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Loomis Sayles Growth Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund’s investment goal is long-term growth of capital.
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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Funds Complex.
More information about these and other discounts is
available from your financial professional and in the section “How Sales Charges Are Calculated” on page
62 of the Prospectus
, in Appendix A to the
Prospectus and on page 
120 in the section “Reduced Sales Charges” of the Statement of Additional Information (“SAI”).
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 January 31, 2022
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
19% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 19.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock
A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the
date of purchase.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Funds Complex.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other expenses for Class T shares are estimated for the current fiscal year.
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 (except where indicated). 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 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:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If shares are not redeemed:
Strategy [Heading] rr_StrategyHeading Investments, Risks and Performance Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the Fund will invest primarily in equity securities, including common stocks, convertible securities and warrants. The Fund
focuses on stocks of large capitalization companies, but the Fund may invest in companies of any size.
The Fund normally invests across a wide range of sectors and industries. The Fund’s portfolio manager employs a growth style of equity management, which
means that the Fund seeks to invest in companies with sustainable competitive advantages versus others, long-term structural growth drivers that will lead to
above-average future cash flow growth, attractive cash flow returns on invested capital, and management teams focused on creating long-term value for
shareholders. The Fund’s portfolio manager also aims to invest in companies when they trade at a significant discount to the estimate of intrinsic value (i.e.,
companies with share prices trading significantly below what the portfolio manager believes the share price should be).
The Fund will consider selling a portfolio investment when the portfolio manager believes an unfavorable structural change occurs within a given business or
the markets in which it operates, a critical underlying investment assumption is flawed, when a more attractive reward-to-risk opportunity becomes available,
when the current price fully reflects intrinsic value, or for other investment reasons which the portfolio manager deems appropriate.
The Fund may also invest up to 20% of its assets in foreign securities, including depositary receipts and emerging market 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 or if the security’s country of
risk defined by Bloomberg is the United States. The Fund may also engage in foreign currency transactions (including foreign currency forwards and foreign
currency futures) for hedging purposes, invest in options for hedging and investment purposes and invest in securities issued pursuant to Rule 144A under the
Securities Act of 1933 (“Rule 144A securities”). Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its
assets that it may invest in these instruments.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money
by investing in the Fund. 
 
The significance of any specific risk to an investment in the Fund will vary over time, depending on the composition of the Fund’s portfolio, market conditions,
and other factors. You should read all of the risk information presented below carefully, because any one or more of these risks may result in losses to the
Fund.
Equity Securities Risk:
The value of the Fund’s investments in equity securities could be subject to unpredictable declines in the value of individual
securities and periods of below-average performance in individual securities or in the equity market as a whole. Growth stocks are generally more sensitive
to market movements than other types of stocks primarily because their stock prices are based heavily on future expectations. If the Adviser’s assessment of
the prospects for a company’s growth is wrong, or if the Adviser’s judgment of how other investors will value the company’s growth is wrong, then the price
of the company’s stock may fall or not approach the value that the Adviser has placed on it. 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. 
Market/Issuer Risk:
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. 
Management Risk:
A strategy used by the Fund’s 
portfolio manager may fail to produce the intended result.
 
Liquidity Risk:
  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. Decreases in the number of financial institutions willing to make markets in the Fund’s investments or in their capacity or willingness to transact may
increase the Fund’s exposure to this risk. 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. 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. Securities acquired in a private
placement, such as Rule 144A securities, 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.
Derivatives, and particularly OTC derivatives, are generally subject to liquidity risk
as well. Liquidity issues may also make it difficult to value the Fund’s investments.
Foreign Securities Risk:
Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty
and information
risks. The Fund’s investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities
may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.
Emerging Markets Risk:
In addition to the risks of investing in foreign investments generally, emerging markets investments are subject to greater risks
arising from political or economic instability, nationalization or confiscatory taxation, currency exchange restrictions, sanctions by other countries (such as the
United States) and an issuer’s unwillingness or inability to make principal or interest payments on its obligations. Emerging markets companies may be
smaller and have shorter operating histories than companies in developed markets.
