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Label Element Value
(Loomis Sayles Bond Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 for Class N shares is 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 28% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 28.00%
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 invest primarily in investment-grade fixed-income securities, although it 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 Standard & Poor's Ratings Group) 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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 markets securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank).

The fixed-income securities in which the Fund may invest include, among other things, 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 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Because Class N shares did not have one calendar year of performance as of December 31, 2013, performance shown for Class N shares is that of Institutional Class shares of the Fund. Class N shares would have had substantially similar returns because they would have been invested in the same portfolio of securities as Institutional Class shares and would only differ to the extent the classes did not have the same expenses. The Class N returns may be higher or lower than the returns of Institutional 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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 17.21%
Lowest Quarterly Return: Third Quarter 2008, -13.00%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance 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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Bond Fund) | Barclays U.S. Government/Credit Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (2.35%)
Past 5 Years rr_AverageAnnualReturnYear05 4.40%
Past 10 Years rr_AverageAnnualReturnYear10 4.52%
(Loomis Sayles Bond Fund) | Admin Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.51%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.43% [1],[2]
Total annual fund operating expenses rr_ExpensesOverAssets 1.19%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.19%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 121
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 378
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 654
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,443
Past 1 Year rr_AverageAnnualReturnYear01 5.33%
Past 5 Years rr_AverageAnnualReturnYear05 13.90%
Past 10 Years rr_AverageAnnualReturnYear10 7.42%
(Loomis Sayles Bond Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.51%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.12% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 0.63%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 64
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 202
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 351
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 786
Annual Return 2004 rr_AnnualReturn2004 11.30%
Annual Return 2005 rr_AnnualReturn2005 4.28%
Annual Return 2006 rr_AnnualReturn2006 11.29%
Annual Return 2007 rr_AnnualReturn2007 8.53%
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%
Past 1 Year rr_AverageAnnualReturnYear01 5.88%
Past 5 Years rr_AverageAnnualReturnYear05 14.53%
Past 10 Years rr_AverageAnnualReturnYear10 8.01%
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
(Loomis Sayles Bond Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 3.55%
Past 5 Years rr_AverageAnnualReturnYear05 12.11%
Past 10 Years rr_AverageAnnualReturnYear10 5.63%
(Loomis Sayles Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 3.44%
Past 5 Years rr_AverageAnnualReturnYear05 10.61%
Past 10 Years rr_AverageAnnualReturnYear10 5.34%
(Loomis Sayles Bond Fund) | Class N
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.51%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 1.63% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 2.14%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 1.49% [3]
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 526
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,012
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,354
Past 1 Year rr_AverageAnnualReturnYear01 5.88%
Past 5 Years rr_AverageAnnualReturnYear05 14.53%
Past 10 Years rr_AverageAnnualReturnYear10 8.01%
(Loomis Sayles Bond Fund) | Retail Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.51%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.16% [1]
Total annual fund operating expenses rr_ExpensesOverAssets 0.92%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.92%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 94
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 293
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 509
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,131
Past 1 Year rr_AverageAnnualReturnYear01 5.52%
Past 5 Years rr_AverageAnnualReturnYear05 14.20%
Past 10 Years rr_AverageAnnualReturnYear10 7.70%
(Loomis Sayles Global Bond Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 for the Institutional Class shares and Class N shares is based on 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 185% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 185.00%
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 Standard & Poor's Ratings Group) 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 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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 things, 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 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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.
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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Because Class N shares did not have one calendar year of performance as of December 31, 2013, performance shown for Class N shares is that of Institutional Class shares of the Fund. Class N shares would have had substantially similar returns because they would have been invested in the same portfolio of securities as Institutional Class shares and would only differ to the extent the classes did not have the same expenses. The Class N returns may be higher or lower than the returns of Institutional 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-deferred 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. The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 13.17%
Lowest Quarterly Return: Third Quarter 2008, -8.53%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund.
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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Global Bond Fund) | Barclays Global Aggregate Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (2.60%)
Past 5 Years rr_AverageAnnualReturnYear05 3.91%
Past 10 Years rr_AverageAnnualReturnYear10 4.46%
(Loomis Sayles Global Bond Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.25%
Total annual fund operating expenses rr_ExpensesOverAssets 0.78%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [4]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.75%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 77
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 246
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 430
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 963
Annual Return 2004 rr_AnnualReturn2004 9.80%
Annual Return 2005 rr_AnnualReturn2005 (4.34%)
Annual Return 2006 rr_AnnualReturn2006 8.24%
Annual Return 2007 rr_AnnualReturn2007 8.44%
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%)
Past 1 Year rr_AverageAnnualReturnYear01 (2.74%)
Past 5 Years rr_AverageAnnualReturnYear05 7.65%
Past 10 Years rr_AverageAnnualReturnYear10 5.01%
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
(Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (4.29%)
Past 5 Years rr_AverageAnnualReturnYear05 6.21%
Past 10 Years rr_AverageAnnualReturnYear10 3.47%
(Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (1.33%)
Past 5 Years rr_AverageAnnualReturnYear05 5.47%
Past 10 Years rr_AverageAnnualReturnYear10 3.33%
(Loomis Sayles Global Bond Fund) | Class N
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.30%
Total annual fund operating expenses rr_ExpensesOverAssets 0.83%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.13% [4]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.70%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 72
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 252
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 448
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,013
Past 1 Year rr_AverageAnnualReturnYear01 (2.74%)
Past 5 Years rr_AverageAnnualReturnYear05 7.65%
Past 10 Years rr_AverageAnnualReturnYear10 5.01%
(Loomis Sayles Global Bond Fund) | Retail Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.20%
Total annual fund operating expenses rr_ExpensesOverAssets 0.98%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [4]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 100
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 312
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 542
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,201
Past 1 Year rr_AverageAnnualReturnYear01 (2.99%)
Past 5 Years rr_AverageAnnualReturnYear05 7.35%
Past 10 Years rr_AverageAnnualReturnYear10 4.70%
(Loomis Sayles Inflation Protected Securities Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 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 56% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 56.00%
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 Standard & Poor's Ratings Group) 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.
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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market risk. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

