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Loomis Sayles Strategic Alpha Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Strategic Alpha Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund seeks to provide an attractive absolute total return, complemented by prudent investment management designed to manage risks and protect
investor capital. The secondary goal of the Fund is to achieve these returns with relatively low volatility.
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 $100,000 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
75 of the Prospectus
, in Appendix A to the
Prospectus
and on page 
136 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 April 30, 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
498% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 498.00%
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 $100,000 in the Natixis Funds Complex.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
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 for Class C
shares for the ten-year period reflects the conversion to Class A shares after eight years. 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
The Fund has an absolute total return investment objective, which means that it is not managed relative to an index and that it attempts to achieve positive
total returns over a full market cycle. The Fund intends to pursue its objective by utilizing a flexible investment approach that allocates investments across a
global range of investment opportunities related to credit, currencies and interest rates, while employing risk management strategies to mitigate downside
risk. The Fund may invest up to 100% of its total assets in below investment grade fixed-income securities (also known as “junk bonds”) and derivatives that
have returns related to the returns on below investment grade fixed-income securities, although it is expected that, under normal market conditions, the
Fund’s net exposure (i.e., long exposures obtained through direct investments in securities and in derivatives minus short exposures obtained through
derivatives) to below investment grade fixed-income assets generally will not exceed 50% of the Fund’s total assets. Below investment-grade fixed-income
securities are rated below investment-grade quality (i.e., none of the three major rating agencies (Moody’s Investors Service, Inc. (“Moody’s”), Fitch Investor
Services, Inc. or S&P Global Ratings (“S&P”)) have rated the securities in one of their respective top four ratings categories). Under normal market conditions,
the Fund also may invest up to 50% of its total assets in investments denominated in non-U.S. currencies and related derivatives, including up to 20% in
investments denominated in emerging market currencies and related derivatives. The Fund expects that its exposure to these asset classes will often be
obtained substantially through the use of derivative instruments. The Fund defines an “emerging market currency” as a currency of a country that carries a
sovereign debt quality rating that is rated below investment grade by either S&P or Moody’s, or is unrated by both S&P and Moody’s. Currency positions that
are intended to hedge the Fund’s non-U.S. currency exposure (i.e., currency positions that are not made for investment purposes) will offset positions in the
same currency that are made for investment purposes when calculating the limitation on investments in non-U.S. and emerging market currency investments
because the Fund believes that hedging a currency position is likely to negate some or all of the currency risk associated with the original currency position.
The Fund does not have limits on the duration of its portfolio, and the Fund’s duration will change over time. The Fund also may invest in equity securities
(including preferred stocks) as well as derivatives whose returns are linked to the returns of equity securities.
In selecting investments for the Fund, the Adviser develops long-term portfolio themes driven by macro-economic indicators. These include global economic
trends, demographic trends and labor supply, analysis of global capital flows and assessments of geopolitical factors. The Adviser then develops shorter-term
portfolio strategies based on factors including, but not limited to, economic, credit and Federal Reserve cycles, and top-down sector valuations and bottom-up
security valuations. The Adviser seeks to actively manage risk, with a focus on managing the Fund’s exposure to credit, interest rate and currency risks in
relation to the market. Additionally, the portfolio managers will use risk management tools, such as models that evaluate risk correlation to various market
factors or asset classes, to seek to manage risk on an ongoing basis. The portfolio management team expects to actively evaluate each investment idea and
to decide to buy or sell an investment based upon: (i) its return potential; (ii) its level of risk; and (iii) its fit within the team’s overall macro strategy, with the
goal of continually optimizing the Fund’s portfolio. The Adviser incorporates systematic and quantitative models with respect to selection of certain
investments.
The Adviser currently targets an annualized volatility range of 4% to 6% (as measured by the standard deviation of the Fund’s returns). The Fund’s actual or
realized volatility during certain periods or over time may materially exceed or be lower than its target volatility range for various reasons, including changes
in market levels of volatility and because the Fund’s portfolio may include instruments that are inherently volatile. This would increase the risk of investing in
the Fund.