Small- and Mid-Capitalization Companies Risk:
Compared to large-capitalization companies, small- and mid-capitalization companies are more likely to
have limited product lines, markets or financial resources. Stocks of these companies often trade less frequently and in limited volume and their prices may
fluctuate more than stocks of large-capitalization companies. As a result, it may be relatively more difficult for the Fund to buy and sell securities of small-
and mid-capitalization companies.
Credit/Counterparty Risk:
Credit/counterparty risk is the risk that the issuer or guarantor of a fixed-income security, 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. The Fund will be subject to credit/counterparty risks with respect to the counterparties to
its derivatives transactions. This risk will be heightened to the extent the Fund enters into derivative transactions with a single counterparty (or affiliated
counterparties that are part of the same organization), causing the Fund to have significant exposure to such counterparty. Many of the protections afforded
to participants on organized exchanges and clearing houses, such as the performance guarantee given by a central clearing house, are not available in
connection with over-the-counter (“OTC”) derivatives transactions, such as foreign currency transactions. For centrally cleared
derivatives
, such as cleared
swaps, futures and many options, the primary credit/counterparty risk is the creditworthiness of the Fund’s clearing broker and the central clearing house
itself. 
Currency Risk:
Fluctuations in the exchange rates between different currencies may negatively affect an investment.
The Fund may be subject to currency
risk because it may invest in currency related instruments and may invest in securities or other instruments denominated in, or that generate income
denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur
losses that would not have been incurred had the risk been hedged.
Cybersecurity and Technology Risk:
The Fund, its service providers, and other market participants increasingly depend on complex information
technology and communications systems, which 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.
Derivatives Risk:
Derivative instruments (such as those in which the Fund may invest, including foreign currency forwards, foreign currency futures and
options) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of
derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have
a significant impact on the Fund’s exposure to securities markets values, interest rates or currency exchange rates. It is possible that the Fund’s liquid assets
may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a
speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those
that would have occurred had derivatives not been used. The Fund’s use of derivatives involves other risks, such as
foreign currency forwards, foreign
currency futures and options, involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for forward
currency contracts and other OTC derivatives),the credit risk relating to the other party to a derivative contract (which is greater for forward currency
contracts, uncleared swaps and other OTC derivatives), the risk of difficulties in pricing and valuation, the risk that changes in the value of a derivative may
not correlate as expected with changes in the value of relevant assets, rates or indices; liquidity risk; allocation risk and the risk of losing more than the initial
margin (if any) required to initiate derivatives positions. 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.
Leverage Risk:
Leverage is the risk associated with securities or investment practices (e.g., borrowing and use of certain derivatives) that multiply small
index, market or asset-price movements into larger changes in value. 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.
Risk Lose Money [Text] rr_RiskLoseMoney You may lose money by investing in the Fund. 
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Risk/Return Bar Chart and Table
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The bar chart and table shown below provide some 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, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.
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 im.natixis.com and/or by calling the Fund toll-free at 800-225-5478.
The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your
return.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table shown below provide some 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, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-225-5478
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress im.natixis.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 Class Y Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Quarterly Returns: Second Quarter 2020, 23.88%

Lowest Quarterly Return: Fourth Quarter 2018, -11.64%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Returns:
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2020)
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-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 only one class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
The Fund did not have Class T shares outstanding during the periods shown above. The returns of Class T shares would have been substantially similar to the
returns of the Fund’s other share classes because they would have been invested in the same portfolio of securities and would only differ to the extent the
other share classes did not have the same expenses. Performance of Class T shares shown above is that of Class A shares, which have the same expenses as
Class T shares, restated to reflect the different sales load applicable to Class T shares. 