Focused Investment Risk is the risk that the Fund's portfolio is not as diversified as some of the other Funds' portfolios, which means that the Fund generally invests more of its assets in a smaller number of issuers. As a result, changes in the value of a single security may have a more significant effect on the Fund's net asset value ("NAV").

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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.

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 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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. The Fund revised its investment strategies on December 15, 2004; performance may have been different had the current investment strategies been in place for all periods shown.

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-deferred 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. The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Third Quarter 2011, 4.58%
Lowest Quarterly Return: Second Quarter 2013, -6.88%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund.
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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
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) | Barclays U.S. Treasury Inflation Protected Securities Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (8.61%)
Past 5 Years rr_AverageAnnualReturnYear05 5.63%
Past 10 Years rr_AverageAnnualReturnYear10 4.85%
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.66%
Total annual fund operating expenses rr_ExpensesOverAssets 0.91%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.51% [5]
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 239
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 454
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,073
Annual Return 2004 rr_AnnualReturn2004 4.39%
Annual Return 2005 rr_AnnualReturn2005 1.99%
Annual Return 2006 rr_AnnualReturn2006 0.60%
Annual Return 2007 rr_AnnualReturn2007 10.62%
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%)
Past 1 Year rr_AverageAnnualReturnYear01 (8.20%)
Past 5 Years rr_AverageAnnualReturnYear05 5.90%
Past 10 Years rr_AverageAnnualReturnYear10 4.20%
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
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (8.97%)
Past 5 Years rr_AverageAnnualReturnYear05 4.55%
Past 10 Years rr_AverageAnnualReturnYear10 2.58%
(Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (4.61%)
Past 5 Years rr_AverageAnnualReturnYear05 4.28%
Past 10 Years rr_AverageAnnualReturnYear10 2.73%
(Loomis Sayles Inflation Protected Securities Fund) | Retail Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.73%
Total annual fund operating expenses rr_ExpensesOverAssets 1.23%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.58% [5]
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 333
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 620
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,437
Past 1 Year rr_AverageAnnualReturnYear01 (8.37%)
Past 5 Years rr_AverageAnnualReturnYear05 5.61%
Past 10 Years rr_AverageAnnualReturnYear10 3.90%
(Loomis Sayles Intermediate Duration Bond Fund)
  
Risk/Return: rr_RiskReturnAbstract  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

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.

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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 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 124% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 124.00%
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.

The Fund will purchase only investment-grade fixed-income securities, which are those securities that are rated as such 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 Standard & Poor's Ratings Group) 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, 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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, 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 U.S. dollar-denominated securities of Canadian issuers and up to 20% of its assets in other 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). The Fund may also invest in mortgage-related securities, including mortgage dollar rolls. The Fund may also 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 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").
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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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 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.

