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Label Element Value
(Loomis Sayles Intermediate Duration Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

Investment Goal

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is above-average total return through a combination of current income and capital appreciation.
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 and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in the Natixis Fund 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 69 of the Prospectus, in Appendix A to the Prospectus and on page 115 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").
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 Fund Complex.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
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, 2019
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other expenses are estimated for the current fiscal year.
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 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, except that the example is 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 dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. 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:
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 216% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 216.00%
Strategy [Heading] rr_StrategyHeading

Investments, Risks and Performance

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). It is anticipated that the Fund's weighted average duration will generally be between two and five years. Duration is a measure of the expected life of a fixed-income security that is used to determine the sensitivity of a security's price to changes in interest rates. A fund with a longer average portfolio duration will be more sensitive to changes in interest rates than a fund with a shorter average portfolio duration. By way of example, the price of a bond fund with an average duration of five years would be expected to fall approximately 5% if interest rates rose by one percentage point.

The Fund will purchase only investment-grade fixed-income securities, which are those securities that are rated in one of the top four rating categories at the time of purchase by at least one of the three major ratings agencies (Moody's Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) or, if unrated, are determined by Loomis Sayles to be of comparable quality. The Fund may continue to hold up to 10% of its net assets in securities that are downgraded to a rating below investment-grade subsequent to their purchase if Loomis Sayles believes it is appropriate to do so.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, for example, including, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields ("spreads") of various fixed-income securities in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

The Fund may invest up to 20% of its assets in U.S. dollar-denominated foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain 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 the issuer is included in the U.S. fixed-income indices published by Bloomberg Barclays. The Fund may also invest in mortgage-related securities, including mortgage dollar rolls. The Fund may also engage in futures transactions for hedging and investment purposes.

The fixed-income securities in which the Fund may invest include, among other things, corporate bond and other debt securities (including junior and senior bonds), U.S. government securities, zero-coupon securities, mortgage-backed securities and other asset-backed securities, real estate investment trusts ("REITs") and securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities").

The Fund may also engage in active and frequent trading of securities. Frequent trading may produce a high level of taxable gains, including short-term capital gains taxable as ordinary income, as well as increased trading costs, which may lower the Fund's return.
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.

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.

Credit/Counterparty Risk: Credit/counterparty risk is the risk that the issuer or guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

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 securities or other instruments 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.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures 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 involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for 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 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.

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 the U.S. government 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.

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.

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 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Large Investor Risk: Ownership of shares of the Fund may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, including short-term capital gains taxable as ordinary income, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund's expenses.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

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 the 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. 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.

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.

REITs Risk: Investments in the real estate industry, including REITs, are particularly sensitive to economic downturns and are sensitive to factors such as changes in real estate values, property taxes and tax laws, interest rates, cash flow of underlying real estate assets, occupancy rates, government regulations affecting zoning, land use and rents and the management skill and creditworthiness of the issuer. Companies in the real estate industry also may be subject to liabilities under environmental and hazardous waste laws. In addition, the value of a REIT is affected by changes in the value of the properties owned by the REIT or mortgage loans held by the REIT. REITs are also subject to default and prepayment risk. 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.
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 and ten-year periods 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.
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 2009, 7.49%

Lowest Quarterly Return: Third Quarter 2008, -2.93%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Effective August 31, 2016, the Fund's Retail Class shares and Institutional Class shares were redesignated as Class A shares and Class Y shares respectively. Accordingly, the returns shown in the table for Class A shares prior to August 31, 2016 are those of Retail Class shares, restated to reflect the sales loads of Class A shares, and the returns in the table for Class Y shares prior to August 31, 2016 are those of Institutional Class shares. Prior to the inception of Retail Class shares (May 28, 2010), performance is that of Institutional Class shares, restated to reflect the higher net expenses and sales loads of Class A shares. Prior to the inception of Class C shares (August 31, 2016), performance is that of Retail Class shares, restated to reflect the higher net expenses and sales loads of Class C shares. The Fund revised its investment strategies on May 28, 2010; performance may have been different had the current investment strategies been in place for all periods shown.

