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Loomis Sayles Small Cap Value Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Small Cap Value Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund’s investment objective is long-term capital growth from investments in common stocks or other equity securities.
Expense [Heading] rr_ExpenseHeading FUND FEES & EXPENSES
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund.  You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in this table.
The Fund does not impose a sales charge, a redemption fee or an exchange fee.
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 January 31, 2026
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 for you if your 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 its most recently ended fiscal year, the Fund’s portfolio turnover rate was 25% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 25.00%
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 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, except that the examples are based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading INVESTMENTS, RISKS AND PERFORMANCE Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Fund normally will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in the equity securities of “small-cap companies,” including preferred stocks, warrants, securities convertible into common or preferred stocks and other equity-like interests in an entity. Currently, the Fund defines a small-cap company to be one whose market capitalization falls within the capitalization range of the Russell 2000® Index, an index that tracks stocks of 2,000 of the smallest U.S. companies. The Fund may invest the rest of its assets in companies of any size, including large-capitalization companies.
In deciding which securities to buy and sell, Loomis Sayles seeks to identify securities of smaller companies that it believes are undervalued by the market using a disciplined bottom-up approach to investing. Utilizing fundamental research, Loomis Sayles seeks to identify those stocks selling at a discount to its assessment of intrinsic value. The Fund’s investments focus on market inefficiencies and may include companies that are misunderstood by other investors; are undergoing a change in the business model or financial structure; or those companies that are not yet well-known to the investment community but are considered to have favorable fundamental prospects and attractive valuation. The portfolio managers analyze fundamental trends across the various industries in the sectors and use this information along with security valuation procedures to determine which stocks they believe are best positioned to outperform the industry or sector. Sell decisions are made when there is a deterioration in fundamentals, a stock reaches a target price or a more attractive opportunity is found.
The Fund may invest up to 20% of its assets in foreign securities, including emerging markets securities. Although certain equity securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if they are included in the U.S. equity indices published by S&P Global Ratings or Russell Investments. The Fund may also invest in real estate investment trusts (“REITs”), securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”) and other privately placed investments such as private equity investments and, to the extent permitted by the Investment Company Act of 1940, and the rules thereunder (the “1940 Act”), investment companies. The Fund may engage, for hedging and investment purposes, in foreign currency transactions (such as forward currency contracts), options and futures transactions.
Risk [Heading] rr_RiskHeading Principal Risks
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Risk/Return Bar Chart and Table
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and additional indices that represent the market sectors in which the Fund primarily invests. The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated performance information is available online at www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330.
To the extent that a class of shares was subject to the waiver or reimbursement of certain expenses during a period, had such expenses not been waived or reimbursed during the period, total returns would have been lower.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and additional indices that represent the market sectors in which the Fund primarily invests.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Total Returns for Institutional Class Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Highest Quarterly Return:Fourth Quarter 2020, 27.47%Lowest Quarterly Return:First Quarter 2020, -33.76%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns(for the periods ended December 31, 2024)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for 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 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-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
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-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts. The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes.
Loomis Sayles Small Cap Value Fund | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock You may lose money by investing in the Fund.
Loomis Sayles Small Cap Value Fund | Risk Not Insured [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Fund shares are not bank deposits and are not guaranteed, endorsed or insured by the Federal Deposit Insurance Corporation or any other government agency, and are subject to investment risks, including possible loss of the principal invested.
Loomis Sayles Small Cap Value Fund | Credit Counterparty Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Credit/Counterparty Risk is the risk that the issuer or guarantor of a fixed-income security in which the Fund invests, or the counterparty to a derivative or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. As a result, the Fund may sustain losses or be unable or delayed in its ability to realize gains.
Loomis Sayles Small Cap Value Fund | Currency Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Currency Risk is the risk that the value of the Fund’s investments will fall as a result of changes in exchange rates. Loomis Sayles may elect not to hedge currency risk or may hedge imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.
Loomis Sayles Small Cap Value Fund | Market Issuer Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market/Issuer Risk is the risk that the market value of the Fund’s investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund’s investments, such as management performance, financial condition and demand for the issuers’ goods and services.
Loomis Sayles Small Cap Value Fund | Cybersecurity and Technology Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Cybersecurity and Technology Risk is the risk associated with the increasing dependence of the Fund, its service providers, and other market participants on complex information technology and communications systems. Such systems are subject to a number of different threats and risks that could adversely affect the Fund and its shareholders. Cybersecurity and other operational and technology issues may result in financial losses to the Fund and its shareholders.