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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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. 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.

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-deferred 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. The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 7.49%
Lowest Quarterly Return: Third Quarter 2008, -2.93%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund.
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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Intermediate Duration Bond Fund) | Barclays U.S. Intermediate Government/Credit Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (0.86%)
Past 5 Years rr_AverageAnnualReturnYear05 3.96%
Past 10 Years rr_AverageAnnualReturnYear10 4.09%
(Loomis Sayles Intermediate Duration Bond Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 0.48%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.08% [5]
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 146
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 261
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 596
Annual Return 2004 rr_AnnualReturn2004 3.35%
Annual Return 2005 rr_AnnualReturn2005 1.30%
Annual Return 2006 rr_AnnualReturn2006 4.44%
Annual Return 2007 rr_AnnualReturn2007 5.71%
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%)
Past 1 Year rr_AverageAnnualReturnYear01 (0.34%)
Past 5 Years rr_AverageAnnualReturnYear05 7.32%
Past 10 Years rr_AverageAnnualReturnYear10 4.84%
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
(Loomis Sayles Intermediate Duration Bond Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (1.53%)
Past 5 Years rr_AverageAnnualReturnYear05 5.86%
Past 10 Years rr_AverageAnnualReturnYear10 3.22%
(Loomis Sayles Intermediate Duration Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (0.13%)
Past 5 Years rr_AverageAnnualReturnYear05 5.21%
Past 10 Years rr_AverageAnnualReturnYear10 3.15%
(Loomis Sayles Intermediate Duration Bond Fund) | Retail Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.29%
Total annual fund operating expenses rr_ExpensesOverAssets 0.79%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.14% [5]
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 238
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 425
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 965
Past 1 Year rr_AverageAnnualReturnYear01 (0.50%)
Past 5 Years rr_AverageAnnualReturnYear05 7.07%
Past 10 Years rr_AverageAnnualReturnYear10 4.56%
(Loomis Sayles Small Cap Value Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 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 22% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 22.00%
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 either falls within the capitalization range of the Russell 2000® Index, an index that tracks stocks of 2,000 of the smallest U.S. companies, or is $3 billion or less at the time of investment. 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. In addition to considering the research analysts' sector-specific recommendations and other factors, the portfolio managers also employ quantitative analysis to evaluate the analysts' recommendations and construct the Fund's investment portfolio. 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 securities of foreign issuers, including emerging markets securities. 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, 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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 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.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

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 and ten-year periods 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Because Class N shares did not have one calendar year of performance as of December 31, 2013, performance shown for Class N shares is that of Institutional Class shares of the Fund. Class N shares would have had substantially similar returns because they would have been invested in the same portfolio of securities as Institutional Class shares and would only differ to the extent the classes did not have the same expenses. The Class N returns may be higher or lower than the returns of Institutional 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-deferred 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 other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Third Quarter 2009, 19.42%
Lowest Quarterly Return: Fourth Quarter 2008, -23.69%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for other classes of the Fund will vary.
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 two broad measures of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
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
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 34.52%
Past 5 Years rr_AverageAnnualReturnYear05 17.64%
Past 10 Years rr_AverageAnnualReturnYear10 8.61%
(Loomis Sayles Small Cap Value Fund) | Russell 2000® Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 38.82%
Past 5 Years rr_AverageAnnualReturnYear05 20.08%
Past 10 Years rr_AverageAnnualReturnYear10 9.07%
(Loomis Sayles Small Cap Value Fund) | Admin Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.52% [2]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 1.70%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.12% [6]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.58%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 161
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 524
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 912
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,999
Past 1 Year rr_AverageAnnualReturnYear01 35.26%
Past 5 Years rr_AverageAnnualReturnYear05 19.59%
Past 10 Years rr_AverageAnnualReturnYear10 9.92%
(Loomis Sayles Small Cap Value Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.16%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 1.09%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.01% [6]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.08%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 110
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 346
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 600
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,328
Annual Return 2004 rr_AnnualReturn2004 21.83%
Annual Return 2005 rr_AnnualReturn2005 6.24%
Annual Return 2006 rr_AnnualReturn2006 18.31%
Annual Return 2007 rr_AnnualReturn2007 3.44%
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%
Past 1 Year rr_AverageAnnualReturnYear01 35.94%
Past 5 Years rr_AverageAnnualReturnYear05 20.19%
Past 10 Years rr_AverageAnnualReturnYear10 10.48%
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
(Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 33.23%
Past 5 Years rr_AverageAnnualReturnYear05 19.63%
Past 10 Years rr_AverageAnnualReturnYear10 9.38%
(Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 22.55%
Past 5 Years rr_AverageAnnualReturnYear05 16.54%
Past 10 Years rr_AverageAnnualReturnYear10 8.49%
(Loomis Sayles Small Cap Value Fund) | Class N
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 13.70%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 14.63%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 13.60% [6]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.03%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 2,861
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 5,112
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 9,096
Past 1 Year rr_AverageAnnualReturnYear01 35.94%
Past 5 Years rr_AverageAnnualReturnYear05 20.19%
Past 10 Years rr_AverageAnnualReturnYear10 10.48%
(Loomis Sayles Small Cap Value Fund) | Retail Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.22%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 1.40%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [6]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.33%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 135
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 436
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 759
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,674
Past 1 Year rr_AverageAnnualReturnYear01 35.57%
Past 5 Years rr_AverageAnnualReturnYear05 19.89%
Past 10 Years rr_AverageAnnualReturnYear10 10.20%
(Loomis Sayles Fixed Income Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 18% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 18.00%
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 Standard & Poor's Ratings Group) 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank).