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.
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 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.
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 and ten-year periods compare to those of a broad measure of market performance.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the other classes of the Fund will vary.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress im.natixis.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-225-5478
(Loomis Sayles Intermediate Duration Bond Fund) | Bloomberg Barclays U.S. Intermediate Government/Credit Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 2.14%
Past 5 Years rr_AverageAnnualReturnYear05 1.50%
Past 10 Years rr_AverageAnnualReturnYear10 3.32%
(Loomis Sayles Intermediate Duration Bond Fund) | Class A  
Prospectus: rr_ProspectusTable  
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 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.22%
Total annual fund operating expenses rr_ExpensesOverAssets 0.72%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 489
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 639
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 802
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,275
Past 1 Year rr_AverageAnnualReturnYear01 (2.03%)
Past 5 Years rr_AverageAnnualReturnYear05 0.79%
Past 10 Years rr_AverageAnnualReturnYear10 3.64%
(Loomis Sayles Intermediate Duration Bond Fund) | Class C  
Prospectus: rr_ProspectusTable  
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 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 1.48%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.08% [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 243
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 460
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 800
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,762
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 143
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 460
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 800
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,762
Past 1 Year rr_AverageAnnualReturnYear01 0.63%
Past 5 Years rr_AverageAnnualReturnYear05 0.88%
Past 10 Years rr_AverageAnnualReturnYear10 3.19%
(Loomis Sayles Intermediate Duration Bond Fund) | Class T  
Prospectus: rr_ProspectusTable  
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 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.22% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.72%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 315
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 468
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 634
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,116
Past 1 Year rr_AverageAnnualReturnYear01 (0.25%)
Past 5 Years rr_AverageAnnualReturnYear05 1.16%
Past 10 Years rr_AverageAnnualReturnYear10 3.83%
(Loomis Sayles Intermediate Duration Bond Fund) | Class Y  
Prospectus: rr_ProspectusTable  
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 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.22%
Total annual fund operating expenses rr_ExpensesOverAssets 0.47%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 41
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 144
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 256
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 585
Annual Return 2008 rr_AnnualReturn2008 (2.53%)
Annual Return 2009 rr_AnnualReturn2009 19.12%
Annual Return 2010 rr_AnnualReturn2010 7.66%
Annual Return 2011 rr_AnnualReturn2011 5.44%
Annual Return 2012 rr_AnnualReturn2012 5.62%
Annual Return 2013 rr_AnnualReturn2013 (0.34%)
Annual Return 2014 rr_AnnualReturn2014 3.87%
Annual Return 2015 rr_AnnualReturn2015 0.76%
Annual Return 2016 rr_AnnualReturn2016 2.74%
Annual Return 2017 rr_AnnualReturn2017 2.66%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 7.49%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.49%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Third Quarter 2008, -2.93%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.93%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Past 1 Year rr_AverageAnnualReturnYear01 2.66%
Past 5 Years rr_AverageAnnualReturnYear05 1.93%
Past 10 Years rr_AverageAnnualReturnYear10 4.35%
(Loomis Sayles Intermediate Duration Bond Fund) | Class Y | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 1.67%
Past 5 Years rr_AverageAnnualReturnYear05 0.77%
Past 10 Years rr_AverageAnnualReturnYear10 2.98%
(Loomis Sayles Intermediate Duration Bond Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 1.50%
Past 5 Years rr_AverageAnnualReturnYear05 0.95%
Past 10 Years rr_AverageAnnualReturnYear10 2.84%
(Loomis Sayles Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high total investment return through a combination of current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 9% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 9.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). The Fund will normally invest at least 55% of its net assets in investment-grade fixed-income securities. The Fund may also invest up to 35% of its assets in below investment-grade fixed-income securities (commonly known as "junk bonds") and up to 20% of its assets in equity securities, such as common stocks and preferred stocks (with up to 10% of its assets in common stocks). 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., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, including, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields ("spreads") of various fixed-income securities (U.S. government securities, investment-grade corporate securities, securitized assets, high-yield corporate securities, emerging market securities, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

In deciding which equity securities to buy and sell, Loomis Sayles intends to emphasize dividend-paying stocks issued by companies with strong fundamentals and relatively limited anticipated volatility to supplement its fixed-income holdings. These securities will be selected with the same bottom-up investment process that is the foundation of the Fund's overall strategy.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other foreign securities, including emerging markets securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain 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 the issuer is included in the U.S. fixed-income indices published by Bloomberg Barclays.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities, U.S. government securities, commercial paper, zero-coupon securities, mortgage-related securities (including senior and junior loans, mortgage dollar rolls, stripped mortgage-related securities and collateralized mortgage obligations) and other asset-backed securities, when-issued securities, real estate investment trusts ("REITs"), securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), structured notes, repurchase agreements and convertible securities. The Fund may engage in options and futures transactions, foreign currency transactions (such as forward currency contracts) and swap transactions (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security).
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as forward currency contracts, structured notes, options and futures transactions and swap 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 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. This risk is greater for forward currency contracts, swaps and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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.

Inflation/Deflation 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.

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 securities and securities with longer maturities are generally 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).

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.
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 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, ten-year and life-of-class periods 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2009, 17.21%

