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  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">loomis sayles high income opportunities fund</rr:RiskReturnHeading>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;/b&gt;&lt;br/&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies &lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high current income.&lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ObjectiveSecondaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;Capital appreciation is the Fund's secondary objective. &lt;/p&gt;</rr:ObjectiveSecondaryTextBlock>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;sup&gt;*&lt;/sup&gt;&lt;/p&gt;&lt;table style="margin-left: 15pt;" cellpadding="2"&gt;&lt;tr&gt;&lt;td valign="top" width="2.5%" align="left"&gt;&lt;sup&gt;*&lt;/sup&gt;&lt;/td&gt;&lt;td valign="top" width="97.5%" align="left"&gt;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 &amp;amp; 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.&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt; &lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee. &lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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: &lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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 30% of the average value of its portfolio. &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall as a result of changes in exchange rates. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; &lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Equity Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Inflation/Deflation Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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. 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Large Investor Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Small-Capitalization Companies Risk&lt;/b&gt; 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. &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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 compared 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. &lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 24.41%, (second quarter of 2009), and the Fund's worst quarter was -18.26%, (fourth quarter of 2008). &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.2441</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member">2008-12-31</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">-0.1826</rr:BarChartLowestQuarterlyReturn>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;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 compared to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_Member" unitRef="pure">0.3</rr:PortfolioTurnoverRate>
  <rr:ManagementFeesOverAssets id="Item_2" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0041</rr:ManagementFeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:OtherExpensesOverAssets id="Item_3" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0023</rr:OtherExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0064</rr:ExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0</rr:NetExpensesOverAssets>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="USD">0</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="USD">0</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="USD">0</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="USD">0</rr:ExpenseExampleYear10>
  <rr:AnnualReturn2005 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0306</rr:AnnualReturn2005>
  <rr:AnnualReturn2006 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.1088</rr:AnnualReturn2006>
  <rr:AnnualReturn2007 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0254</rr:AnnualReturn2007>
  <rr:AnnualReturn2008 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">-0.2854</rr:AnnualReturn2008>
  <rr:AnnualReturn2009 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.6032</rr:AnnualReturn2009>
  <rr:AnnualReturn2010 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.1591</rr:AnnualReturn2010>
  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0153</rr:AnnualReturn2011>
  <rr:AnnualReturn2012 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.2077</rr:AnnualReturn2012>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.2077</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.1772</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.134</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberBarclaysUsCorporateHighYieldBondIndex_Member" unitRef="pure">0.1581</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.1024</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.0699</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.0675</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberBarclaysUsCorporateHighYieldBondIndex_Member" unitRef="pure">0.1034</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">0.0918</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.0614</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006642_MemberC000018129_Member" unitRef="pure">0.0601</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberBarclaysUsCorporateHighYieldBondIndex_Member" unitRef="pure">0.0875</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member">2004-04-12</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006642_MemberC000018129_Member">2004-04-12</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006642_MemberC000018129_Member">2004-04-12</rr:AverageAnnualReturnInceptionDate>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesHighIncomeOpportunitiesFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;b&gt;INVESTMENT OBJECTIVE&lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;b&gt;FUND FEES &amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is above-average total investment return through a combination of current income and capital appreciation.&lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006642_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. &lt;br /&gt;&lt;br /&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br&gt;(expenses that you pay each year as a percentage of the value of your investment) &lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;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:&lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover&lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 19% of the average value of its portfolio. &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;/b&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies&lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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).&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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, 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).&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks&lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:FeeWaiverOrReimbursementOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006642_MemberC000018129_Member" unitRef="pure">-0.0064</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance  that the Fund's derivative counterparties will not experience similar financial difficulties, 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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; &lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Inflation/Deflation Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related Securities Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;REITs Risk&lt;/b&gt; 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.&lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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.&lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares &lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 11.98%, (second quarter of 2003), and the Fund's worst quarter was -7.61%, (third quarter of 2008). &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableClosingTextBlock>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesSecuritizedAssetFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesSecuritizedAssetFund column period compact * ~&lt;/div&gt;</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesSecuritizedAssetFund column period compact * ~&lt;/div&gt;</rr:PerformanceTableTextBlock>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.004</rr:ManagementFeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.0008</rr:OtherExpensesOverAssets>
  <rr:ManagementFeesOverAssets id="Item_4" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0.0021</rr:ManagementFeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:OtherExpensesOverAssets id="Item_5" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0.0007</rr:OtherExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0.0028</rr:ExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0</rr:NetExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.0048</rr:ExpensesOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_6" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.0048</rr:NetExpensesOverAssets>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesGlobalBondFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesGlobalBondFund column period compact * ~&lt;/div&gt;</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesGlobalBondFund column period compact * ~&lt;/div&gt;</rr:PerformanceTableTextBlock>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesBondFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesBondFund column period compact * ~&lt;/div&gt;</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesBondFund column period compact * ~&lt;/div&gt;</rr:PerformanceTableTextBlock>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesIntermediateDurationBondFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesIntermediateDurationBondFund column period compact * ~&lt;/div&gt;</rr:PerformanceTableTextBlock>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.005</rr:ManagementFeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesFixedIncomeFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesFixedIncomeFund column period compact * ~&lt;/div&gt;</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018128_Member" unitRef="pure">0.0054</rr:ManagementFeesOverAssets>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000125494_Member" unitRef="pure">0.0054</rr:ManagementFeesOverAssets>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">0.0054</rr:ManagementFeesOverAssets>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0.006</rr:ManagementFeesOverAssets>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="USD">49</rr:ExpenseExampleYear01>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018128_Member" unitRef="pure">0.0025</rr:DistributionAndService12b1FeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000125494_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="USD">154</rr:ExpenseExampleYear03>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0.0008</rr:OtherExpensesOverAssets>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="USD">269</rr:ExpenseExampleYear05>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0.0068</rr:ExpensesOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_7" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="USD">604</rr:ExpenseExampleYear10>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">0.0018</rr:OtherExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0.0068</rr:NetExpensesOverAssets>