The fixed-income securities in which the Fund may invest include, among other things, 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 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return:Second Quarter 2009, 15.08%
Lowest Quarterly Return: Third Quarter 2008, -10.46%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred 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, five-year and ten-year periods compare to those of a broad measure of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Fixed Income Fund) | Barclays U.S. Government/Credit Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (2.35%)
Past 5 Years rr_AverageAnnualReturnYear05 4.40%
Past 10 Years rr_AverageAnnualReturnYear10 4.52%
(Loomis Sayles Fixed Income Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
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 [7]
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 2004 rr_AnnualReturn2004 12.22%
Annual Return 2005 rr_AnnualReturn2005 4.12%
Annual Return 2006 rr_AnnualReturn2006 10.66%
Annual Return 2007 rr_AnnualReturn2007 9.16%
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%
Past 1 Year rr_AverageAnnualReturnYear01 6.88%
Past 5 Years rr_AverageAnnualReturnYear05 14.52%
Past 10 Years rr_AverageAnnualReturnYear10 8.62%
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
(Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 4.26%
Past 5 Years rr_AverageAnnualReturnYear05 12.16%
Past 10 Years rr_AverageAnnualReturnYear10 5.98%
(Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 4.19%
Past 5 Years rr_AverageAnnualReturnYear05 10.70%
Past 10 Years rr_AverageAnnualReturnYear10 5.73%
(Loomis Sayles Institutional High Income Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 28% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 28.00%
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 Standard & Poor's Ratings Group) 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, 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, 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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).

The fixed-income securities in which the Fund may invest include, among other things, 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 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 20.00%
Lowest Quarterly Return: Fourth Quarter 2008, -16.57%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred 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, five-year and ten-year periods compare to those of a broad measure of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
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) | Barclays U.S. Corporate High-Yield Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 7.44%
Past 5 Years rr_AverageAnnualReturnYear05 18.93%
Past 10 Years rr_AverageAnnualReturnYear10 8.62%
(Loomis Sayles Institutional High Income Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
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 [8]
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 2004 rr_AnnualReturn2004 14.18%
Annual Return 2005 rr_AnnualReturn2005 6.43%
Annual Return 2006 rr_AnnualReturn2006 16.33%
Annual Return 2007 rr_AnnualReturn2007 3.89%
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%
Past 1 Year rr_AverageAnnualReturnYear01 15.07%
Past 5 Years rr_AverageAnnualReturnYear05 18.93%
Past 10 Years rr_AverageAnnualReturnYear10 10.03%
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
(Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 10.75%
Past 5 Years rr_AverageAnnualReturnYear05 15.44%
Past 10 Years rr_AverageAnnualReturnYear10 6.97%
(Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 9.67%
Past 5 Years rr_AverageAnnualReturnYear05 14.00%
Past 10 Years rr_AverageAnnualReturnYear10 6.77%
(Loomis Sayles Investment Grade Fixed Income Fund)
  
Risk/Return: rr_RiskReturnAbstract  
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)

Expense Example [Heading] rr_ExpenseExampleHeading

Example

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2015-01-31
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 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