The Fund will pursue its investment goal by obtaining long investment exposures through investments in securities and derivatives and short investment
exposures substantially through derivatives. A “long” investment exposure is an investment that rises in value with a rise in the value of an asset, asset class
or index and declines in value with a decline in the value of that asset, asset class or index. A “short” investment exposure is an investment that rises in
value with a decline in the value of an asset, asset class or index and declines in value with a rise in the value of that asset, asset class or index. The value of
the Fund’s long and short investment exposures may, at times, each reach 100% of the assets invested in the Fund (excluding instruments primarily used for
duration management or yield curve management and short-term investments (such as cash and money market instruments)), although these exposures may
be higher or lower at any given time.
Fixed-Income Investments.
In connection with its principal investment strategies, the Fund may invest in a broad range of U.S. and non-U.S. fixed-income
securities, including, but not limited to, corporate bonds, municipal securities, U.S. and non-U.S. government securities (including their agencies,
instrumentalities and sponsored entities), securities of supranational entities, emerging market securities, commercial and residential mortgage-backed
securities, collateralized mortgage obligations, other mortgage-related securities (such as adjustable rate mortgage securities), asset-backed securities,
collateralized loan obligations, bank loans, convertible bonds, securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A
securities”), real estate investment trusts (“REITs”), zero-coupon securities, step coupon securities, pay-in-kind (“PIK”) securities, inflation-linked bonds,
variable and floating rate securities, private placements and commercial paper.
Non-U.S. Currency Investments.
Under normal market conditions, the Fund may engage in a broad range of transactions involving non-U.S. and emerging
market currencies, including, but not limited to, purchasing and selling forward currency exchange contracts in non-U.S. or emerging market currencies,
investing in non-U.S. currency futures contracts, investing in options on non-U.S. currencies and non-U.S. currency futures, investing in cross-currency
instruments (such as swaps), investing directly in non-U.S. currencies and investing in securities denominated in non-U.S. currencies. The Fund may engage in
non-U.S. currency transactions for investment or for hedging purposes.
Derivative Investments.
For investment and hedging purposes, the Fund may invest substantially in a broad range of derivatives instruments and
sometimes the majority of its investment returns will derive from its derivative investments. These derivative instruments include, but are not limited to,
futures contracts (such as treasury futures and index futures), forward contracts, options (such as options on futures contracts, options on securities, interest
rate/bond options, currency options, options on swaps and over-the-counter (“OTC”) options), warrants (such as non-U.S. currency warrants), swap
transactions (such as interest rate swaps, total return swaps and index swaps) and structured notes (such as equity-linked notes). In addition, the Fund may
invest in credit derivative products that may be used to manage default risk and credit exposure. Examples of such products include, but are not limited to,
credit default swap index products (such as LCDX, CMBX and ABX index products), single name credit default swaps, loan credit default swaps and asset-
backed credit default swaps. The Fund may, at times, invest substantially all of its assets in derivatives and securities used to support its obligations under
those derivatives. The Fund’s strategy may be highly dependent on the use of derivatives, and to the extent that they become unavailable or unattractive the
Fund may be unable to fully implement its investment strategy.
Equity Investments.
In connection with its principal investment strategies, the Fund may invest in common stocks, preferred stocks and convertible
preferred stocks.
The Fund is non-diversified, which means it may invest a greater portion of its assets in a particular issuer and may invest in fewer issuers. Because the Fund
may invest in the securities of fewer issuers, an investment in the Fund may involve a higher degree of risk than would be present in a diversified portfolio.
The Fund expects to engage in active and frequent trading of securities and other instruments. Effects of frequent trading may include high transaction costs,
which may lower the Fund’s return, and realization of greater short-term capital gains, distributions of which are taxable as ordinary income to taxable
shareholders. Trading costs and tax effects associated with frequent trading may adversely affect the Fund’s performance.
The percentage limitations set forth herein are not investment restrictions and the Fund may exceed these limits from time to time. In addition, when
calculating these exposures, the Fund may use the market value, the notional value, an adjusted notional value or some other measure of the value of a
derivative in order to reflect what the Adviser believes to be the most accurate assessment of the Fund’s real economic exposure. The total notional value of
the Fund’s derivative instruments may significantly exceed the total value of the Fund’s assets.