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  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0025</rr:DistributionAndService12b1FeesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0026</rr:OtherExpensesOverAssets>
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  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0034</rr:OtherExpensesOverAssets>
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  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0482</rr:AverageAnnualReturnYear01>
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  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.004</rr:NetExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0065</rr:NetExpensesOverAssets>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.0849</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006646_MemberC000018133_Member" unitRef="pure">0.059</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006646_MemberC000018133_Member" unitRef="pure">0.0579</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0606</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006646_MemberC000018133_Member" unitRef="pure">0.0702</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006646_MemberC000018133_Member" unitRef="pure">0.0688</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006641_MemberC000018127_Member" unitRef="pure">0.0702</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0525</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member">1996-06-05</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006641_MemberC000018127_Member" unitRef="pure">0.052</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018128_Member" unitRef="pure">0.0781</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberBarclaysGlobalAggregateBondIndex_Member" unitRef="pure">0.0432</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000125494_Member" unitRef="pure">0.0804</rr:AverageAnnualReturnYear01>
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  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0051</rr:ExpensesOverAssets>
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  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006641_MemberC000018127_Member" unitRef="pure">0.0442</rr:AverageAnnualReturnYear05>
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  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.0376</rr:AnnualReturn2011>
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  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006641_MemberC000018127_Member" unitRef="pure">0.0584</rr:AverageAnnualReturnSinceInception>
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  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.1513</rr:AverageAnnualReturnYear01>
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  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0981</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018123_Member" unitRef="pure">0.1477</rr:AverageAnnualReturnYear01>
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  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0482</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.0779</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0535</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0517</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018123_Member" unitRef="pure">0.0747</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018124_Member" unitRef="pure">0.0718</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000125493_Member" unitRef="pure">0.0779</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0606</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.1018</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0776</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.074</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018124_Member" unitRef="pure">0.0957</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000125493_Member" unitRef="pure">0.1018</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0525</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018123_Member" unitRef="pure">0.0987</rr:AverageAnnualReturnYear10>
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  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006641_MemberC000018127_Member">1991-05-10</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006641_MemberC000018127_Member">1991-05-10</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018128_Member">1991-05-10</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.1033</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000125494_Member">1991-05-10</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0725</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006638_MemberC000018122_Member" unitRef="pure">0.0707</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018123_Member" unitRef="pure">0.1004</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018124_Member" unitRef="pure">0.0959</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000125493_Member" unitRef="pure">0.1033</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0683</rr:AverageAnnualReturnSinceInception>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="USD">41</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="USD">66</rr:ExpenseExampleYear01>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006638_MemberC000018122_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="USD">152</rr:ExpenseExampleYear03>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006638_MemberC000018122_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018123_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="USD">249</rr:ExpenseExampleYear03>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018124_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000125493_Member">1991-05-16</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="USD">274</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="USD">447</rr:ExpenseExampleYear05>
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  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="USD">1020</rr:ExpenseExampleYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.0974</rr:AverageAnnualReturnYear10>
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  <rr:AnnualReturn2004 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0335</rr:AnnualReturn2004>
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  <rr:AnnualReturn2008 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">-0.0253</rr:AnnualReturn2008>
  <rr:AnnualReturn2009 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.1912</rr:AnnualReturn2009>
  <rr:AnnualReturn2010 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0766</rr:AnnualReturn2010>
  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0544</rr:AnnualReturn2011>
  <rr:AnnualReturn2012 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0562</rr:AnnualReturn2012>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;sup&gt;*&lt;/sup&gt;&lt;/p&gt;&lt;table style="margin-left: 15pt;" cellpadding="2"&gt;&lt;tr&gt;&lt;td valign="top" width="2.5%" align="left"&gt;&lt;sup&gt;*&lt;/sup&gt;&lt;/td&gt;&lt;td valign="top" width="97.5%" align="left"&gt;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 &amp;amp; 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. "Wrap fee" program participants should read carefully 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.&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt; &lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee. &lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is to seek a high level of current income consistent with capital preservation.&lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">loomis sayles fixed income fund</rr:RiskReturnHeading>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0562</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0419</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0375</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0525</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberBarclaysUsIntermediateGovernmentCreditBondIndex_Member" unitRef="pure">0.0389</rr:AverageAnnualReturnYear01>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;b&gt;INVESTMENT OBJECTIVE&lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high total investment return through a combination of current income and capital appreciation.  &lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0684</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0524</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberBarclaysUsIntermediateGovernmentCreditBondIndex_Member" unitRef="pure">0.0518</rr:AverageAnnualReturnYear05>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES &lt;/b&gt;</rr:ExpenseHeading>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0658</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0493</rr:AverageAnnualReturnYear05>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt; &lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p</rr:OperatingExpensesCaption>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example &lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0571</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0401</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0389</rr:AverageAnnualReturnYear10>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;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: &lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0541</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberBarclaysUsIntermediateGovernmentCreditBondIndex_Member" unitRef="pure">0.0462</rr:AverageAnnualReturnYear10>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0579</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.038</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006645_MemberC000018132_Member" unitRef="pure">0.0374</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member" unitRef="pure">0.0545</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberBarclaysUsIntermediateGovernmentCreditBondIndex_Member" unitRef="pure">0.0554</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">0.0804</rr:AverageAnnualReturnYear01>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio. &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE &lt;p