs, except that they may be traded in several international trading markets. The Fund may also invest in exchange-traded funds ("ETFs") that invest in portfolios of securities designed to track particular market segments or indices and whose shares are bought and sold on securities exchanges. The Fund invests primarily in equity securities of foreign (non-U.S.) companies located in developed countries but may also invest in emerging markets. The Fund generally will invest in securities of companies located in different countries and regions. From time to time, the Fund may have a significant portion of its assets invested in the securities of companies in one or a few countries or regions.
Risk [Heading] rr_RiskHeading Principal Risks of Investing
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Risk is inherent in all investing and you could lose money by investing in the Fund. A summary description of certain principal risks of investing in the Fund is set forth below. Before you decide whether to invest in the Fund, carefully consider these risk factors associated with investing in the Fund, which may cause investors to lose money. There can be no assurance that the Fund will achieve its investment objective.

 

Equity Risk. The value of the equity securities held by the Fund may fall due to general market and economic conditions, perceptions regarding the industries in which the issuers of securities held by the Fund participate, or factors relating to specific companies in which the Fund invests.

 

Small-Cap Company Risk. The securities of small-capitalization companies may be subject to more abrupt or erratic market movements and may have lower trading volumes or more erratic trading than securities of larger, more established companies or market averages in general. In addition, such companies typically are more likely to be adversely affected than large capitalization companies by changes in earning results, business prospects, investor expectations or poor economic or market conditions.

 

 

Foreign Investment Risk. The prices of foreign securities may be more volatile than the prices of securities of U.S. issuers because of economic and social conditions abroad, political developments, and changes in the regulatory environments of foreign countries. In addition, changes in exchange rates and interest rates may adversely affect the values of the Fund's foreign investments. Foreign companies are generally subject to different legal and accounting standards than U.S. companies, and foreign financial intermediaries may be subject to less supervision and regulation than U.S. financial firms. Foreign securities include ADRs, EDRs and GDRs. Unsponsored ADRs and GDRs are organized independently and without the cooperation of the foreign issuer of the underlying securities, and involve additional risks because U.S. reporting requirements do not apply. In addition, the issuing bank may deduct shareholder distribution, custody, foreign currency exchange, and other fees from the payment of dividends.

 

Market Risk. The market price of a security or instrument may decline, sometimes rapidly or unpredictably, due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic or political conditions throughout the world, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. The market value of a security or instrument also may decline because of factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry.

 

Geographic (Japan) Risk. From time to time, a significant portion of the Fund's total assets may be invested in the securities of Japanese companies. The growth of Japan's economy has historically lagged that of its Asian neighbors and other major developed economies. The Japanese economy is heavily dependent on international trade and has been adversely affected by trade tariffs, other protectionist measures, competition from emerging economies and the economic conditions of its trading partners. China has become an important trading partner with Japan, yet the countries' political relationship has become strained. Should political tension increase, it could adversely affect the economy, especially the export sector, and destabilize the region as a whole. Japan also remains heavily dependent on oil imports, and higher commodity prices could therefore have a negative impact on the economy.

 

Currency Risk. The values of investments in securities denominated in foreign currencies increase or decrease as the rates of exchange between those currencies and the U.S. Dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile and are affected by factors such as general economic conditions, the actions of the United States and foreign governments or central banks, the imposition of currency controls, and speculation.

 

Emerging Market Risk. Many of the risks with respect to foreign investments are more pronounced for investments in issuers in developing or emerging market countries. Emerging market countries tend to have more government exchange controls, more volatile interest and currency exchange rates, less market regulation, and less developed economic, political and legal systems than those of more developed countries. In addition, emerging market countries may experience high levels of inflation and may have less liquid securities markets and less efficient trading and settlement systems.