Lowest Quarterly Return: Third Quarter 2008, -13.00%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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.
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 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.
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, ten-year and life-of-class periods compare to those of a broad measure of market performance.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the other classes of the Fund will vary.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Bond Fund) | Bloomberg Barclays U.S. Government/Credit Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.00%
Past 5 Years rr_AverageAnnualReturnYear05 2.13%
Past 10 Years rr_AverageAnnualReturnYear10 4.08%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 2.36%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Bond Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.52%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.14% [4]
Total annual fund operating expenses rr_ExpensesOverAssets 0.66%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [5]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.66%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 67
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 211
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 368
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 822
Annual Return 2008 rr_AnnualReturn2008 (21.82%)
Annual Return 2009 rr_AnnualReturn2009 37.19%
Annual Return 2010 rr_AnnualReturn2010 13.58%
Annual Return 2011 rr_AnnualReturn2011 3.76%
Annual Return 2012 rr_AnnualReturn2012 15.13%
Annual Return 2013 rr_AnnualReturn2013 5.88%
Annual Return 2014 rr_AnnualReturn2014 4.76%
Annual Return 2015 rr_AnnualReturn2015 (6.86%)
Annual Return 2016 rr_AnnualReturn2016 8.63%
Annual Return 2017 rr_AnnualReturn2017 7.48%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 17.21%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.21%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Third Quarter 2008, -13.00%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.00%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Past 1 Year rr_AverageAnnualReturnYear01 7.48%
Past 5 Years rr_AverageAnnualReturnYear05 3.82%
Past 10 Years rr_AverageAnnualReturnYear10 5.79%
(Loomis Sayles Bond Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 5.36%
Past 5 Years rr_AverageAnnualReturnYear05 1.80%
Past 10 Years rr_AverageAnnualReturnYear10 3.56%
(Loomis Sayles Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.73%
Past 5 Years rr_AverageAnnualReturnYear05 2.22%
Past 10 Years rr_AverageAnnualReturnYear10 3.65%
(Loomis Sayles Bond Fund) | Retail Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.52%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.14% [4]
Total annual fund operating expenses rr_ExpensesOverAssets 0.91%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [5]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.91%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 93
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 290
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 504
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,120
Past 1 Year rr_AverageAnnualReturnYear01 7.16%
Past 5 Years rr_AverageAnnualReturnYear05 3.55%
Past 10 Years rr_AverageAnnualReturnYear10 5.49%
(Loomis Sayles Bond Fund) | Admin Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.52%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.39% [4],[6]
Total annual fund operating expenses rr_ExpensesOverAssets 1.16%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [5]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.16%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 118
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 368
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 638
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,409
Past 1 Year rr_AverageAnnualReturnYear01 6.92%
Past 5 Years rr_AverageAnnualReturnYear05 3.30%
Past 10 Years rr_AverageAnnualReturnYear10 5.22%
(Loomis Sayles Bond Fund) | Class N  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.52%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.07% [4]
Total annual fund operating expenses rr_ExpensesOverAssets 0.59%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [5]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.59%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 189
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 329
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 738
Past 1 Year rr_AverageAnnualReturnYear01 7.56%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 3.57%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Core Disciplined Alpha Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks to outperform the Bloomberg Barclays U.S. Aggregate Bond Index (the "Index") consistently over time while maintaining a risk profile similar to that of the Index.

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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same, except that the example is based on 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 Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 694% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 694.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund intends to pursue its investment goal by utilizing a fundamental research-based investment approach with a focus on relative value investing on a risk-adjusted basis. Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). The Fund will invest primarily in investment grade securities. "Investment grade" securities are those securities that are rated in one of the top four ratings categories at the time of purchase by at least one of the three major ratings agencies (Moody's Investors Service, Inc., Fitch Investors Services, Inc. or S&P Global Ratings), or, if unrated, are determined by Loomis Sayles to be of comparable quality. The Fund will generally seek to maintain an effective duration of +/- 10% relative to the Index. Duration is a measure of the expected life of a fixed-income security that is used to determine the sensitivity of a security's price to changes in interest rates. A fund with a longer average portfolio duration will be more sensitive to changes in interest rates than a fund with a shorter average portfolio duration. By way of example, the price of a bond fund with an average duration of five years would be expected to fall approximately 5% if interest rates rose by one percentage point. While the effective duration for the Index fluctuates, as of December 31, 2017, the effective duration was approximately 5.95 years. The Fund may invest in U.S. dollar-denominated foreign securities including, but not limited to, Yankee bonds and securities issued by foreign governments, their agencies, instrumentalities and sponsored entities. The Fund may also have net exposures to futures transactions (including interest rate futures and U.S. Treasury futures) of up to 20% of its net assets for hedging and investment purposes.

The portfolio manager leads a team of investment professionals with responsibility for researching, selecting, and trading securities in specific sectors including government, mortgage-backed, credit, commercial mortgage-backed and asset-backed securities. These sector specialists are responsible for working closely with Loomis Sayles' research teams to generate investment ideas and implement them. In deciding which securities to buy and sell, the team may consider factors including, but not limited to, fundamental and quantitative analysis provided by Loomis Sayles' credit research team, current market conditions and trading information and the overall risk profile of the portfolio. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on individual issuers. The portfolio management team analyzes current market conditions, trading relationships and other fundamental factors and combines this analysis with a dynamic risk framework in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to the Index. The portfolio management team will sell a security when it has reached its target level of valuation, when there has been a change in the fundamental credit quality of the security that is not reflected in its current price or when the portfolio management team is attempting to reduce the overall risk of the Fund's portfolio.

The Fund may engage in active and frequent trading of securities. Frequent trading may produce a high level of taxable gains, including short-term capital gains taxable as ordinary income, as well as increased trading costs, which may lower the Fund's return. The portfolio management team continuously rotates to the best opportunities in the Fund's allowable universe. The portfolio management team identifies relative value opportunities and seeks to sell a security when its target level of valuation is reached and the security has become fully valued.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities, U.S. government and agency securities, mortgage-related securities (including adjustable rate mortgage securities, mortgage dollar rolls and collateralized mortgage obligations) and other asset-backed securities, when-issued and "to be announced" securities, securities issued pursuant to Rule 144A under the Securities Act of 1933, as amended ("Rule 144A securities"), structured notes and convertible securities.
Risk [Heading] rr_RiskHeading

Principal 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.

Agency Securities Risk is the risk that the Fund's agency securities are subject to fixed-income 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 is the risk that the issuer or guarantor of a fixed-income security in which the Fund invests, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as futures 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 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. This risk is greater for futures and other over-the-counter 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.

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.

Inflation/Deflation 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.

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 securities with longer maturities are generally 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.