Although the Fund seeks positive total returns over time, the Fund’s investment returns may be volatile over short periods of time. The Fund may outperform
the overall securities market during periods of flat or negative performance and may underperform during periods of strong market performance. There can be
no assurance that the Fund’s returns over time or during any period will be positive.
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.
Mortgage-Related and Asset-Backed Securities Risk:
In addition to the risks associated with investments in fixed-income securities generally (for
example, credit, liquidity and valuation risk), mortgage-related and asset-backed securities are subject to the risks of the mortgages and assets underlying the
securities as well as prepayment risk, the risk that the securities may be prepaid and result in the reinvestment of the prepaid amounts in securities with
lower yields than the prepaid obligations. Conversely, there is a risk that a rise in interest rates will extend the life of a mortgage-related or asset-backed
security beyond the expected prepayment time, typically reducing the security’s value, which is called extension risk. The Fund also may incur a loss when
there is a prepayment of securities that were purchased at a premium. The Fund’s investments in other asset-backed securities are subject to risks similar to
those associated with mortgage-related securities, as well as additional risks associated with the nature of the assets and the servicing of those assets.
Below Investment Grade Fixed-Income Securities Risk:
The Fund’s investments in below investment grade fixed-income securities, also known as
“junk bonds,” may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk,
credit/counterparty risk (including a greater risk of default) and liquidity risk. The ability of the issuer to make principal and interest payments is predominantly
speculative for below investment grade fixed-income securities.
Interest Rate Risk:
Interest rate risk is the risk that the value of the Fund’s investments will fall if interest rates rise.
 Generally, the value of fixed-income
securities rises when prevailing interest rates fall and falls when interest rates rise.  Interest rate risk generally is greater for funds that invest in fixed-income
securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. 
The value of zero-coupon and PIK bonds
may be more sensitive to fluctuations in interest rates than other fixed-income securities. In addition, an economic downturn or period of rising interest rates
could adversely affect the market for these securities and reduce the Fund’s ability to sell them, negatively impacting the performance of the Fund. Potential
future changes in government monetary policy may affect the level of interest rates. 
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.
Agency Securities Risk:
Certain debt securities issued or guaranteed by agencies of the U.S. government are guaranteed as to the payment of principal
and interest by the relevant entity but have not been backed by the full faith and credit of the U.S. government. Instead, they have been supported only by the
discretionary authority of the U.S. government to purchase the agency’s obligations. An event affecting the guaranteeing entity could adversely affect the
payment of principal or interest or both on the security and, therefore, these types of securities should be considered to be riskier than U.S. government
securities.
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 risk with respect to the counterparties to
its derivative 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 a significant portion of its assets 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 futures contracts, forward contracts, options, warrants and
swap transactions) 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, such as
futures, forward contracts, options, warrants,
foreign currency transactions, swaps, credit default swaps and equity-linked and other structured notes, involves other risks, such as the credit risk relating to
the other party to a derivative contract (which is greater for forward 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 derivatives 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. 
There is a risk that the Adviser’s
use of derivatives, such as futures and forward contracts, to manage the Fund’s volatility may be ineffective or may exacerbate losses, for example, if the
derivative or the underlying assets decrease in value over time. When used, derivatives may affect the amount, timing or character of distributions payable to,
and thus taxes payable by, shareholders. Similarly, for accounting and performance reporting purposes, income and gain characteristics may be different than
if the Fund held the underlying securities or assets directly.
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. 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.
Inflation/Deflation Risk:
Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases
the present value of future payments. Deflation risk is the risk that prices throughout the economy decline over time (the opposite of inflation). Deflation may
have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s
portfolio. Because the Fund seeks positive returns that exceed the rate of inflation over time, if the portfolio managers’ inflation forecasts are incorrect, the
Fund may be more severely impacted than other funds.
Leverage Risk:
Taking short positions in securities results in a form of leverage. Leverage 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. 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.