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 Standard & Poor's Ratings Group) 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 of issuers whose credit profiles it believes are improving. Loomis Sayles' credit research team provides deep fundamental and quantitative analysis as well as ratings on over 1,000 issuers worldwide. 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 securities of other foreign issuers, including emerging market securities and may invest, without limit, in obligations of supranational entities (e.g., the World Bank). 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 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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

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 risk, counterparty risk, interest rate risk and market 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 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.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 11.36%
Lowest Quarterly Return: Third Quarter 2008, -7.61%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred 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, five-year and ten-year periods compare to those of a broad measure of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
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) | Barclays U.S. Government/Credit Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (2.35%)
Past 5 Years rr_AverageAnnualReturnYear05 4.40%
Past 10 Years rr_AverageAnnualReturnYear10 4.52%
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.40%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.07%
Total annual fund operating expenses rr_ExpensesOverAssets 0.47%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [9]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.47%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 48
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 151
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 263
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 591
Annual Return 2004 rr_AnnualReturn2004 10.26%
Annual Return 2005 rr_AnnualReturn2005 1.80%
Annual Return 2006 rr_AnnualReturn2006 8.94%
Annual Return 2007 rr_AnnualReturn2007 10.39%
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%
Past 1 Year rr_AverageAnnualReturnYear01 1.46%
Past 5 Years rr_AverageAnnualReturnYear05 11.46%
Past 10 Years rr_AverageAnnualReturnYear10 7.49%
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
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (0.65%)
Past 5 Years rr_AverageAnnualReturnYear05 9.00%
Past 10 Years rr_AverageAnnualReturnYear10 4.87%
(Loomis Sayles Investment Grade Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 1.08%
Past 5 Years rr_AverageAnnualReturnYear05 8.25%
Past 10 Years rr_AverageAnnualReturnYear10 4.94%
(Loomis Sayles High Income Opportunities Fund)
  
Risk/Return: rr_RiskReturnAbstract  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is high current income. Capital appreciation is the Fund's secondary objective.
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)*

Expense Footnotes [Text Block] rr_ExpenseFootnotesTextBlock
* The table shows net fees and expenses of the Fund as 0%, reflecting the fact that the Fund does not pay any advisory, administration or distribution and service fees, and that Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has agreed to pay certain expenses of the Fund. You should be aware, however, that shares of the Fund are available only to institutional investment advisory clients of Loomis Sayles and NGAM Advisors, L.P. ("NGAM Advisors") and to participants in certain approved "wrap fee" programs sponsored by broker-dealers and investment advisers that may be affiliated or unaffiliated with the Fund, Loomis Sayles or NGAM Advisors. The institutional investment advisory clients of Loomis Sayles and NGAM Advisors pay Loomis Sayles or NGAM Advisors a fee for their investment advisory services, while participants in "wrap fee" programs pay a "wrap" fee to the program's sponsor. The "wrap fee" program sponsors in turn pay fees to NGAM Advisors. Participants in "wrap fee" programs should carefully read the wrap fee brochure provided to them by their program's sponsor. The brochure is required to include information about the fees charged by the "wrap fee" program sponsor and the fees paid by such sponsor to NGAM Advisors. Investors pay no additional fees or expenses to purchase shares of the Fund. Investors will, however, indirectly pay a proportionate share of those costs, such as brokerage commissions, taxes and extraordinary expenses that are borne by the Fund through a reduction in their net asset value. See the section "Management" in the Statutory Prospectus.
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 41% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 41.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest substantially all of its assets, and may invest up to 100% of its assets, in high income securities ("High-Income Securities"). High-Income Securities are fixed-income securities that Loomis Sayles believes have the potential to generate relatively high levels of current income. High-Income Securities are often rated below investment-grade (below investment-grade securities are sometimes referred to as "high-yield securities" or "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 Standard & Poor's Ratings Group) 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. The Fund may invest approximately 20% of its assets in investment-grade fixed-income securities. The Fund may invest a portion of its assets in senior floating-rate loans made to U.S. and foreign borrowers. A significant portion of the securities purchased by the Fund may be issued by smaller-capitalization companies. There is no minimum rating for debt in which the Fund may invest.

Under normal market conditions, the Fund may invest up to 40% of its assets in debt obligations of foreign companies, foreign governments and their subdivisions, agencies, instrumentalities and sponsored entities ("Foreign Securities"), including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). The Fund may also invest in derivatives, including 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), purchasing or selling options or futures contracts to hedge interest rate risk.