Large Investor Risk is the risk associated with ownership of shares of the Fund that may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund's expenses.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).
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 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 and life-of-fund periods compare to those of a broad measure of market performance.Updated performance information is available online at www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2017, 1.33%

Lowest Quarterly Return: Fourth Quarter 2017, 0.31%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.
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 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 and life-of-fund periods compare to those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Core Disciplined Alpha Bond Fund) | Bloomberg Barclays U.S. Aggregate Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 3.54%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 3.69%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 30, 2016
(Loomis Sayles Core Disciplined Alpha Bond Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.30%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.64%
Total annual fund operating expenses rr_ExpensesOverAssets 0.94%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.49% [7]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.45%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 251
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 472
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,110
Annual Return 2017 rr_AnnualReturn2017 3.27%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2017, 1.33%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.33%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2017
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Fourth Quarter 2017, 0.31%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.31%
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2017
Past 1 Year rr_AverageAnnualReturnYear01 3.27%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 2.92%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 30, 2016
(Loomis Sayles Core Disciplined Alpha Bond Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 1.97%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 1.69%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 30, 2016
(Loomis Sayles Core Disciplined Alpha Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 1.84%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 1.67%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 30, 2016
(Loomis Sayles Fixed Income Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high total investment return through a combination of current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 10% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities. The Fund may invest up to 35% of its assets in below investment-grade fixed-income securities (commonly known as "junk bonds") and up to 20% of its assets in equity securities, such as common stocks and preferred stocks (with up to 10% of its assets in common stocks). Below investment-grade fixed-income securities are rated below investment-grade quality (i.e., none of the three major ratings agencies (Moody's Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, including, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields ("spreads") of various fixed-income securities (U.S. government securities, investment-grade corporate securities, securitized assets, high-yield corporate securities, emerging market securities, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

In deciding which equity securities to buy and sell, Loomis Sayles intends to emphasize dividend-paying stocks issued by companies with strong fundamentals and relatively limited anticipated volatility to supplement its fixed-income holdings. These securities will be selected with the same bottom-up investment process that is the foundation of the Fund's overall strategy.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain 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 the issuer is included in the U.S. fixed-income indices published by Bloomberg Barclays.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities (including junior and senior bonds), U.S. government securities, commercial paper, zero-coupon securities, mortgage-backed securities, stripped mortgage-backed securities, collateralized mortgage obligations and other asset-backed securities, including mortgage dollar rolls, when-issued securities, real estate investment trusts ("REITs"), securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions, foreign currency transactions (such as forward currency contracts) and swap transactions (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security).
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as forward currency contracts, options and futures transactions and swap 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 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. This risk is greater for forward currency contracts, swaps and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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.

Inflation/Deflation 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.

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 securities and securities with longer maturities are generally 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).

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.
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 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 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2009, 15.08%

Lowest Quarterly Return: Third Quarter 2008, -10.46%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.
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 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.
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 measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Fixed Income Fund) | Bloomberg Barclays U.S. Government/Credit Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.00%
Past 5 Years rr_AverageAnnualReturnYear05 2.13%
Past 10 Years rr_AverageAnnualReturnYear10 4.08%
(Loomis Sayles Fixed Income Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
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 [8]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.57%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 58
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 183
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 318
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 714
Annual Return 2008 rr_AnnualReturn2008 (17.78%)
Annual Return 2009 rr_AnnualReturn2009 35.85%
Annual Return 2010 rr_AnnualReturn2010 12.90%
Annual Return 2011 rr_AnnualReturn2011 3.90%
Annual Return 2012 rr_AnnualReturn2012 15.65%
Annual Return 2013 rr_AnnualReturn2013 6.88%
Annual Return 2014 rr_AnnualReturn2014 4.62%
Annual Return 2015 rr_AnnualReturn2015 (6.03%)
Annual Return 2016 rr_AnnualReturn2016 9.94%
Annual Return 2017 rr_AnnualReturn2017 8.40%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 15.08%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.08%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Third Quarter 2008, -10.46%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (10.46%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Past 1 Year rr_AverageAnnualReturnYear01 8.40%
Past 5 Years rr_AverageAnnualReturnYear05 4.60%
Past 10 Years rr_AverageAnnualReturnYear10 6.61%
(Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 6.27%
Past 5 Years rr_AverageAnnualReturnYear05 2.29%
Past 10 Years rr_AverageAnnualReturnYear10 4.23%
(Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 5.13%
Past 5 Years rr_AverageAnnualReturnYear05 2.63%
Past 10 Years rr_AverageAnnualReturnYear10 4.22%
(Loomis Sayles Global Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high total investment return through a combination of high current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 163% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 163.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). The Fund invests primarily in investment-grade fixed-income securities worldwide, although it may invest up to 20% of its assets in below investment-grade fixed-income securities (commonly known as "junk bonds"). 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., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four rating categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. Securities held by the Fund may be denominated in any currency and may be issued by issuers located in countries with emerging securities markets. The Fund may invest in fixed-income securities of any maturity. The Fund may also invest in foreign currencies and may engage in other foreign currency transactions (such as forward currency contracts) for investment or hedging purposes.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective to identify attractive investment opportunities makes this an important component of the investment approach. Second, Loomis Sayles analyzes political, economic and other fundamental factors and combines this analysis with a comparison of the yield spreads of various fixed-income securities in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk. Third, if a security that is believed to be attractive is denominated in a foreign currency, Loomis Sayles analyzes whether to accept or to hedge the currency risk.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities, U.S. government securities, commercial paper, zero-coupon securities, securitized and mortgage-related securities (including senior and junior loans, mortgage dollar rolls and collateralized mortgage obligations) and other asset-backed securities, when-issued securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), structured notes, repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions and swap transactions (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security).
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as forward currency contracts, structured notes, options and futures transactions and swap 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 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. This risk is greater for forward currency contracts, swaps and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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.