LIBOR Risk:
LIBOR risk is the risk that the transition away from the London Interbank Offered Rate (“LIBOR”) may lead to increased volatility and illiquidity in
markets that are tied to LIBOR. LIBOR is a benchmark interest rate that is used extensively as a “reference rate” for financial instruments, including many
corporate and municipal bonds, bank loans, asset-backed and mortgage-related securities, interest rate swaps and other derivatives. Additionally, the Fund
may borrow money at rates that are based on LIBOR. In July 2017, the head of the United Kingdom Financial Conduct Authority (“FCA”), the agency that
oversees LIBOR, announced a desire to phase out the use of LIBOR by the end of 2021. The FCA and LIBOR’s administrator, ICE Benchmark Administration,
have announced that most LIBOR rates will no longer be published after the end of 2021 and a majority of U.S. dollar LIBOR rates will no longer be published
after June 30, 2023. The transition away from LIBOR poses a number of other risks, including changed values of LIBOR-related investments and reduced
effectiveness of hedging strategies, each of which may adversely affect the Fund’s performance.
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.
 Liquidity issues may also make it difficult to value the Fund’s investments.
Management Risk:
A strategy used by the Fund’s 
portfolio managers may fail to produce the intended result.
 
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.
The Fund’s Adviser will attempt to reduce this risk by implementing various volatility
management strategies and techniques. However, there is no guarantee that such strategies and techniques will produce the intended result.
Models and Data Risk:
The Adviser utilizes various proprietary quantitative models to identify investment opportunities. There is a possibility that one or all
of the quantitative models may fail to identify profitable opportunities at any time. Furthermore, the models may incorrectly identify opportunities and these
misidentified opportunities may lead to substantial losses for the Fund. Models may be predictive in nature and such models may result in an incorrect
assessment of future events. Data used in the construction of models may prove to be inaccurate or stale, which may result in losses for the Fund.
Non-Diversification Risk:
Compared with other mutual funds, the Fund may invest a greater percentage of its assets in a particular issuer and may invest
in fewer issuers. Therefore, the Fund may have more risk because changes in the value of a single security or the impact of a single economic, political or
regulatory occurrence may have a greater adverse impact on the Fund’s net asset value.
Short Exposure Risk:
A short exposure through a derivative may present various risks, including credit/counterparty risk and leverage risk. If the value of
the asset, asset class or index on which the Fund has obtained a short investment exposure increases, the Fund will incur a loss. Unlike a direct cash
investment such as a stock, bond or ETF, where the potential loss is limited to the purchase price, the potential risk of loss from a short exposure is
theoretically unlimited. Moreover, there can be no assurance that securities necessary to cover (repurchase in order to close) a short position will be available
for purchase.
Risk Lose Money [Text] rr_RiskLoseMoney You may lose money by investing in the Fund.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus Non-Diversification Risk: Compared with other mutual funds, the Fund may invest a greater percentage of its assets in a particular issuer and may invest in fewer issuers. Therefore, the Fund may have more risk because changes in the value of a single security or the impact of a single economic, political or regulatory occurrence may have a greater adverse impact on the Fund’s net asset value.
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
two broad measures of market performance.
The 3-Month LIBOR +300 basis points represents the average rate at which a leading bank, for a given
currency (in this case, U.S. dollars), can obtain unsecured funding, and is representative of short-term interest rates. Class C shares will automatically convert to Class A shares after eight years.