 

Sector Focus Risk. The Fund may invest a larger portion of its assets in one or more sectors than many other mutual funds, and thus will be more susceptible to negative events affecting those sectors. For example, as of October 31, 2019, 24.52% of the Fund's total assets was invested in the industrial sector. Performance of companies in the industrial sector may be adversely impacted by many factors, including, among others: worldwide economy growth, supply and demand for specific products and services, rapid technological developments and government regulations.

 

ETF Risk. Investing in an ETF will provide the Fund with exposure to the securities comprising the index on which the ETF is based and will expose the Fund to risks similar to those of investing directly in those securities. Shares of ETFs typically trade on securities exchanges and may at times trade at a premium or discount to their net asset values. In addition, an ETF may not replicate exactly the performance of the benchmark index it seeks to track for a number of reasons, including transaction costs incurred by the ETF, the temporary unavailability of certain index securities in the secondary market or discrepancies between the ETF and the index with respect to the weighting of securities or the number of securities held. Investing in ETFs, which are investment companies, involves duplication of advisory fees and certain other expenses. The Fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs.

 

 

Management and Strategy Risk. The value of your investment depends on the judgment of the Fund's advisor about the quality, relative yield, value or market trends affecting a particular security, industry, sector or region, which may prove to be incorrect.

 

Value-Oriented Investment Strategies Risk. Value stocks are those that are believed to be undervalued in comparison to their peers due to adverse business developments or other factors. Value investing is subject to the risk that the market will not recognize a security's inherent value for a long time or at all, or that a stock judged to be undervalued may actually be appropriately priced or overvalued. In addition, during some periods (which may be extensive) value stocks generally may be out of favor in the markets.

 

Convertible Securities Risk. Convertible securities are subject to market and interest rate risk and credit risk. When the market price of the equity security underlying a convertible security decreases the convertible security tends to trade on the basis of its yield and other fixed income characteristics, and is more susceptible to credit and interest rate risks. When the market price of such equity security rises, the convertible security tends to trade on the basis of its equity conversion features and be more exposed to market risk. Convertible securities are typically issued by smaller capitalized companies with stock prices that may be more volatile than those of other companies.

 

Preferred Stock Risk. Preferred stock represents an equity interest in a company that generally entitles the holder to receive, in preference to the holders of other stocks such as common stock, dividends and a fixed share of the proceeds resulting from a liquidation of the company. The market value of preferred stock is subject to company-specific and market risks applicable generally to equity securities and is also sensitive to changes in the company's creditworthiness, the ability of the company to make payments on the preferred stock, and changes in interest rates, typically declining in value if interest rates rise.

 

Cybersecurity Risk. Cybersecurity incidents may allow an unauthorized party to gain access to Fund assets, customer data (including private shareholder information), or proprietary information, or cause the Fund, the Fund's advisor, and/or other service providers (including custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality. In an extreme case, a shareholder's ability to exchange or redeem Fund shares may be affected.
Risk Lose Money [Text] rr_RiskLoseMoney Risk is inherent in all investing and you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year for Institutional Class shares and by showing how the average annual total returns of the Fund compare with the average annual total returns of a broad-based market index. Effective February 10, 2020, the Fund converted its existing Advisor Class shares to Institutional Class shares and the Advisor Class was then terminated. Institutional Class shares were first offered on December 31, 2013. For periods prior to December 31, 2013, the performance shown in the bar chart reflects the performance of Advisor Class shares. The returns shown in the bar chart have not been adjusted to reflect any differences in expenses between Advisor Class shares and Institutional Class shares; however, the Fund's Institutional Class shares would have had annual returns substantially similar to those of the Fund's former Advisor Class shares because they are invested in the same portfolio of securities and have a similar expense structure to that of the Advisor Class shares. Performance for classes other than those shown may vary from the performance shown to the extent the expenses for those classes differ. Updated performance information is available at the Fund's website, https://www.im.natixis.com/us/vaughan-nelson-funds. The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future. Effective October 1, 2019, Vaughan Nelson Investment Management, L.P. became investment advisor to the Fund. The performance shown for periods prior to October 1, 2019, is that of the Fund's previous advisor, Advisory Research, Inc.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year for Institutional Class shares and by showing how the average annual total returns of the Fund compare with the average annual total returns of a broad-based market index.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress https://www.im.natixis.com/us/vaughan-nelson-funds
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Return (before taxes) for Institutional Class Shares For each calendar year at NAV
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Institutional Class    
Highest Calendar Quarter Return at NAV 13.01% Quarter Ended 12/31/2019
Lowest Calendar Quarter Return at NAV (17.21)% Quarter Ended 09/30/2011