Inflation/Deflation 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.

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 securities and securities with longer maturities are generally 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.

Large Investor Risk is the risk associated with ownership of shares of the Fund that may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund's expenses.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).
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 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, ten-year and life-of-class periods 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2009, 13.17%

Lowest Quarterly Return: Third Quarter 2008, -8.53%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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.
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 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.
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, ten-year and life-of-class periods compare to those of a broad measure of market performance.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the other classes of the Fund will vary.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Global Bond Fund) | Bloomberg Barclays Global Aggregate Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 7.39%
Past 5 Years rr_AverageAnnualReturnYear05 0.79%
Past 10 Years rr_AverageAnnualReturnYear10 3.09%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 1.02%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Global Bond Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.57% [9]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 0.80%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.08% [10]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.72%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 74
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 247
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 436
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 982
Annual Return 2008 rr_AnnualReturn2008 (8.56%)
Annual Return 2009 rr_AnnualReturn2009 22.75%
Annual Return 2010 rr_AnnualReturn2010 8.00%
Annual Return 2011 rr_AnnualReturn2011 3.78%
Annual Return 2012 rr_AnnualReturn2012 8.04%
Annual Return 2013 rr_AnnualReturn2013 (2.74%)
Annual Return 2014 rr_AnnualReturn2014 0.34%
Annual Return 2015 rr_AnnualReturn2015 (5.05%)
Annual Return 2016 rr_AnnualReturn2016 3.61%
Annual Return 2017 rr_AnnualReturn2017 8.87%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 13.17%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 13.17%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Third Quarter 2008, -8.53%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (8.53%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Past 1 Year rr_AverageAnnualReturnYear01 8.87%
Past 5 Years rr_AverageAnnualReturnYear05 0.89%
Past 10 Years rr_AverageAnnualReturnYear10 3.57%
(Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 8.78%
Past 5 Years rr_AverageAnnualReturnYear05 0.22%
Past 10 Years rr_AverageAnnualReturnYear10 2.43%
(Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 5.07%
Past 5 Years rr_AverageAnnualReturnYear05 0.41%
Past 10 Years rr_AverageAnnualReturnYear10 2.33%
(Loomis Sayles Global Bond Fund) | Retail Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.57% [9]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 1.05%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.08% [10]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.97%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 99
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 326
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 572
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,275
Past 1 Year rr_AverageAnnualReturnYear01 8.65%
Past 5 Years rr_AverageAnnualReturnYear05 0.63%
Past 10 Years rr_AverageAnnualReturnYear10 3.29%
(Loomis Sayles Global Bond Fund) | Class N  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.57% [9]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.12%
Total annual fund operating expenses rr_ExpensesOverAssets 0.69%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.02% [10]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.67%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 68
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 219
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 382
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 857
Past 1 Year rr_AverageAnnualReturnYear01 8.92%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 1.12%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Inflation Protected Securities Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high total investment return through a combination of current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same, except that the example is 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 354% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 354.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 80% of its net assets (plus any borrowings made for investment purposes) in inflation-protected securities. The emphasis will be on debt securities issued by the U.S. Treasury (Treasury Inflation-Protected Securities, or "TIPS"). The principal value of these securities is periodically adjusted according to the rate of inflation, and repayment of the original bond principal upon maturity is guaranteed by the U.S. government.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

The Fund may invest in other securities, including but not limited to inflation-protected debt securities issued by U.S. government agencies and instrumentalities other than the U.S. Treasury, by other entities such as corporations and foreign governments and by foreign issuers. The Fund may also invest in nominal (i.e., non-inflation-protected) treasury securities, corporate bonds, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), structured notes, asset-backed securities and mortgage-related securities, including mortgage dollar rolls, and may invest up to 10% of its assets in below investment-grade fixed-income securities (commonly known as "junk bonds"). 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., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity. The Fund may also invest in swaps (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security) and other derivatives. The Fund may also engage in futures transactions and foreign currency transactions (such as forward currency contracts).
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as forward currency contracts, structured notes, futures transactions and swap 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 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. This risk is greater for forward currency contracts, swaps and other over-the-counter 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.

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.

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 securities with longer maturities are generally 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).

TIPS Risk is the risk that the rate of inflation will be lower than expected. Inflation-protected securities are intended to protect against inflation by adjusting the interest or principal payable on the security by an amount based upon an index intended to measure the rate of inflation. There can be no assurance that the relevant index will accurately measure the rate of inflation, in which case the securities may not work as intended.
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 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, ten-year and life-of-class periods 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Third Quarter 2011, 4.58%