style="margin-left:1.50em"&gt;Principal Investment Strategies &lt;/p&gt;&lt;/b&gt;</rr:StrategyHeading>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member">1998-01-28</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006645_MemberC000018132_Member">1998-01-28</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006645_MemberC000018132_Member">1998-01-28</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000089753_Member">1998-01-28</rr:AverageAnnualReturnInceptionDate>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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). &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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). &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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, 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). &lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Credit Risk &lt;/b&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Currency Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may  be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Extension Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Inflation/Deflation Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Interest Rate Risk &lt;/b&gt;is the risk that the value of the Fund's investments will fall if 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Issuer Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Leverage Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Liquidity Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt; REITs Risk&lt;/b&gt; 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. &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table &lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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. &lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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 230% of the average value of its portfolio. &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt; &lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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: &lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE &lt;/b&gt;&lt;br/&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies &lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares &lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 15.08%, (second quarter of 2009), and the Fund's worst quarter was -10.46%, (third quarter of 2008). &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012 &lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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 compared 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. &lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 8.33%, (third quarter of 2009), and the Fund's worst quarter was -6.12%, (fourth quarter of 2008). &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_Member" unitRef="pure">0.19</rr:PortfolioTurnoverRate>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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 compared to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_Member" unitRef="pure">2.3</rr:PortfolioTurnoverRate>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member">2003-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_Member" unitRef="pure">0.17</rr:PortfolioTurnoverRate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">0.1198</rr:BarChartHighestQuarterlyReturn>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member" unitRef="pure">-0.0761</rr:BarChartLowestQuarterlyReturn>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0075</rr:ManagementFeesOverAssets>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0075</rr:ManagementFeesOverAssets>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0075</rr:ManagementFeesOverAssets>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0075</rr:ManagementFeesOverAssets>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1508</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall as a result of changes in exchange rates. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt;  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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Inflation/Deflation Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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. &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">-0.1046</rr:BarChartLowestQuarterlyReturn>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0025</rr:DistributionAndService12b1FeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0025</rr:DistributionAndService12b1FeesOverAssets>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">loomis sayles institutional high income fund</rr:RiskReturnHeading>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">loomis sayles global bond fund</rr:RiskReturnHeading>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high total investment return through a combination of high current income and capital appreciation.&lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:AcquiredFundFeesAndExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0008</rr:AcquiredFundFeesAndExpensesOverAssets>
  <rr:AcquiredFundFeesAndExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0008</rr:AcquiredFundFeesAndExpensesOverAssets>
  <rr:AcquiredFundFeesAndExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0008</rr:AcquiredFundFeesAndExpensesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0007</rr:OtherExpensesOverAssets>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;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. ("Moody's"), Fitch Investor Services, Inc. ("Fitch") or Standard &amp;amp; Poor's Ratings Group ("S&amp;amp;P")) 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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, 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). &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:AcquiredFundFeesAndExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0008</rr:AcquiredFundFeesAndExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0057</rr:ExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0057</rr:NetExpensesOverAssets>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">loomis sayles bond fund</rr:RiskReturnHeading>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;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:&lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high total investment return through a combination of current income and capital appreciation. &lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES &lt;/b&gt;</rr:ExpenseHeading>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0098</rr:ExpensesOverAssets>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high total investment return through a combination of current income and capital appreciation. &lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.013</rr:ExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.016</rr:ExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0091</rr:ExpensesOverAssets>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt; &lt;br&gt;(expenses that you pay each year as a percentage of the value of your investment) &lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover&lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;b&gt;FUND FEES &amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;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 20% of the average value of its portfolio. &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member">2009-09-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;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:&lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;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 102% of the average value of its portfolio.&lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">0.0833</rr:BarChartHighestQuarterlyReturn>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;/b&gt;&lt;br /&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies&lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member">2008-12-31</rr:BarChartLowestQuarterlyReturnDate>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">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 &amp;amp; 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. &lt;br /&gt;&lt;br /&gt;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). &lt;br /&gt;&lt;br /&gt;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. &lt;br /&gt;&lt;br /&gt;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. &lt;br /&gt;&lt;br /&gt;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). &lt;br /&gt;&lt;br /&gt;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, 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).</rr:StrategyNarrativeTextBlock>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">-0.0612</rr:BarChartLowestQuarterlyReturn>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks&lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="USD">714</rr:ExpenseExampleYear10>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;  &lt;b&gt;Currency Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Inflation/Deflation Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk &lt;/b&gt;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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;REITs Risk&lt;/b&gt; 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.&lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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. &lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="USD">318</rr:ExpenseExampleYear05>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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 21% of the average value of its portfolio.  &lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 17.21%, (second quarter of 2009), and the Fund's worst quarter was -13.00%, (third quarter of 2008). &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="USD">183</rr:ExpenseExampleYear03>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0015</rr:OtherExpensesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0022</rr:OtherExpensesOverAssets>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="USD">58</rr:ExpenseExampleYear01>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0052</rr:OtherExpensesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0008</rr:OtherExpensesOverAssets>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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:   &lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;&lt;/p&gt;</rr:ObjectiveHeading>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;/b&gt;&lt;br/&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies &lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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).  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; 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).  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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, 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).  &lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties,  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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; &lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;REITs Risk&lt;/b&gt; 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.  &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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.  &lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_30" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_31" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">-0.0007</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_32" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">-0.0012</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_33" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 20.00%, (second quarter of 2009), and the Fund's worst quarter was -16.57%, (fourth quarter of 2008).  &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">loomis sayles securitized asset fund</rr:RiskReturnHeading>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0098</rr:NetExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0123</rr:NetExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0091</rr:NetExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0148</rr:NetExpensesOverAssets>