 
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns for periods ended December 31, 2019
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 Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Vaughan Nelson International Small Cap Fund | Investor Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol ADVJX
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Wire fee imst_WireFee $ 20
Overnight check delivery fee imst_OvernightCheckDeliveryFee 25
Retirement account fees (annual maintenance fee) rr_ShareholderFeeOther $ 15
Management fees rr_ManagementFeesOverAssets 0.90%
Distribution (Rule 12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses (includes shareholder service fees of up to 0.15%) rr_OtherExpensesOverAssets 1.19% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 2.34%
Fees waived and/or expenses reimbursed rr_FeeWaiverOrReimbursementOverAssets (0.94%) [5]
Total annual fund operating expenses after waiving fees and/or reimbursing expenses rr_NetExpensesOverAssets 1.40% [5]
One Year rr_ExpenseExampleYear01 $ 143
Three Years rr_ExpenseExampleYear03 640
Five Years rr_ExpenseExampleYear05 1,165
Ten Years rr_ExpenseExampleYear10 $ 2,604
1 Year rr_AverageAnnualReturnYear01 23.07%
5 Years rr_AverageAnnualReturnYear05 7.00%
Since Inception rr_AverageAnnualReturnSinceInception 7.28%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2010 [6]
Vaughan Nelson International Small Cap Fund | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol ADVLX
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Wire fee imst_WireFee $ 20
Overnight check delivery fee imst_OvernightCheckDeliveryFee 25
Retirement account fees (annual maintenance fee) rr_ShareholderFeeOther $ 15
Management fees rr_ManagementFeesOverAssets 0.90%
Distribution (Rule 12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses (includes shareholder service fees of up to 0.15%) rr_OtherExpensesOverAssets 1.19% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 2.09%
Fees waived and/or expenses reimbursed rr_FeeWaiverOrReimbursementOverAssets (0.94%) [5]
Total annual fund operating expenses after waiving fees and/or reimbursing expenses rr_NetExpensesOverAssets 1.15% [5]
One Year rr_ExpenseExampleYear01 $ 117
Three Years rr_ExpenseExampleYear03 564
Five Years rr_ExpenseExampleYear05 1,037
Ten Years rr_ExpenseExampleYear10 $ 2,346
Annual Return 2011 rr_AnnualReturn2011 (13.48%)
Annual Return 2012 rr_AnnualReturn2012 22.59%
Annual Return 2013 rr_AnnualReturn2013 23.06%
Annual Return 2014 rr_AnnualReturn2014 (2.82%)
Annual Return 2015 rr_AnnualReturn2015 (1.36%)
Annual Return 2016 rr_AnnualReturn2016 6.45%
Annual Return 2017 rr_AnnualReturn2017 29.52%
Annual Return 2018 rr_AnnualReturn2018 (15.38%)
Annual Return 2019 rr_AnnualReturn2019 23.41%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Calendar Quarter Return at NAV
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 13.01%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Calendar Quarter Return at NAV
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.21%)
1 Year rr_AverageAnnualReturnYear01 23.41%
5 Years rr_AverageAnnualReturnYear05 7.27%
Since Inception rr_AverageAnnualReturnSinceInception 7.57%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2010 [6]
Vaughan Nelson International Small Cap Fund | After Taxes on Distributions | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 22.92% [4]
5 Years rr_AverageAnnualReturnYear05 6.76% [4]
Since Inception rr_AverageAnnualReturnSinceInception 6.68% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2010 [4],[6]
Vaughan Nelson International Small Cap Fund | After Taxes on Distributions and Sales | Institutional Class Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 14.21% [4]
5 Years rr_AverageAnnualReturnYear05 5.82% [4]
Since Inception rr_AverageAnnualReturnSinceInception 6.03% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2010 [4],[6]
Vaughan Nelson International Small Cap Fund | MSCI EAFE Small Cap Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 24.96%
5 Years rr_AverageAnnualReturnYear05 8.85%
Since Inception rr_AverageAnnualReturnSinceInception 8.46%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2010 [6]