Lowest Quarterly Return: Second Quarter 2013, -6.88%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Prior to the inception of Retail Class shares (May 28, 2010), performance is that of Institutional Class shares, restated to reflect the higher net expenses of Retail Class 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 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.
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 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.
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, ten-year and life-of-class periods compare to those of a broad measure of market performance.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the other classes of the Fund will vary.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Inflation Protected Securities Fund) | Bloomberg Barclays U.S. Treasury Inflation Protected Securities Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 3.01%
Past 5 Years rr_AverageAnnualReturnYear05 0.13%
Past 10 Years rr_AverageAnnualReturnYear10 3.53%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 2.24%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2017
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.56%
Total annual fund operating expenses rr_ExpensesOverAssets 0.81%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.41% [11],[12]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 41
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 409
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 964
Annual Return 2008 rr_AnnualReturn2008 (4.41%)
Annual Return 2009 rr_AnnualReturn2009 12.33%
Annual Return 2010 rr_AnnualReturn2010 6.95%
Annual Return 2011 rr_AnnualReturn2011 12.88%
Annual Return 2012 rr_AnnualReturn2012 6.98%
Annual Return 2013 rr_AnnualReturn2013 (8.20%)
Annual Return 2014 rr_AnnualReturn2014 1.75%
Annual Return 2015 rr_AnnualReturn2015 (1.50%)
Annual Return 2016 rr_AnnualReturn2016 4.38%
Annual Return 2017 rr_AnnualReturn2017 3.61%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Third Quarter 2011, 4.58%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.58%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Second Quarter 2013, -6.88%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.88%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Past 1 Year rr_AverageAnnualReturnYear01 3.61%
Past 5 Years rr_AverageAnnualReturnYear05 (0.10%)
Past 10 Years rr_AverageAnnualReturnYear10 3.27%
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 2.54%
Past 5 Years rr_AverageAnnualReturnYear05 (0.82%)
Past 10 Years rr_AverageAnnualReturnYear10 2.10%
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 2.03%
Past 5 Years rr_AverageAnnualReturnYear05 (0.40%)
Past 10 Years rr_AverageAnnualReturnYear10 2.15%
(Loomis Sayles Inflation Protected Securities Fund) | Retail Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.56%
Total annual fund operating expenses rr_ExpensesOverAssets 1.06%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.41% [11],[12]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 296
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 545
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,257
Past 1 Year rr_AverageAnnualReturnYear01 3.34%
Past 5 Years rr_AverageAnnualReturnYear05 (0.37%)
Past 10 Years rr_AverageAnnualReturnYear10 2.99%
(Loomis Sayles Inflation Protected Securities Fund) | Class N  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.52%
Total annual fund operating expenses rr_ExpensesOverAssets 0.77%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.42% [11],[12]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.35%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 36
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 204
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 386
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 915
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 2.97%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2017
(Loomis Sayles Institutional High Income Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high total investment return through a combination of current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 17% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 17.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund will invest primarily in below investment-grade fixed-income securities (commonly known as "junk bonds") and other securities that are expected to produce a relatively high level of income (including income-producing preferred stocks and common stocks). Below investment-grade fixed-income securities are rated below investment-grade quality (i.e., none of the three major ratings agencies (Moody's Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, including, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields ("spreads") of various fixed-income securities (U.S. governments, investment-grade corporates, securitized assets, high-yield corporates, emerging markets, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

The Fund may invest any portion of its assets in Canadian securities and up to 50% of its assets in other foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain 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 the issuer is included in the U.S. fixed-income indices published by Bloomberg Barclays.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities (including junior and senior loans), U.S. government securities, commercial paper, zero-coupon securities, mortgage-backed securities, including mortgage dollar rolls, stripped mortgage-backed securities, collateralized mortgage obligations, asset-backed securities, when-issued securities, real estate investment trusts ("REITs"), securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions, foreign currency transactions (such as forward currency contracts) and swap transactions (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security).
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as forward currency contracts, options and futures transactions and swap 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 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. This risk is greater for forward currency contracts, swaps and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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.

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 securities and securities with longer maturities are generally 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).

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.
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 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 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2009, 20.00%

Lowest Quarterly Return: Fourth Quarter 2008, -16.57%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.
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 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.
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 measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Institutional High Income Fund) | Bloomberg Barclays U.S. Corporate High-Yield Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 7.50%
Past 5 Years rr_AverageAnnualReturnYear05 5.78%
Past 10 Years rr_AverageAnnualReturnYear10 8.03%
(Loomis Sayles Institutional High Income Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
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 [13]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 69
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 379
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 847
Annual Return 2008 rr_AnnualReturn2008 (25.56%)
Annual Return 2009 rr_AnnualReturn2009 54.42%
Annual Return 2010 rr_AnnualReturn2010 13.60%
Annual Return 2011 rr_AnnualReturn2011 (0.08%)
Annual Return 2012 rr_AnnualReturn2012 17.98%
Annual Return 2013 rr_AnnualReturn2013 15.07%
Annual Return 2014 rr_AnnualReturn2014 5.17%
Annual Return 2015 rr_AnnualReturn2015 (10.27%)
Annual Return 2016 rr_AnnualReturn2016 18.95%
Annual Return 2017 rr_AnnualReturn2017 8.40%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 20.00%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 20.00%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Fourth Quarter 2008, -16.57%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (16.57%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Past 1 Year rr_AverageAnnualReturnYear01 8.40%
Past 5 Years rr_AverageAnnualReturnYear05 6.96%
Past 10 Years rr_AverageAnnualReturnYear10 7.98%
(Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 5.87%
Past 5 Years rr_AverageAnnualReturnYear05 3.64%
Past 10 Years rr_AverageAnnualReturnYear10 4.73%
(Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.87%
Past 5 Years rr_AverageAnnualReturnYear05 4.07%
Past 10 Years rr_AverageAnnualReturnYear10 4.93%
(Loomis Sayles Investment Grade Fixed Income Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is above-average total investment return through a combination of current income and capital appreciation.
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 3% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 3.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in investment-grade fixed-income securities. The Fund may invest up to 10% of its assets in below investment-grade fixed-income securities ("junk bonds") and up to 10% of its assets in equity securities (including preferred stocks and common stocks). Below investment-grade fixed-income securities are rated below investment-grade quality (i.e., none of the three major ratings agencies (Moody's Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund's fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity.