  <rr:PerformanceTableClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;Total returns shown for the Fund reflect the results of the Loomis Sayles Bond Fund, a series of Loomis Sayles Funds II (the "Predecessor Fund") whose assets and liabilities were reorganized into the Fund, a series of Loomis Sayles Funds I, on September 12, 2003. Prior to the inception of Retail Class shares (December 31, 1996) and Admin Class shares (January 2, 1998) of the Predecessor Fund, performance is that of the Institutional Class shares of the Predecessor Fund, restated to reflect the higher net expenses of the Retail Class and Admin Class shares of the Predecessor Fund. Because the Fund did not have Class N shares outstanding during the periods shown, performance is that of the 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 than the returns of Institutional Class shares because Institutional Class shares are subject to higher expenses. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableClosingTextBlock>
  <rr:AnnualReturn2003 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.3015</rr:AnnualReturn2003>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE &lt;/b&gt;&lt;br/&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies &lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesInvestmentGradeFixedIncomeFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:AnnualReturn2004 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1222</rr:AnnualReturn2004>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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. &lt;br/&gt;&lt;br/&gt;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). &lt;br/&gt;&lt;br/&gt;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. &lt;br/&gt;&lt;br/&gt;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, 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).&lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:AnnualReturn2005 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0412</rr:AnnualReturn2005>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_Member" unitRef="pure">0.21</rr:PortfolioTurnoverRate>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:AnnualReturn2006 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1066</rr:AnnualReturn2006>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_Member" unitRef="pure">0.2</rr:PortfolioTurnoverRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall as a result of changes in exchange rates. The Fund may, but is not required to, hedge its exposure to foreign currencies (including "cross hedging" between two or more foreign currencies) and may invest in foreign currencies as an asset class. 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that  the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedgding. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt; &lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Inflation/Deflation Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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.&lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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.&lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:PerformanceTableOneClassOfAfterTaxShown contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">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.</rr:PerformanceTableOneClassOfAfterTaxShown>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">0.2</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member">2008-12-31</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006644_MemberC000018131_Member" unitRef="pure">-0.1657</rr:BarChartLowestQuarterlyReturn>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 13.17%, (second quarter of 2009), and the Fund's worst quarter was -8.53%, (third quarter of 2008).&lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:Component1OtherExpensesOverAssets id="Item_34" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0</rr:Component1OtherExpensesOverAssets>
  <rr:Component1OtherExpensesOverAssets id="Item_35" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0</rr:Component1OtherExpensesOverAssets>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:Component1OtherExpensesOverAssets id="Item_36" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0</rr:Component1OtherExpensesOverAssets>
  <rr:Component1OtherExpensesOverAssets id="Item_37" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0</rr:Component1OtherExpensesOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006639_MemberC000018125_Member" unitRef="pure">-0.0028</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:Component2OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0015</rr:Component2OtherExpensesOverAssets>
  <rr:Component2OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0022</rr:Component2OtherExpensesOverAssets>
  <rr:Component2OtherExpensesOverAssets id="Item_38" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0052</rr:Component2OtherExpensesOverAssets>
  <rr:Component2OtherExpensesOverAssets id="Item_39" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.0008</rr:Component2OtherExpensesOverAssets>
  <rr:AnnualReturn2007 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0916</rr:AnnualReturn2007>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="USD">100</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="USD">125</rr:ExpenseExampleYear01>
  <rr:AnnualReturn2008 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">-0.1778</rr:AnnualReturn2008>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="USD">151</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="USD">93</rr:ExpenseExampleYear01>
  <rr:AnnualReturn2009 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.3585</rr:AnnualReturn2009>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesSecuritizedAssetFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:AnnualReturn2010 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.129</rr:AnnualReturn2010>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="USD">312</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="USD">405</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="USD">493</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="USD">290</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="USD">542</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="USD">706</rr:ExpenseExampleYear05>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006646_MemberC000018133_Member">1994-07-01</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="USD">860</rr:ExpenseExampleYear05>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006646_MemberC000018133_Member">1994-07-01</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="USD">504</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="USD">1201</rr:ExpenseExampleYear10>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006646_MemberC000018133_Member">1994-07-01</rr:AverageAnnualReturnInceptionDate>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="USD">1562</rr:ExpenseExampleYear10>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="USD">1890</rr:ExpenseExampleYear10>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="USD">1120</rr:ExpenseExampleYear10>
  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.039</rr:AnnualReturn2011>
  <rr:AnnualReturn2003 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.3455</rr:AnnualReturn2003>
  <rr:AnnualReturn2004 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.2183</rr:AnnualReturn2004>
  <rr:AnnualReturn2012 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1565</rr:AnnualReturn2012>
  <rr:AnnualReturn2005 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0624</rr:AnnualReturn2005>
  <rr:AnnualReturn2006 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1831</rr:AnnualReturn2006>
  <rr:AnnualReturn2007 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.0344</rr:AnnualReturn2007>
  <rr:AnnualReturn2008 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">-0.3181</rr:AnnualReturn2008>
  <rr:AnnualReturn2009 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.2884</rr:AnnualReturn2009>
  <rr:AnnualReturn2010 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.2507</rr:AnnualReturn2010>
  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">-0.0157</rr:AnnualReturn2011>