Loomis Sayles Small Cap Value Fund | Derivatives Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, options and futures transactions will fall, for example, because of changes in the value of the underlying reference instruments, pricing difficulties or lack of correlation with the underlying investments. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. There is also the risk that the Fund may be unable to terminate or sell a derivative position at an advantageous time or price.  The Fund’s derivative counterparties may experience financial difficulties or otherwise be unwilling or unable to honor their obligations, possibly resulting in losses to the Fund.  This risk is greater for forward currency contracts and other OTC traded derivatives. Investing in derivatives gives rise to other risks, such as leverage risk, liquidity risk, credit/counterparty risk, interest rate risk and market/issuer risk. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used.
Loomis Sayles Small Cap Value Fund | Emerging Markets Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Emerging Markets Risk is the risk that the Fund’s investments in emerging markets may face greater foreign securities risk. Emerging markets investments are subject to greater risks arising from political or economic instability, war, nationalization or confiscatory taxation, currency exchange or repatriation restrictions, sanctions by other countries (such as the United States or the European Union), new or inconsistent government treatment of or restrictions on issuers and instruments, and an issuer’s unwillingness or inability to make dividend, principal or interest payments on its securities. Emerging markets companies may be smaller and have shorter operating histories than companies in developed markets.
Loomis Sayles Small Cap Value Fund | Equity Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Equity Securities Risk is the risk that the value of a stock may decline for a number of reasons that relate directly to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods and services, or the equity markets generally.  Value stocks can perform differently from the market as a whole and from other types of stocks. Value stocks also present the risk that their lower valuations fairly reflect their business prospects and that investors will not agree that the stocks represent favorable investment opportunities, and they may fall out of favor with investors and underperform growth stocks during any given period. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer’s bonds generally take precedence over the claims of those who own preferred stock or common stock.
Loomis Sayles Small Cap Value Fund | Foreign Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Foreign Securities Risk is the risk that the value of the Fund’s foreign investments will fall as a result of foreign political, social, economic, environmental, credit, informational or currency changes or other issues relating to foreign investing generally. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity. The Fund’s investments in foreign securities may be subject to foreign withholding or other taxes, which would decrease the yield on those securities.
Loomis Sayles Small Cap Value Fund | Leverage Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Leverage Risk is the risk associated with securities or investment practices (e.g., borrowing and the use of certain derivatives) that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments (such as futures and forward currency contracts) may involve leverage. When a derivative is used as a hedge against an offsetting position that the Fund also holds, any gains generated by the derivative should be substantially offset by losses on the hedged instrument, and vice versa. To the extent that the Fund uses a derivative for purposes other than as a hedge, or if the Fund hedges imperfectly, the Fund is directly exposed to the risks of that derivative and any loss generated by the derivative will not be offset by a gain. The use of leverage increases the impact of gains and losses on the Fund’s returns, and may lead to significant losses if investments are not successful.
Loomis Sayles Small Cap Value Fund | Liquidity Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Liquidity Risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund’s investments when it needs to dispose of them. Markets may become illiquid quickly. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. During times of market turmoil, there may be no buyers or sellers for securities in certain asset classes and dealers may be unwilling or unable to make a market for certain securities. Securities acquired in a private placement, such as Rule 144A securities and privately negotiated equity and other investments, are generally subject to significant liquidity risk because they are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. In other circumstances, liquid investments may become illiquid. Derivatives, and particularly over-the-counter (“OTC”) derivatives, are generally subject to liquidity risk as well. Liquidity issues may also make it difficult to value the Fund’s investments. The Fund may invest in liquid investments that become illiquid due to financial distress, or geopolitical events such as sanctions, trading halts or wars.
Loomis Sayles Small Cap Value Fund | Management Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.
Loomis Sayles Small Cap Value Fund | REITs Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
REITs Risk is the risk that the value of the Fund’s investments in REITs will fall as a result of changes in underlying real estate values, rising interest rates, limited diversification of holdings, higher costs and prepayment risk associated with related mortgages, as well as other risks particular to investments in real estate. Many REITs are highly leveraged, increasing their risk. The Fund will indirectly bear its proportionate share of expenses, including management fees, paid by each REIT in which it invests in addition to the expenses of the Fund.
Loomis Sayles Small Cap Value Fund | Small Capitalization Companies Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Small-Capitalization Companies Risk is the risk that the Fund’s investments may be subject to more abrupt price movements, limited markets, increased volatility and less liquidity than investments in larger, more established companies, which could adversely affect the value of the portfolio.
Loomis Sayles Small Cap Value Fund | Investments in Other Investment Companies Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Investments in Other Investment Companies Risk is the risk that the Fund will indirectly bear the management service and other fees of the other investment company in addition to its own expenses.