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 only one 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 Growth Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 0.90%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.90%
1 year rr_ExpenseExampleYear01 $ 662
3 years rr_ExpenseExampleYear03 845
5 years rr_ExpenseExampleYear05 1,045
10 years rr_ExpenseExampleYear10 $ 1,619
Past 1 Year rr_AverageAnnualReturnYear01 23.88%
Past 5 Years rr_AverageAnnualReturnYear05 17.22%
Past 10 Years rr_AverageAnnualReturnYear10 15.79%
Loomis Sayles Growth Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 1.65%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.65%
1 year rr_ExpenseExampleYear01 $ 268
3 years rr_ExpenseExampleYear03 520
5 years rr_ExpenseExampleYear05 897
10 years rr_ExpenseExampleYear10 1,955
1 year rr_ExpenseExampleNoRedemptionYear01 168
3 years rr_ExpenseExampleNoRedemptionYear03 520
5 years rr_ExpenseExampleNoRedemptionYear05 897
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,955
Past 1 Year rr_AverageAnnualReturnYear01 29.42%
Past 5 Years rr_AverageAnnualReturnYear05 17.72%
Past 10 Years rr_AverageAnnualReturnYear10 15.61%
Loomis Sayles Growth Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.07%
Total annual fund operating expenses rr_ExpensesOverAssets 0.57%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.57%
1 year rr_ExpenseExampleYear01 $ 58
3 years rr_ExpenseExampleYear03 183
5 years rr_ExpenseExampleYear05 318
10 years rr_ExpenseExampleYear10 $ 714
Past 1 Year rr_AverageAnnualReturnYear01 31.88%
Past 5 Years rr_AverageAnnualReturnYear05 19.03%
Past 10 Years rr_AverageAnnualReturnYear10
Since Inception rr_AverageAnnualReturnSinceInception 17.84%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Loomis Sayles Growth Fund | Class T  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.15% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.90%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.90%
1 year rr_ExpenseExampleYear01 $ 340
3 years rr_ExpenseExampleYear03 530
5 years rr_ExpenseExampleYear05 736
10 years rr_ExpenseExampleYear10 $ 1,330
Past 1 Year rr_AverageAnnualReturnYear01 28.12%
Past 5 Years rr_AverageAnnualReturnYear05 18.01%
Past 10 Years rr_AverageAnnualReturnYear10 16.19%
Loomis Sayles Growth Fund | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 0.65%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.65%
1 year rr_ExpenseExampleYear01 $ 66
3 years rr_ExpenseExampleYear03 208
5 years rr_ExpenseExampleYear05 362
10 years rr_ExpenseExampleYear10 $ 810
2011 rr_AnnualReturn2011 0.72%
2012 rr_AnnualReturn2012 18.75%
2013 rr_AnnualReturn2013 35.36%
2014 rr_AnnualReturn2014 11.27%
2015 rr_AnnualReturn2015 10.02%
2016 rr_AnnualReturn2016 5.87%
2017 rr_AnnualReturn2017 32.64%
2018 rr_AnnualReturn2018 (2.48%)
2019 rr_AnnualReturn2019 31.72%
2020 rr_AnnualReturn2020 31.77%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 23.88%
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (11.64%)
Past 1 Year rr_AverageAnnualReturnYear01 31.77%
Past 5 Years rr_AverageAnnualReturnYear05 18.90%
Past 10 Years rr_AverageAnnualReturnYear10 16.76%
Loomis Sayles Growth Fund | Return After Taxes on Distributions | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 30.44%
Past 5 Years rr_AverageAnnualReturnYear05 17.98%
Past 10 Years rr_AverageAnnualReturnYear10 16.24%
Loomis Sayles Growth Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 19.75%
Past 5 Years rr_AverageAnnualReturnYear05 15.19%
Past 10 Years rr_AverageAnnualReturnYear10 14.20%
Loomis Sayles Growth Fund | Russell 1000® Growth Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 38.49%
Past 5 Years rr_AverageAnnualReturnYear05 21.00%
Past 10 Years rr_AverageAnnualReturnYear10 17.21%
Since Inception rr_AverageAnnualReturnSinceInception 18.80%
[1] A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the date of purchase.
[2] 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 1.25%, 2.00%, 0.95%, 1.25% and 1.00% of the Fund’s average daily net assets for Class A, C, N, T and Y 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, 2022 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 the applicable expense limitations for Class A, C, N, T and Y shares. 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.
[3] Other expenses for Class T shares are estimated for the current fiscal year.