  <rr:AnnualReturn2012 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1634</rr:AnnualReturn2012>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">0.1721</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006638_MemberC000018122_Member" unitRef="pure">-0.13</rr:BarChartLowestQuarterlyReturn>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;br/&gt;&lt;br/&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee. &lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.1615</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.1606</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.1575</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1634</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.1087</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredValueIndex_Member" unitRef="pure">0.1805</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.1634</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredIndex_Member" unitRef="pure">0.1635</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.047</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.0461</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.0403</rr:AverageAnnualReturnYear05>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">loomis sayles intermediate duration bond fund</rr:RiskReturnHeading>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.0443</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.047</rr:AverageAnnualReturnYear05>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;b&gt;INVESTMENT OBJECTIVE&lt;/b&gt;</rr:ObjectiveHeading>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0417</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredValueIndex_Member" unitRef="pure">0.0355</rr:AverageAnnualReturnYear05>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is above-average total return through a combination of current income and capital appreciation.&lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredIndex_Member" unitRef="pure">0.0356</rr:AverageAnnualReturnYear05>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES &lt;/b&gt;</rr:ExpenseHeading>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;br/&gt;&lt;br/&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1037</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.0943</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.0889</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.1009</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.0981</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.1037</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredValueIndex_Member" unitRef="pure">0.095</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredIndex_Member" unitRef="pure">0.0972</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1211</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.1016</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006647_MemberC000018134_Member" unitRef="pure">0.0982</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member" unitRef="pure">0.1211</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member" unitRef="pure">0.1157</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member" unitRef="pure">0.119</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredValueIndex_Member" unitRef="pure">0.1112</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberRussellTwentyHundredIndex_Member" unitRef="pure">0.091</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006647_MemberC000018134_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006647_MemberC000018134_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018135_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018136_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000125495_Member">1991-05-13</rr:AverageAnnualReturnInceptionDate>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_Member" unitRef="pure">1.02</rr:PortfolioTurnoverRate>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:PerformanceTableOneClassOfAfterTaxShown contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">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.</rr:PerformanceTableOneClassOfAfterTaxShown>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">0.1317</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006641_MemberC000018127_Member" unitRef="pure">-0.0853</rr:BarChartLowestQuarterlyReturn>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt; &lt;br&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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:&lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover&lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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 82% of the average value of its portfolio.&lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;p style="margin-left:1.50em"&gt;Principal Investment Strategies&lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;br/&gt;&lt;br/&gt;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 &amp;amp; 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. &lt;br/&gt;&lt;br/&gt;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). &lt;br/&gt;&lt;br/&gt;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. &lt;br/&gt;&lt;br/&gt;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, 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). &lt;br/&gt;&lt;br/&gt;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"), securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities") and convertible securities.&lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks&lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall as a result of changes in exchange rates. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Emerging Markets Risk&lt;/b&gt; is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Large Investor Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;REITs Risk&lt;/b&gt; 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. &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-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.&lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesGlobalBondFundBarChart column period compact * ~&lt;/div&gt;

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  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 7.49%, (second quarter of 2009), and the Fund's worst quarter was -2.93%, (third quarter of 2008).&lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;br/&gt;&lt;br/&gt;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.&lt;/p&gt;</rr:PerformanceTableClosingTextBlock>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesInstitutionalHighIncomeFund column period compact * ~&lt;/div&gt;

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  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesInstitutionalHighIncomeFund column period compact * ~&lt;/div&gt;

</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesInstitutionalHighIncomeFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_Member" unitRef="pure">0.82</rr:PortfolioTurnoverRate>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006644_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInstitutionalHighIncomeFund column period compact * ~&lt;/div&gt;

</rr:PerformanceTableTextBlock>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesBondFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:PerformanceTableOneClassOfAfterTaxShown contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">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.</rr:PerformanceTableOneClassOfAfterTaxShown>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member">2009-06-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">0.0749</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006645_MemberC000018132_Member" unitRef="pure">-0.0293</rr:BarChartLowestQuarterlyReturn>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesIntermediateDurationBondFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1565</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.1359</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.1029</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0482</rr:AverageAnnualReturnYear01>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.0867</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0621</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0595</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0606</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1078</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0811</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0778</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0525</rr:AverageAnnualReturnYear10>
  <rr:OtherExpensesNewFundBasedOnEstimates contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">Other expenses for Class N shares are based on estimated amounts for the current fiscal year.</rr:OtherExpensesNewFundBasedOnEstimates>
  <rr:AverageAnnualReturnSinceInception id="Item_40" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0.1024</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception id="Item_41" decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0731</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception id="Item_42" decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006640_MemberC000018126_Member" unitRef="pure">0.0711</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception id="Item_43" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberBarclaysUsGovernmentCreditBondIndex_Member" unitRef="pure">0.0671</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member">1995-01-17</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006640_MemberC000018126_Member">1995-01-17</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006640_MemberC000018126_Member">1995-01-17</rr:AverageAnnualReturnInceptionDate>
  <rr:AnnualFundOperatingExpensesTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualFundOperatingExpensesLoomisSaylesInflationProtectedSecuritiesFund column period compact * ~&lt;/div&gt;</rr:AnnualFundOperatingExpensesTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesInflationProtectedSecuritiesFund column period compact * ~&lt;/div&gt;</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesInflationProtectedSecuritiesFund column period compact * ~&lt;/div&gt;</rr:PerformanceTableTextBlock>
  <rr:ExpenseExampleWithRedemptionTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleExpenseExampleTransposedLoomisSaylesIntermediateDurationBondFund column period compact * ~&lt;/div&gt;