In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, including, for example, the stability and volatility of a country's bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio's risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).

Three themes typically drive the Fund's investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles' credit research team's assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields ("spreads") of various fixed-income securities (U.S. governments, investment-grade corporates, securitized assets, high-yield corporates, emerging markets, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

In deciding which equity securities to buy and sell, Loomis Sayles intends to emphasize dividend-paying stocks issued by companies with strong fundamentals and relatively limited anticipated volatility to supplement its fixed-income holdings. These securities will be selected with the same bottom-up investment process that is the foundation of the Fund's overall strategy.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other foreign securities, including emerging market securities and may invest, without limit, in obligations of supranational entities (e.g., the World Bank). Although certain 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 the issuer is included in the U.S. fixed-income indices published by Bloomberg Barclays. The Fund may also invest in mortgage-related securities, including mortgage dollar rolls. The Fund may engage in futures transactions and swaps (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security).

The fixed-income securities in which the Fund may invest include, among other instruments, corporate securities, U.S. government securities, zero-coupon securities, mortgage-backed securities, collateralized mortgage obligations, when-issued securities, REITs, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities") and structured notes, among others.
Risk [Heading] rr_RiskHeading

Principal 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.

Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund's investments in below investment-grade fixed-income securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as structured notes, futures transactions and swap 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 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. This risk is greater for swaps and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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.

Inflation/Deflation 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.

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 securities and securities with longer maturities are generally 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.

Large Investor Risk is the risk associated with ownership of shares of the Fund that may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund's expenses.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund's investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks).

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.
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 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 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Second Quarter 2009, 11.36%

Lowest Quarterly Return: Third Quarter 2008, -7.61%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.
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 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.
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 measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Investment Grade Fixed Income Fund) | Bloomberg Barclays U.S. Government/Credit Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.00%
Past 5 Years rr_AverageAnnualReturnYear05 2.13%
Past 10 Years rr_AverageAnnualReturnYear10 4.08%
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.40%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.09%
Total annual fund operating expenses rr_ExpensesOverAssets 0.49%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [14]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 157
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 274
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 616
Annual Return 2008 rr_AnnualReturn2008 (11.32%)
Annual Return 2009 rr_AnnualReturn2009 26.38%
Annual Return 2010 rr_AnnualReturn2010 12.90%
Annual Return 2011 rr_AnnualReturn2011 5.24%
Annual Return 2012 rr_AnnualReturn2012 12.89%
Annual Return 2013 rr_AnnualReturn2013 1.46%
Annual Return 2014 rr_AnnualReturn2014 4.28%
Annual Return 2015 rr_AnnualReturn2015 (4.27%)
Annual Return 2016 rr_AnnualReturn2016 6.41%
Annual Return 2017 rr_AnnualReturn2017 8.42%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 11.36%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 11.36%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Third Quarter 2008, -7.61%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (7.61%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Past 1 Year rr_AverageAnnualReturnYear01 8.42%
Past 5 Years rr_AverageAnnualReturnYear05 3.16%
Past 10 Years rr_AverageAnnualReturnYear10 5.79%
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 6.61%
Past 5 Years rr_AverageAnnualReturnYear05 1.41%
Past 10 Years rr_AverageAnnualReturnYear10 3.63%
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.92%
Past 5 Years rr_AverageAnnualReturnYear05 1.73%
Past 10 Years rr_AverageAnnualReturnYear10 3.71%
(Loomis Sayles Small Cap Value Fund)  
Prospectus: rr_ProspectusTable  
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 and hold shares of the Fund.

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, 2019
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 the Fund's operating expenses remain the same, except that the examples for the Institutional Class, Retail Class and Admin Class shares are based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement for the first year and on the Total Annual Fund Operating Expenses for the remaining years. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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%
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. Loomis Sayles will consider, among other things, price-to-earnings, price-to-book and price-to-cash flow ratios. The Fund's investments may include companies that have suffered significant business problems but are believed by Loomis Sayles to have favorable prospects for recovery and 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, 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

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

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 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. This risk is greater for forward currency contracts and other over-the-counter 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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 present the risk that their lower valuations fairly reflect their business prospects or that other 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.

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.

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.

Large Investor Risk is the risk associated with ownership of shares of the Fund that may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund's expenses.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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 is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.

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.

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.