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 two broad measures 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 Return:

Second Quarter 2020,
8.07%



Lowest Quarterly Return:

First Quarter 2020,
-5.57%
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 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-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.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
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 Fund 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 Strategic Alpha Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.25%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none [1]
Redemption fees rr_RedemptionFee none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.14%
Total annual fund operating expenses rr_ExpensesOverAssets 0.99%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.99%
1 year rr_ExpenseExampleYear01 $ 522
3 years rr_ExpenseExampleYear03 727
5 years rr_ExpenseExampleYear05 949
10 years rr_ExpenseExampleYear10 $ 1,586
Past 1 Year rr_AverageAnnualReturnYear01 5.30%
Past 5 Years rr_AverageAnnualReturnYear05 3.77%
Past 10 Years rr_AverageAnnualReturnYear10 2.79%
Loomis Sayles Strategic Alpha 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_MaximumDeferredSalesChargeOverOther 1.00%
Redemption fees rr_RedemptionFee none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.14%
Total annual fund operating expenses rr_ExpensesOverAssets 1.74%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.74%
1 year rr_ExpenseExampleYear01 $ 277
3 years rr_ExpenseExampleYear03 548
5 years rr_ExpenseExampleYear05 944
10 years rr_ExpenseExampleYear10 1,853
1 year rr_ExpenseExampleNoRedemptionYear01 177
3 years rr_ExpenseExampleNoRedemptionYear03 548
5 years rr_ExpenseExampleNoRedemptionYear05 944
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,853
Past 1 Year rr_AverageAnnualReturnYear01 8.12%
Past 5 Years rr_AverageAnnualReturnYear05 3.89%
Past 10 Years rr_AverageAnnualReturnYear10 2.61%
Loomis Sayles Strategic Alpha 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_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFee none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.08%
Total annual fund operating expenses rr_ExpensesOverAssets 0.68%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.68%
1 year rr_ExpenseExampleYear01 $ 69
3 years rr_ExpenseExampleYear03 218
5 years rr_ExpenseExampleYear05 379
10 years rr_ExpenseExampleYear10 $ 847
Past 1 Year rr_AverageAnnualReturnYear01 10.36%
Life of Class N rr_AverageAnnualReturnSinceInception 4.56%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2017
Loomis Sayles Strategic Alpha 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_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFee none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.14% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.99%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.99%
1 year rr_ExpenseExampleYear01 $ 348
3 years rr_ExpenseExampleYear03 557
5 years rr_ExpenseExampleYear05 783
10 years rr_ExpenseExampleYear10 $ 1,433
Past 1 Year rr_AverageAnnualReturnYear01 7.21%
Past 5 Years rr_AverageAnnualReturnYear05 4.15%
Past 10 Years rr_AverageAnnualReturnYear10 2.97%
Loomis Sayles Strategic Alpha 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_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFee none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.14%
Total annual fund operating expenses rr_ExpensesOverAssets 0.74%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.74%
1 year rr_ExpenseExampleYear01 $ 76
3 years rr_ExpenseExampleYear03 237
5 years rr_ExpenseExampleYear05 411
10 years rr_ExpenseExampleYear10 $ 918
2011 rr_AnnualReturn2011 (3.78%)
2012 rr_AnnualReturn2012 12.57%
2013 rr_AnnualReturn2013 1.19%
2014 rr_AnnualReturn2014 2.52%
2015 rr_AnnualReturn2015 (1.43%)
2016 rr_AnnualReturn2016 6.86%
2017 rr_AnnualReturn2017 3.38%
2018 rr_AnnualReturn2018 0.53%
2019 rr_AnnualReturn2019 3.96%
2020 rr_AnnualReturn2020 10.19%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 8.07%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.57%)
Past 1 Year rr_AverageAnnualReturnYear01 10.19%
Past 5 Years rr_AverageAnnualReturnYear05 4.93%
Past 10 Years rr_AverageAnnualReturnYear10 3.49%
Loomis Sayles Strategic Alpha Fund | Return After Taxes on Distributions | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 9.12%
Past 5 Years rr_AverageAnnualReturnYear05 3.70%
Past 10 Years rr_AverageAnnualReturnYear10 2.24%
Loomis Sayles Strategic Alpha Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 6.00%
Past 5 Years rr_AverageAnnualReturnYear05 3.24%
Past 10 Years rr_AverageAnnualReturnYear10 2.14%
Loomis Sayles Strategic Alpha Fund | 3-Month LIBOR  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 0.66%
Past 5 Years rr_AverageAnnualReturnYear05 1.46%
Past 10 Years rr_AverageAnnualReturnYear10 0.89%
Life of Class N rr_AverageAnnualReturnSinceInception 1.68%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2017
Loomis Sayles Strategic Alpha Fund | 3-Month LIBOR +300 basis points  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 3.66%
Past 5 Years rr_AverageAnnualReturnYear05 4.46%
Past 10 Years rr_AverageAnnualReturnYear10 3.89%
Life of Class N rr_AverageAnnualReturnSinceInception 4.66%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2017
[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 1.00%, 1.75%, 0.70%, 1.00% and 0.75% of the Fund’s average daily net assets for Class A, Class C, Class N, Class T and Class 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 April 30, 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, Class C, Class N, Class T and Class 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 fee/expense was waived/reimbursed.
[3] Other expenses for Class T shares are estimated for the current fiscal year.