</rr:ExpenseExampleWithRedemptionTableTextBlock>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">loomis sayles small cap value fund</rr:RiskReturnHeading>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;b&gt;FUND FEES &amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is long-term capital growth from investments in common stocks or other equity securities. &lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;br/&gt;&lt;br/&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee.&lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example&lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover&lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 19% of the average value of its portfolio.&lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE&lt;p style="margin-left:1.50em"&gt;Principal Investment Strategies&lt;/p&gt;&lt;/b&gt;</rr:StrategyHeading>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;br/&gt;&lt;br/&gt;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.&lt;br/&gt;&lt;br/&gt;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.&lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks&lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt; 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. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Emerging Markets Risk &lt;/b&gt;is the risk that the Fund's investments may face greater foreign securities risk. Investing in companies traded in emerging securities markets, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Equity Securities Risk&lt;/b&gt; 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 by owners of the issuer's bonds generally take precedence over the claims of those who own preferred stock or common stock. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Investments in Other Investment Companies Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk &lt;/b&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk &lt;/b&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;REITs Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Small-Capitalization Companies Risk&lt;/b&gt; 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.&lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund 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.&lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 19.42%, (third quarter of 2009), and the Fund's worst quarter was -23.69%, (fourth quarter of 2008).&lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;Total returns shown for the Fund reflect the results of the Loomis Sayles Small Cap Value Fund, a series of Loomis Sayles Funds II (the "Predecessor Fund") whose assets and liabilities were reorganized into the Fund, a series of Loomis Sayles Funds I, on September 12, 2003. For periods before the inception of Retail Class shares (December 31, 1996) and Admin Class shares (January 2, 1998) of the Predecessor Fund, the performance shown for those Classes is based on the returns of the Predecessor Fund's Institutional Class shares, adjusted to reflect the net expenses paid by Retail Class and Admin Class shares of the Predecessor Fund. Because the Fund did not have Class N shares outstanding during the periods shown, performance is that of the 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 than the returns of Institutional Class shares because Institutional Class shares are subject to higher expenses. &lt;br/&gt;&lt;br/&gt;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.&lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_Member" unitRef="pure">0.19</rr:PortfolioTurnoverRate>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;p style="margin-left:1.50em"&gt;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. The example for the Institutional Class shares and Class N shares is based on Total Annual Fund Operating Expenses for all periods. The example for Retail Class shares and Admin Class 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:  &lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of two broad measures of market performance.</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member">2009-09-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0025</rr:ManagementFeesOverAssets>
  <rr:ManagementFeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0025</rr:ManagementFeesOverAssets>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">0.1942</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0</rr:DistributionAndService12b1FeesOverAssets>
  <rr:DistributionAndService12b1FeesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0025</rr:DistributionAndService12b1FeesOverAssets>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member">2008-12-31</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006647_MemberC000018134_Member" unitRef="pure">-0.2369</rr:BarChartLowestQuarterlyReturn>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.006</rr:OtherExpensesOverAssets>
  <rr:OtherExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0073</rr:OtherExpensesOverAssets>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0085</rr:ExpensesOverAssets>
  <rr:ExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0123</rr:ExpensesOverAssets>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_44" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">-0.0045</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:PerformanceTableOneClassOfAfterTaxShown contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for other classes of the Fund will vary.</rr:PerformanceTableOneClassOfAfterTaxShown>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_45" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">-0.0058</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.004</rr:NetExpensesOverAssets>
  <rr:NetExpensesOverAssets decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0065</rr:NetExpensesOverAssets>
  <rr:ObjectiveHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;b&gt;INVESTMENT OBJECTIVE &lt;/b&gt;</rr:ObjectiveHeading>
  <rr:ObjectivePrimaryTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's investment objective is high total investment return through a combination of current income and capital appreciation. &lt;/p&gt;</rr:ObjectivePrimaryTextBlock>
  <rr:ExpenseHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;b&gt;FUND FEES &amp;amp; EXPENSES&lt;/b&gt;</rr:ExpenseHeading>
  <rr:OperatingExpensesCaption contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;ANNUAL FUND OPERATING EXPENSES&lt;/b&gt;&lt;br/&gt;(expenses that you pay each year as a percentage of the value of your investment)&lt;/p&gt;</rr:OperatingExpensesCaption>
  <rr:PortfolioTurnoverHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Portfolio Turnover &lt;/b&gt;&lt;/p&gt;</rr:PortfolioTurnoverHeading>
  <rr:PortfolioTurnoverTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;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 166% of the average value of its portfolio.&lt;/p&gt;</rr:PortfolioTurnoverTextBlock>
  <rr:ExpenseExampleHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Example &lt;/b&gt;&lt;/p&gt;</rr:ExpenseExampleHeading>
  <rr:ExpenseExampleNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;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:&lt;/p&gt;</rr:ExpenseExampleNarrativeTextBlock>
  <rr:StrategyHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;b&gt;INVESTMENTS, RISKS AND PERFORMANCE &lt;/b&gt;&lt;br/&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Investment Strategies &lt;/b&gt;&lt;/p&gt;</rr:StrategyHeading>
  <rr:RiskHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Principal Risks &lt;/b&gt;&lt;/p&gt;</rr:RiskHeading>
  <rr:BarChartAndPerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Risk/Return Bar Chart and Table&lt;/b&gt;&lt;/p&gt;</rr:BarChartAndPerformanceTableHeading>
  <rr:PerformanceNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance. Return data is unavailable for the Barclays U.S. Treasury Inflation Protected Securities Index prior to March 1, 1997. The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Prior to December 15, 2004, the Fund was managed using different principal investment strategies. Updated performance information is available online at www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330.&lt;/p&gt;</rr:PerformanceNarrativeTextBlock>
  <rr:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-fund periods compare to those of a broad measure of market performance.&lt;/p&gt;</rr:PerformanceInformationIllustratesVariabilityOfReturns>
  <rr:PerformanceAvailabilityPhone contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">800-633-3330</rr:PerformanceAvailabilityPhone>
  <rr:PerformanceAvailabilityWebSiteAddress contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">www.loomissayles.com</rr:PerformanceAvailabilityWebSiteAddress>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:BarChartHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Total Returns for Institutional Class Shares&lt;/b&gt;&lt;/p&gt;</rr:BarChartHeading>
  <rr:BarChartClosingTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;The Fund's best quarter was 4.58%, (third quarter of 2011), and the Fund's worst quarter was -5.57%, (third quarter of 2008).  &lt;/p&gt;</rr:BarChartClosingTextBlock>
  <rr:PerformanceTableHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Average Annual Total Returns for the periods ended December 31, 2012&lt;/b&gt;&lt;/p&gt;</rr:PerformanceTableHeading>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformanceTableNotRelevantToTaxDeferred contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">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.</rr:PerformanceTableNotRelevantToTaxDeferred>
  <rr:PerformanceTableOneClassOfAfterTaxShown contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">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.</rr:PerformanceTableOneClassOfAfterTaxShown>
  <rr:RiskLoseMoney contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">You may lose money by investing in the Fund.</rr:RiskLoseMoney>
  <rr:PortfolioTurnoverRate decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_Member" unitRef="pure">1.66</rr:PortfolioTurnoverRate>
  <rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">January 31, 2014</rr:FeeWaiverOrReimbursementOverAssetsDateOfTermination>
  <rr:PerformanceTableUsesHighestFederalRate contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">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.</rr:PerformanceTableUsesHighestFederalRate>
  <rr:PerformancePastDoesNotIndicateFuture contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.</rr:PerformancePastDoesNotIndicateFuture>
  <rr:ExpenseNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.&lt;/p&gt; &lt;p style="margin-left:1.50em"&gt;The Fund does not impose a sales charge, a redemption fee or an exchange fee. &lt;/p&gt;</rr:ExpenseNarrativeTextBlock>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">loomis sayles inflation protected securities fund</rr:RiskReturnHeading>
  <rr:FeeWaiverOrReimbursementOverAssets id="Item_46" decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006640_MemberC000018126_Member" unitRef="pure">0</rr:FeeWaiverOrReimbursementOverAssets>
  <rr:StrategyNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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). &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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 &amp;amp; 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. &lt;/p&gt;</rr:StrategyNarrativeTextBlock>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesFixedIncomeFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:PerformanceTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006640_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAverageAnnualTotalReturnsTransposedLoomisSaylesFixedIncomeFund column period compact * ~&lt;/div&gt;

</rr:PerformanceTableTextBlock>