The Fund's investments may include, among other things, corporate debt securities, U.S. government obligations, U.S. dollar-denominated foreign securities, zero-coupon and pay-in-kind securities, loan assignments and participations, delayed funding loans and revolving credit facilities, commercial paper, mortgage-backed securities, collateralized mortgage obligations, mortgage dollar rolls, collateralized debt and loan obligations and other asset-backed securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), when-issued securities, municipal bonds, repurchase agreements, debt-linked and equity-linked securities, convertible securities, preferred shares and illiquid securities.

In deciding which High-Income Securities to buy and sell, Loomis Sayles will consider, among other things, the financial strength of the issuer, yield, coupon rate, current interest rates, current valuations and comparisons of the level of risk associated with particular investments with Loomis Sayles' expectations concerning the potential return of those types of investments. As part of its investment approach, Loomis Sayles generally seeks fixed-income securities of issuers whose credit profiles Loomis Sayles believes have the potential to stabilize or improve. With respect to investments in foreign securities, Loomis Sayles will consider the global economic environment, and the economic environment of the relevant country, taking into account factors such as GDP growth, inflation and other economic conditions, monetary policy, fiscal policy, leadership and social stability.

Loomis Sayles may invest significantly in securities whose price Loomis Sayles believes is more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates.
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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

Currency Risk is the risk that the value of the Fund's investments will fall as a result of changes in exchange rates.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as 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 swaps and other over-the-counter traded derivatives. Investing in derivatives gives rise to other risks, such as leverage risk, liquidity risk, credit risk, counterparty risk, interest rate risk and market 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 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 the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer's bonds generally take precedence over the claims of those who own preferred stock or common stock.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 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, pay-in-kind bonds 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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund. Senior loans typically have adjustable rates. As a result, it is expected that the values of senior loans held by the Fund will fluctuate less in response to interest rate changes than will fixed-rate debt securities; however, the interest rates paid by these loans will generally decrease if interest rates fall. Senior loans and other fixed-income securities are subject to the risk that borrowers pay off the debts sooner than expected.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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.

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 and life-of-fund 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Second Quarter 2009, 24.41%
Lowest Quarterly Return: Fourth Quarter 2008, -18.26%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred 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, five-year and life-of-fund periods compare to those of a broad measure of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles High Income Opportunities Fund) | Barclays U.S. Corporate High-Yield Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 7.44%
Past 5 Years rr_AverageAnnualReturnYear05 18.93%
Life of Fund rr_AverageAnnualReturnSinceInception 8.61%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 12, 2004
(Loomis Sayles High Income Opportunities Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.41% [10]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.24% [10]
Total annual fund operating expenses rr_ExpensesOverAssets 0.65%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.65%
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets none
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 none
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 none
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 none
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 none
Annual Return 2005 rr_AnnualReturn2005 3.06%
Annual Return 2006 rr_AnnualReturn2006 10.88%
Annual Return 2007 rr_AnnualReturn2007 2.54%
Annual Return 2008 rr_AnnualReturn2008 (28.54%)
Annual Return 2009 rr_AnnualReturn2009 60.32%
Annual Return 2010 rr_AnnualReturn2010 15.91%
Annual Return 2011 rr_AnnualReturn2011 1.53%
Annual Return 2012 rr_AnnualReturn2012 20.77%
Annual Return 2013 rr_AnnualReturn2013 8.49%
Past 1 Year rr_AverageAnnualReturnYear01 8.49%
Past 5 Years rr_AverageAnnualReturnYear05 19.84%
Life of Fund rr_AverageAnnualReturnSinceInception 9.11%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 12, 2004
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Second Quarter 2009, 24.41%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.41%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Fourth Quarter 2008, -18.26%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (18.26%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
(Loomis Sayles High Income Opportunities Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 5.52%
Past 5 Years rr_AverageAnnualReturnYear05 16.48%
Life of Fund rr_AverageAnnualReturnSinceInception 6.08%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 12, 2004
(Loomis Sayles High Income Opportunities Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 4.81%
Past 5 Years rr_AverageAnnualReturnYear05 14.57%
Life of Fund rr_AverageAnnualReturnSinceInception 5.87%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 12, 2004
(Loomis Sayles Securitized Asset Fund)
  
Risk/Return: rr_RiskReturnAbstract  
Objective [Heading] rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund's investment objective is to seek a high level of current income consistent with capital preservation.
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)*