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.
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 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, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Russell 2000® Value Index is an unmanaged index that measures the performance of those Russell 2000® companies with lower price-to-book ratios and lower forecasted growth values. The Russell 2000® Index is an unmanaged index that consists of the 2,000 smallest companies in the Russell 3000® Index. This index shows how the Fund's returns compare to a commonly-used broad based index focused on small-cap securities. 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 .
Bar Chart [Heading] rr_BarChartHeading

Total Returns for Institutional Class Shares

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: Third Quarter 2009, 19.42%

Lowest Quarterly Return: Fourth Quarter 2008, -23.69%

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2017)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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.
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 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.
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, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the other classes of the Fund will vary.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Small Cap Value Fund) | Russell 2000® Value Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 7.84%
Past 5 Years rr_AverageAnnualReturnYear05 13.01%
Past 10 Years rr_AverageAnnualReturnYear10 8.17%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 11.71%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Small Cap Value Fund) | Russell 2000® Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 14.65%
Past 5 Years rr_AverageAnnualReturnYear05 14.12%
Past 10 Years rr_AverageAnnualReturnYear10 8.71%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 12.77%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
(Loomis Sayles Small Cap Value Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.18%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05% [15]
Total annual fund operating expenses rr_ExpensesOverAssets 0.98%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [16]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 309
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 539
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,199
Annual Return 2008 rr_AnnualReturn2008 (31.81%)
Annual Return 2009 rr_AnnualReturn2009 28.84%
Annual Return 2010 rr_AnnualReturn2010 25.07%
Annual Return 2011 rr_AnnualReturn2011 (1.57%)
Annual Return 2012 rr_AnnualReturn2012 16.34%
Annual Return 2013 rr_AnnualReturn2013 35.94%
Annual Return 2014 rr_AnnualReturn2014 5.33%
Annual Return 2015 rr_AnnualReturn2015 (3.36%)
Annual Return 2016 rr_AnnualReturn2016 26.47%
Annual Return 2017 rr_AnnualReturn2017 10.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Third Quarter 2009, 19.42%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 19.42%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Fourth Quarter 2008, -23.69%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (23.69%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Past 1 Year rr_AverageAnnualReturnYear01 10.02%
Past 5 Years rr_AverageAnnualReturnYear05 14.00%
Past 10 Years rr_AverageAnnualReturnYear10 9.25%
(Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 7.11%
Past 5 Years rr_AverageAnnualReturnYear05 11.29%
Past 10 Years rr_AverageAnnualReturnYear10 7.90%
(Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 8.09%
Past 5 Years rr_AverageAnnualReturnYear05 10.85%
Past 10 Years rr_AverageAnnualReturnYear10 7.41%
(Loomis Sayles Small Cap Value Fund) | Retail Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.18%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05% [15]
Total annual fund operating expenses rr_ExpensesOverAssets 1.23%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [16]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.20%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 122
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 387
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 673
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,486
Past 1 Year rr_AverageAnnualReturnYear01 9.78%
Past 5 Years rr_AverageAnnualReturnYear05 13.72%
Past 10 Years rr_AverageAnnualReturnYear10 8.98%
(Loomis Sayles Small Cap Value Fund) | Admin Class  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.43% [17]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05% [15]
Total annual fund operating expenses rr_ExpensesOverAssets 1.48%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [16]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.45%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 148
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 465
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 805
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,766
Past 1 Year rr_AverageAnnualReturnYear01 9.50%
Past 5 Years rr_AverageAnnualReturnYear05 13.44%
Past 10 Years rr_AverageAnnualReturnYear10 8.71%
(Loomis Sayles Small Cap Value Fund) | Class N  
Prospectus: rr_ProspectusTable  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.08%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05% [15]
Total annual fund operating expenses rr_ExpensesOverAssets 0.88%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [16]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.88%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 90
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 281
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 488
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,084
Past 1 Year rr_AverageAnnualReturnYear01 10.13%
Life of Fund / Life of Class N rr_AverageAnnualReturnSinceInception 12.85%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
[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 0.65%, 1.40%, 0.65% and 0.40% of the Fund's average daily net assets for Class A, C, 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, 2019 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, 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 are estimated for the current fiscal year.
[4] The expense information shown in the table above includes acquired fund fees and expenses of less than 0.01%.
[5] 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 0.70%, 0.95%, 1.20% and 0.65% 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, 2019 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 Institutional Class shares, Retail Class shares, Admin Class shares and Class N 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.
[6] Other expenses include an administrative services fee of 0.25% for Admin Class shares.
[7] 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 0.45% of the Fund's average daily net assets for Institutional Class shares, 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, 2019 and may be terminated before then only with the consent of the Fund's Board of Trustees. The Adviser will be permitted to recover management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below the expense limitation for Institutional Class 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.
[8] 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 0.65% of the Fund's average daily net assets, 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, 2019 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. 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.
[9] Management fees have been restated to reflect current management fees for the fund effective July 1, 2017.
[10] 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 0.72%, 0.97% and 0.67% of the Fund's average daily net assets for Institutional Class shares, Retail 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, 2019 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 Institutional Class shares, Retail Class shares and Class N 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.
[11] 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 0.40%, 0.65% and 0.35% of the Fund's average daily net assets for Institutional Class shares, Retail 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, 2019 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 Institutional Class shares, Retail Class shares and Class N 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.
[12] Natixis Advisors, L.P. ("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, 2019 and may be terminated before then only with the consent of the Fund's Board of Trustees.
[13] 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 0.75% of the Fund's average daily net assets, 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, 2019 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. 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.
[14] 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 0.55% of the Fund's average daily net assets, 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, 2019 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. 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.
[15] The expense information shown in the table above differs from the expense information disclosed in the Fund's financial highlights table because the financial highlights table reflects the operating expenses of the Fund and does not include acquired fund fees and expenses.
[16] 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, 2019 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 Institutional Class shares, Retail Class shares, Admin Class shares and Class N 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.
[17] Other expenses include an administrative services fee of 0.25% for Admin Class shares.