  <rr:RiskNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Below Investment-Grade Fixed-Income Securities Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Credit Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Currency Risk&lt;/b&gt;  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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Derivatives Risk&lt;/b&gt;  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. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, 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 for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedgding. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Extension Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Focused Investment Risk&lt;/b&gt; 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").&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Foreign Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Interest Rate Risk&lt;/b&gt; is the risk that the value of the Fund's investments will fall if 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Issuer Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Large Investor Risk&lt;/b&gt; 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Leverage Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Liquidity Risk&lt;/b&gt; 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.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Management Risk&lt;/b&gt; is the risk that Loomis Sayles' investment techniques will be unsuccessful and cause the Fund to incur losses.  &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Market Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;Mortgage-Related and Asset-Backed Securities Risk&lt;/b&gt; 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. &lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;&lt;b&gt;TIPS Risk&lt;/b&gt; 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. &lt;/p&gt;</rr:RiskNarrativeTextBlock>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="USD">41</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear01 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="USD">66</rr:ExpenseExampleYear01>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="USD">226</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear03 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="USD">333</rr:ExpenseExampleYear03>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="USD">427</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear05 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="USD">620</rr:ExpenseExampleYear05>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="USD">1007</rr:ExpenseExampleYear10>
  <rr:ExpenseExampleYear10 decimals="INF" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="USD">1437</rr:ExpenseExampleYear10>
  <rr:AnnualReturn2003 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0299</rr:AnnualReturn2003>
  <rr:AnnualReturn2004 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0439</rr:AnnualReturn2004>
  <rr:AnnualReturn2005 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0199</rr:AnnualReturn2005>
  <rr:AnnualReturn2006 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.006</rr:AnnualReturn2006>
  <rr:AnnualReturn2007 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.1062</rr:AnnualReturn2007>
  <rr:AnnualReturn2008 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">-0.0441</rr:AnnualReturn2008>
  <rr:AnnualReturn2009 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.1233</rr:AnnualReturn2009>
  <rr:AnnualReturn2010 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0695</rr:AnnualReturn2010>
  <rr:AnnualReturn2011 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.1288</rr:AnnualReturn2011>
  <rr:AnnualReturn2012 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0698</rr:AnnualReturn2012>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0698</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0471</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0523</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0668</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear01 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberBarclaysUsTreasuryInflationProtectedSecuritiesIndex_Member" unitRef="pure">0.0698</rr:AverageAnnualReturnYear01>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0676</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0511</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.049</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0645</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear05 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberBarclaysUsTreasuryInflationProtectedSecuritiesIndex_Member" unitRef="pure">0.0704</rr:AverageAnnualReturnYear05>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.054</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0363</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0361</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0508</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnYear10 decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberBarclaysUsTreasuryInflationProtectedSecuritiesIndex_Member" unitRef="pure">0.0665</rr:AverageAnnualReturnYear10>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0748</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0503</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006643_MemberC000018130_Member" unitRef="pure">0.0496</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member" unitRef="pure">0.0703</rr:AverageAnnualReturnSinceInception>
  <rr:AverageAnnualReturnSinceInception xsi:nil="true" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberBarclaysUsTreasuryInflationProtectedSecuritiesIndex_Member" unitRef="pure" />
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member">1991-05-20</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributions_MemberS000006643_MemberC000018130_Member">1991-05-20</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013AfterTaxesOnDistributionsAndSales_MemberS000006643_MemberC000018130_Member">1991-05-20</rr:AverageAnnualReturnInceptionDate>
  <rr:AverageAnnualReturnInceptionDate contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000089752_Member">1991-05-20</rr:AverageAnnualReturnInceptionDate>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006647_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesSmallCapValueFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:HighestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member">best quarter</rr:HighestQuarterlyReturnLabel>
  <rr:BarChartHighestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member">2011-09-30</rr:BarChartHighestQuarterlyReturnDate>
  <rr:BarChartHighestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">0.0458</rr:BarChartHighestQuarterlyReturn>
  <rr:LowestQuarterlyReturnLabel contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member">worst quarter</rr:LowestQuarterlyReturnLabel>
  <rr:BarChartLowestQuarterlyReturnDate contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member">2008-09-30</rr:BarChartLowestQuarterlyReturnDate>
  <rr:BarChartLowestQuarterlyReturn decimals="4" contextRef="Duration_02Feb2012_01Feb2013S000006643_MemberC000018130_Member" unitRef="pure">-0.0557</rr:BarChartLowestQuarterlyReturn>
  <rr:BarChartTableTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;div style="display:none"&gt;~ http://www.loomissayles.com/role/ScheduleAnnualTotalReturnsLoomisSaylesInflationProtectedSecuritiesFundBarChart column period compact * ~&lt;/div&gt;

</rr:BarChartTableTextBlock>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">&lt;p style="margin-left:1.50em"&gt;Total returns shown for the Fund reflect the results of the Loomis Sayles U.S. Government Securities Fund (the "Predecessor Fund") whose assets and liabilities were reorganized into the Fund on September 12, 2003. 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.&lt;/p&gt;&lt;p style="margin-left:1.50em"&gt;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.&lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:PerformanceTableNarrativeTextBlock contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">&lt;p style="margin-left:1.50em"&gt;Total returns shown for the Fund reflect the results of the Loomis Sayles Global Bond Fund, a series of Loomis Sayles Funds II (the "Predecessor Fund") whose assets and liabilities were reorganized into the Fund, a series of Loomis Sayles Funds I, on September 12, 2003. Prior to the inception of Retail Class shares (December 31, 1996) of the Predecessor Fund, performance is that of Institutional Class shares of the Predecessor Fund, restated to reflect the higher net expenses of Retail Class shares of the Predecessor Fund. Because the Fund did not have Class N shares outstanding during the periods shown, performance is that of the 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 than the returns of Institutional Class shares because Institutional Class shares are subject to higher expenses. &lt;br/&gt;&lt;br/&gt;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.&lt;/p&gt;</rr:PerformanceTableNarrativeTextBlock>
  <rr:RiskReturnHeading contextRef="Duration_02Feb2012_01Feb2013S000006646_Member">loomis sayles investment grade fixed income fund</rr:RiskReturnHeading>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006639_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006638_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006641_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006645_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <rr:IndexNoDeductionForFeesExpensesTaxes contextRef="Duration_02Feb2012_01Feb2013S000006643_Member">Index performance reflects no deduction for fees, expenses or taxes.</rr:IndexNoDeductionForFeesExpensesTaxes>
  <link:footnoteLink xlink:type="extended" xlink:role="http://www.xbrl.org/2003/role/link">
    <link:loc xlink:type="locator" xlink:href="#Item_2" xlink:label="ManagementFeesOverAssets" />
    <link:footnote xlink:type="resource" xlink:label="footnote_ManagementFeesOverAssets" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_ManagementFeesOverAssets">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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="ManagementFeesOverAssets" xlink:to="footnote_ManagementFeesOverAssets" />
    <link:loc xlink:type="locator" xlink:href="#Item_3" xlink:label="Item_3_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_3_lbl" xlink:to="footnote_ManagementFeesOverAssets" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_6" xlink:label="FeeWaiverOrReimbursementOverAssets" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets" />
    <link:loc xlink:type="locator" xlink:href="#Item_24" xlink:label="FeeWaiverOrReimbursementOverAssets_2" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_2" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_2">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_2" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_2" />