Expense Footnotes [Text Block] rr_ExpenseFootnotesTextBlock
* The table shows net fees and expenses of the Fund as 0%, reflecting the fact that the Fund does not pay any advisory, administration or distribution and service fees, and that Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has agreed to pay certain expenses of the Fund. You should be aware, however, that shares of the Fund are available only to institutional investment advisory clients of Loomis Sayles and NGAM Advisors, L.P. ("NGAM Advisors") and to participants in certain approved "wrap fee" programs sponsored by broker-dealers and investment advisers that may be affiliated or unaffiliated with the Fund, Loomis Sayles or NGAM Advisors. The institutional investment advisory clients of Loomis Sayles and NGAM Advisors pay Loomis Sayles or NGAM Advisors a fee for their investment advisory services, while participants in "wrap fee" programs pay a "wrap" fee to the program's sponsor. The "wrap fee" program sponsors in turn pay fees to NGAM Advisors. Participants in "wrap fee" programs should carefully read the wrap fee brochure provided to them by their program's sponsor. The brochure is required to include information about the fees charged by the "wrap fee" program sponsor and the fees paid by such sponsor to NGAM Advisors. Investors pay no additional fees or expenses to purchase shares of the Fund. Investors will, however, indirectly pay a proportionate share of those costs, such as brokerage commissions, taxes and extraordinary expenses that are borne by the Fund through a reduction in their net asset value. See the section "Management" in the Statutory Prospectus.
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 244% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 244.00%
Strategy [Heading] rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in a diversified portfolio of securitized assets, such as mortgage-backed and other asset-backed securities. Although under normal circumstances the Fund's investments are expected to consist primarily of mortgage-backed and other asset-backed securities similar to those in the Barclays U.S. Securitized Bond Index (the "Index"), the Fund may invest in any type of asset-backed security. In addition to residential and commercial asset-backed securities, the Fund may invest in asset-backed securities related to automobiles, credit cards, home equity loans, manufactured housing, utilities, and other miscellaneous asset-backed securities. The Fund may only buy securities that are rated investment-grade at the time of purchase by at least one of the three major rating agencies (Moody's Investors Service, Inc., Fitch Investor Services, Inc. or Standard & Poor's Ratings Group) or, if unrated, are determined by Loomis Sayles to be of comparable quality. It is expected that a majority of the Fund's securities will be rated AAA or Aaa by at least one of the rating agencies at the time of purchase. The Fund may continue to hold securities that are downgraded in credit rating subsequent to their purchase if Loomis Sayles believes it would be advantageous to do so.

The Fund may, without limitation, seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts (including on a "to be announced" basis) or by using investment techniques such as buybacks and dollar rolls.

Loomis Sayles uses a bottom-up, fundamental research process to select individual securities for the Fund. The decision to buy or sell a particular security is largely driven by Loomis Sayles' view of the fundamentals of the issue compared to the prevailing market valuation, which may be higher (suggesting a potential sell decision) or lower (suggesting a potential buy decision). Loomis Sayles also may seek to construct a portfolio with risk characteristics similar, but not identical to, certain of the securities in the Index. Examples of typical risk characteristics that Loomis Sayles might consider include average life, credit quality, effective duration, yield curve exposure and sector exposure. The portfolio will not necessarily exhibit similarities with the Index for some or all risk characteristics. It is currently anticipated that the Fund's effective duration will be within +/- 1 year of the effective duration of the Index.

In deciding which securities to buy and sell, Loomis Sayles will consider, among other things, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles' expectations regarding future changes in interest rates and comparisons of the level of risk associated with particular investments with Loomis Sayles' expectations concerning the potential return of those investments.

The Fund's investments may also include, among other things, the following: fixed and floating-rate instruments, mortgage pass-through securities issued or guaranteed by agencies or instrumentalities of the U.S. Government, collateralized mortgage obligations, commercial mortgage-backed securities, mortgage-related asset-backed securities, other collateralized asset-backed securities, U.S. government securities, corporate debt securities, zero-coupon securities, step coupon securities, commercial paper, structured notes, other mortgage-related securities (including adjustable rate mortgage securities, stripped mortgage-backed securities and mortgage dollar rolls), when-issued securities and repurchase agreements. The Fund may also invest in options, futures 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 Fund may also engage in active and frequent trading of securities. Frequent trading may produce a high level of taxable gains, as well as increased trading costs, which may lower the Fund's return.
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 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 fail financially or otherwise be unwilling or unable to meet their obligations to the Fund.