Loomis Sayles Small Cap Value Fund | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.96%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.06% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.90%
1 year rr_ExpenseExampleYear01 $ 92
3 years rr_ExpenseExampleYear03 300
5 years rr_ExpenseExampleYear05 525
10 years rr_ExpenseExampleYear10 $ 1,173
2015 rr_AnnualReturn2015 (3.36%)
2016 rr_AnnualReturn2016 26.47%
2017 rr_AnnualReturn2017 10.02%
2018 rr_AnnualReturn2018 (16.52%)
2019 rr_AnnualReturn2019 25.08%
2020 rr_AnnualReturn2020 2.18%
2021 rr_AnnualReturn2021 29.01%
2022 rr_AnnualReturn2022 (11.54%)
2023 rr_AnnualReturn2023 19.45%
2024 rr_AnnualReturn2024 10.95%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 27.47%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (33.76%)
Past 1 Year rr_AverageAnnualReturnYear01 10.95%
Past 5 Years rr_AverageAnnualReturnYear05 9.10%
Past 10 Years rr_AverageAnnualReturnYear10 8.06%
Loomis Sayles Small Cap Value Fund | Retail Class  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 1.21%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.06% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.15%
1 year rr_ExpenseExampleYear01 $ 117
3 years rr_ExpenseExampleYear03 378
5 years rr_ExpenseExampleYear05 659
10 years rr_ExpenseExampleYear10 $ 1,461
Past 1 Year rr_AverageAnnualReturnYear01 10.69%
Past 5 Years rr_AverageAnnualReturnYear05 8.83%
Past 10 Years rr_AverageAnnualReturnYear10 7.79%
Loomis Sayles Small Cap Value Fund | Admin Class  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.47% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 1.47%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.40%
1 year rr_ExpenseExampleYear01 $ 143
3 years rr_ExpenseExampleYear03 458
5 years rr_ExpenseExampleYear05 796
10 years rr_ExpenseExampleYear10 $ 1,751
Past 1 Year rr_AverageAnnualReturnYear01 10.42%
Past 5 Years rr_AverageAnnualReturnYear05 8.55%
Past 10 Years rr_AverageAnnualReturnYear10 7.52%
Loomis Sayles Small Cap Value Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.13%
Total annual fund operating expenses rr_ExpensesOverAssets 0.88%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.85%
1 year rr_ExpenseExampleYear01 $ 87
3 years rr_ExpenseExampleYear03 278
5 years rr_ExpenseExampleYear05 485
10 years rr_ExpenseExampleYear10 $ 1,082
Past 1 Year rr_AverageAnnualReturnYear01 11.00%
Past 5 Years rr_AverageAnnualReturnYear05 9.14%
Past 10 Years rr_AverageAnnualReturnYear10 8.12%
Loomis Sayles Small Cap Value Fund | Return After Taxes on Distributions | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 8.38%
Past 5 Years rr_AverageAnnualReturnYear05 5.90%
Past 10 Years rr_AverageAnnualReturnYear10 5.13%
Loomis Sayles Small Cap Value Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 8.30%
Past 5 Years rr_AverageAnnualReturnYear05 6.81%
Past 10 Years rr_AverageAnnualReturnYear10 5.88%
Loomis Sayles Small Cap Value Fund | Russell 3000® Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 23.81%
Past 5 Years rr_AverageAnnualReturnYear05 13.86%
Past 10 Years rr_AverageAnnualReturnYear10 12.55%
Loomis Sayles Small Cap Value Fund | Russell 2000® Value Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 8.05%
Past 5 Years rr_AverageAnnualReturnYear05 7.29%
Past 10 Years rr_AverageAnnualReturnYear10 7.14%
Loomis Sayles Small Cap Value Fund | Russell 2000® Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 11.54%
Past 5 Years rr_AverageAnnualReturnYear05 7.40%
Past 10 Years rr_AverageAnnualReturnYear10 7.82%
[1] Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.90%, 1.15%, 1.40% and 0.85% of the Fund’s average daily net assets for Institutional Class shares, Retail Class shares, Admin Class shares and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2026 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class-by-class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation at the time such amounts were waived/reimbursed and (2) the class’ current applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed. 
[2] Natixis Advisors, LLC (“Natixis Advisors”) has given a binding contractual undertaking to the Fund to reimburse any and all transfer agency expenses for Class N shares. This undertaking is in effect through January 31, 2026 and may be terminated before then only with the consent of the Fund’s Board of Trustees.
[3] Other expenses include an administrative services fee of 0.25% for Admin Class shares.