[1] “Other Expenses” for Institutional Class shares have been restated to reflect current fees. “Other Expenses” for Investor Class shares have been estimated for the current fiscal year. Actual expenses may differ from estimates.
[2] The Fund’s advisor has contractually agreed to waive its fees and/or pay for operating expenses of the Fund to ensure that total annual fund operating expenses (excluding any taxes, leverage interest, brokerage commissions, dividend and interest expenses on short sales, acquired fund fees and expenses (as determined in accordance with Form N-1A), expenses incurred in connection with any merger or reorganization, and extraordinary expenses such as litigation expenses) do not exceed 1.60% and 1.35% of the average daily net assets of the Investor Class shares and Institutional Class shares, respectively. This agreement is in effect until February 28, 2021, and it may be terminated before that date only by the Trust’s Board of Trustees. The Fund’s advisor is permitted to seek reimbursement from the Fund, subject to certain limitations, of fees waived or payments made to the Fund for a period ending three full fiscal years after the date of the waiver or payment. This reimbursement may be requested from the Fund if the reimbursement will not cause the Fund’s annual expense ratio to exceed the lesser of (a) the expense limitation in effect at the time such fees were waived or payments made, or (b) the expense limitation in effect at the time of the reimbursement.
[3] Investor Class shares were first offered on December 2, 2019. The performance figures for Investor Class shares include the performance for the Institutional Class shares for the period prior to December 2, 2019, adjusted for Investor Class shares’ expenses, which are higher than the expenses of Institutional Class shares.
[4] 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 Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
[5] The Fund's advisor has contractually agreed to waive its fees and/or pay for operating expenses of the Fund to ensure that total annual fund operating expenses (excluding any taxes, leverage interest, brokerage commissions, dividend and interest expenses on short sales, acquired fund fees and expenses (as determined in accordance with Form N-1A), expenses incurred in connection with any merger or reorganization, and extraordinary expenses such as litigation expenses) do not exceed 1.40% and 1.15% of the average daily net assets of the Investor Class shares and Institutional Class shares, respectively. This agreement is in effect until February 28, 2021, and it may be terminated before that date only by the Trust's Board of Trustees. The Fund's advisor is permitted to seek reimbursement from the Fund, subject to certain limitations, of fees waived or payments made to the Fund for a period ending three full fiscal years after the date of the waiver or payment. This reimbursement may be requested from the Fund if the reimbursement will not cause the Fund's annual expense ratio to exceed the lesser of (a) the expense limitation in effect at the time such fees were waived or payments made, or (b) the expense limitation in effect at the time of the reimbursement.
[6] Effective February 10, 2020, the Fund converted its existing Advisor Class shares to Institutional Class shares and the Advisor Class was then terminated. The Advisor Class shares (which were previously designated as Investor Class shares) were first offered on March 31, 2010. Institutional Class shares (which were previously designated as Class I shares) were first offered on December 31, 2013. The performance figures for Institutional Class shares include the performance for the Advisor Class shares for the period prior to December 31, 2013. Investor Class shares were first offered on December 2, 2019. The performance figures for Investor Class shares include the performance for the Institutional Class shares for the period prior to December 2, 2019, adjusted for Investor Class shares’ expenses, which are higher than the expenses of Institutional Class shares.