Derivatives Risk is the risk that the value of the Fund's derivative investments such as 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 swaps and other over-the-counter traded derivatives. Investing in derivatives gives rise to other risks, such as leverage risk, liquidity risk, credit risk, counterparty risk, interest rate risk and market risk. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used.

Extension Risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the expected prepayment time, typically reducing the security's value.

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 of these securities and reduce the Fund's ability to sell them. A period of rising interest rates could negatively impact the performance of the Fund.

Issuer Risk is the risk that the value of securities may decline due to a number of reasons relating to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services.

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 loss generated by the derivative should be substantially offset by gains 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. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. 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 Risk is the risk that the market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer's financial condition, as well as overall market and economic conditions.

Mortgage-Related and Asset-Backed Securities Risk is 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 an unexpected 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. 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 market for mortgage-backed securities (and other asset-backed securities) has experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined. 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.
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 life-of-fund 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

Performance Table Heading rr_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2013)

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-deferred 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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock 
Highest Quarterly Return: Third Quarter 2009, 8.33%
Lowest Quarterly Return: Fourth Quarter 2008, -6.12%
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 Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their shares through tax-deferred 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, five-year and life-of-fund periods compare to those of a broad measure of market performance.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.com
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
(Loomis Sayles Securitized Asset Fund) | Barclays U.S. Securitized Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (1.31%)
Past 5 Years rr_AverageAnnualReturnYear05 4.39%
Life of Fund rr_AverageAnnualReturnSinceInception 4.87%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 02, 2006
(Loomis Sayles Securitized Asset Fund) | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.21% [10]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.07% [10]
Total annual fund operating expenses rr_ExpensesOverAssets 0.28%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.28%
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets none
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 none
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 none
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 none
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 none
Annual Return 2007 rr_AnnualReturn2007 5.06%
Annual Return 2008 rr_AnnualReturn2008 (7.07%)
Annual Return 2009 rr_AnnualReturn2009 24.30%
Annual Return 2010 rr_AnnualReturn2010 12.51%
Annual Return 2011 rr_AnnualReturn2011 6.72%
Annual Return 2012 rr_AnnualReturn2012 8.53%
Annual Return 2013 rr_AnnualReturn2013 0.07%
Past 1 Year rr_AverageAnnualReturnYear01 0.07%
Past 5 Years rr_AverageAnnualReturnYear05 10.14%
Life of Fund rr_AverageAnnualReturnSinceInception 6.67%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 02, 2006
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: Third Quarter 2009, 8.33%
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 8.33%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: Fourth Quarter 2008, -6.12%
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.12%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
(Loomis Sayles Securitized Asset Fund) | Institutional Class | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (2.32%)
Past 5 Years rr_AverageAnnualReturnYear05 7.85%
Life of Fund rr_AverageAnnualReturnSinceInception 4.53%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 02, 2006
(Loomis Sayles Securitized Asset Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 0.04%
Past 5 Years rr_AverageAnnualReturnYear05 7.13%
Life of Fund rr_AverageAnnualReturnSinceInception 4.39%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 02, 2006
[1] The expense information shown in the table above may differ 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.
[2] Other expenses include an administrative services fee of 0.25% for Admin Class shares.
[3] 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, 2015 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 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. 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.
[4] 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%, 1.00% and 0.70% 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, 2015 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 0.75%, 1.00% and 0.70% of the Fund's average daily net assets for Institutional Class shares, Retail Class shares and Class N shares, respectively. 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.
[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 0.40% and 0.65% of the Fund's average daily net assets for Institutional Class shares and Retail Class 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, 2015 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 0.40% and 0.65% of the Fund's average daily net assets for Institutional Class shares and Retail Class shares, respectively. 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] 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, 2015 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 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. 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.
[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 0.65% 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, 2015 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 0.65% of the Fund's average daily net assets. 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 0.75% 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, 2015 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 0.75% of the Fund's average daily net assets. 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] 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, 2015 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 0.55% of the Fund's average daily net assets. 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.
[10] The amount under Management Fees reflects the approximate amount that would be required to compensate Loomis Sayles for providing investment advisory services to the Fund (not the advisory fees charged for the entire "wrap fee" program or for the investor's separate account with Loomis Sayles), and the amount under Other Expenses reflects the amount of operating expenses of the Fund which are paid for by Loomis Sayles or its affiliates. See Note (*) above.