    <link:loc xlink:type="locator" xlink:href="#Item_25" xlink:label="Item_25_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_25_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_44" xlink:label="Item_44_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_44_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_45" xlink:label="Item_45_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_45_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_46" xlink:label="FeeWaiverOrReimbursementOverAssets_3" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_3" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_3">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_3" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_3" />
    <link:loc xlink:type="locator" xlink:href="#Item_12" xlink:label="OtherExpensesOverAssets" />
    <link:footnote xlink:type="resource" xlink:label="footnote_OtherExpensesOverAssets" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_OtherExpensesOverAssets">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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="OtherExpensesOverAssets" xlink:to="footnote_OtherExpensesOverAssets" />
    <link:loc xlink:type="locator" xlink:href="#Item_13" xlink:label="Item_13_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_13_lbl" xlink:to="footnote_OtherExpensesOverAssets" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_14" xlink:label="Item_14_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_14_lbl" xlink:to="footnote_OtherExpensesOverAssets" use="optional" priority="0" order="1.0" />
    <link:footnote xlink:type="resource" xlink:label="footnote_OtherExpensesOverAssets_2" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_OtherExpensesOverAssets_2">Other expenses include an administrative service fee of 0.25% for Admin Class shares.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_14_lbl" xlink:to="footnote_OtherExpensesOverAssets_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_15" xlink:label="Item_15_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_15_lbl" xlink:to="footnote_OtherExpensesOverAssets" use="optional" priority="0" order="1.0" />
    <link:footnote xlink:type="resource" xlink:label="footnote_OtherExpensesOverAssets_3" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_OtherExpensesOverAssets_3">Other expenses for Class N shares are based on estimated amounts for the current fiscal year.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_15_lbl" xlink:to="footnote_OtherExpensesOverAssets_3" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_8" xlink:label="OtherExpensesOverAssets_2" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="OtherExpensesOverAssets_2" xlink:to="footnote_OtherExpensesOverAssets_3" />
    <link:loc xlink:type="locator" xlink:href="#Item_39" xlink:label="Item_39_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_39_lbl" xlink:to="footnote_OtherExpensesOverAssets_3" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_7" xlink:label="FeeWaiverOrReimbursementOverAssets_4" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_4" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_4">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_4" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_4" />
    <link:loc xlink:type="locator" xlink:href="#Item_16" xlink:label="FeeWaiverOrReimbursementOverAssets_5" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_5" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_5">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_5" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_5" />
    <link:loc xlink:type="locator" xlink:href="#Item_17" xlink:label="Item_17_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_17_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_5" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_18" xlink:label="Item_18_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_18_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_5" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_19" xlink:label="Item_19_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_19_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_5" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_20" xlink:label="AverageAnnualReturnSinceInception" />
    <link:footnote xlink:type="resource" xlink:label="footnote_AverageAnnualReturnSinceInception" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_AverageAnnualReturnSinceInception">The Fund was registered under the Investment Company Act of 1940 (the "1940 Act") and commenced operations on June 5, 1996. The Fund's shares were registered under the Securities Act of 1933 on March 7, 1997.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="AverageAnnualReturnSinceInception" xlink:to="footnote_AverageAnnualReturnSinceInception" />
    <link:loc xlink:type="locator" xlink:href="#Item_21" xlink:label="Item_21_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_21_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_22" xlink:label="Item_22_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_22_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_23" xlink:label="Item_23_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_23_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_26" xlink:label="AverageAnnualReturnSinceInception_2" />
    <link:footnote xlink:type="resource" xlink:label="footnote_AverageAnnualReturnSinceInception_2" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_AverageAnnualReturnSinceInception_2">  The Fund was registered under the Investment Company Act of 1940 (the "1940 Act") and commenced operations on July 1, 1994. The Fund's shares were registered under the Securities Act on March 7, 1997.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="AverageAnnualReturnSinceInception_2" xlink:to="footnote_AverageAnnualReturnSinceInception_2" />
    <link:loc xlink:type="locator" xlink:href="#Item_27" xlink:label="Item_27_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_27_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_28" xlink:label="Item_28_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_28_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_29" xlink:label="Item_29_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_29_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_9" xlink:label="FeeWaiverOrReimbursementOverAssets_6" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_6" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_6">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_6" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_6" />
    <link:loc xlink:type="locator" xlink:href="#Item_10" xlink:label="Item_10_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_10_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_6" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_11" xlink:label="Item_11_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_11_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_6" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_40" xlink:label="AverageAnnualReturnSinceInception_3" />
    <link:footnote xlink:type="resource" xlink:label="footnote_AverageAnnualReturnSinceInception_3" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_AverageAnnualReturnSinceInception_3">The Fund was registered under the Investment Company Act of 1940 (the "1940 Act") and commenced operations on January 17, 1995. The Fund's shares were registered under the Securities Act on March 7, 1997. </link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="AverageAnnualReturnSinceInception_3" xlink:to="footnote_AverageAnnualReturnSinceInception_3" />
    <link:loc xlink:type="locator" xlink:href="#Item_41" xlink:label="Item_41_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_41_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_3" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_42" xlink:label="Item_42_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_42_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_3" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_43" xlink:label="Item_43_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_43_lbl" xlink:to="footnote_AverageAnnualReturnSinceInception_3" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_30" xlink:label="FeeWaiverOrReimbursementOverAssets_7" />
    <link:footnote xlink:type="resource" xlink:label="footnote_FeeWaiverOrReimbursementOverAssets_7" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_FeeWaiverOrReimbursementOverAssets_7">Loomis, Sayles &amp; 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, 2014 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.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="FeeWaiverOrReimbursementOverAssets_7" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" />
    <link:loc xlink:type="locator" xlink:href="#Item_31" xlink:label="Item_31_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_31_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_32" xlink:label="Item_32_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_32_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_33" xlink:label="Item_33_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_33_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_34" xlink:label="Item_34_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_34_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_35" xlink:label="Item_35_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_35_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_36" xlink:label="Item_36_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_36_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_37" xlink:label="Item_37_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_37_lbl" xlink:to="footnote_FeeWaiverOrReimbursementOverAssets_7" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_4" xlink:label="ManagementFeesOverAssets_2" />
    <link:footnote xlink:type="resource" xlink:label="footnote_ManagementFeesOverAssets_2" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_ManagementFeesOverAssets_2">  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.  </link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="ManagementFeesOverAssets_2" xlink:to="footnote_ManagementFeesOverAssets_2" />
    <link:loc xlink:type="locator" xlink:href="#Item_5" xlink:label="Item_5_lbl" />
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Item_5_lbl" xlink:to="footnote_ManagementFeesOverAssets_2" use="optional" priority="0" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="#Item_38" xlink:label="Component2OtherExpensesOverAssets" />
    <link:footnote xlink:type="resource" xlink:label="footnote_Component2OtherExpensesOverAssets" xlink:role="http://www.xbrl.org/2003/role/footnote" xml:lang="en-US" id="footnote_Component2OtherExpensesOverAssets">    Other expenses include an administrative services fee of 0.25% for Admin Class shares.</link:footnote>
    <link:footnoteArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/fact-footnote" xlink:from="Component2OtherExpensesOverAssets" xlink:to="footnote_Component2OtherExpensesOverAssets" />
  </link:footnoteLink>
</xbrl>
