The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund Complex. More information about these and other discounts is available from your financial professional and in the section "How Sales Charges Are Calculated" on page 36 of the Prospectus and on page 106 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 16% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

16.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If shares are redeemed

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If shares are not redeemed

Strategy [Heading]

rr_StrategyHeading

Investments, Risks and Performance Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest primarily in equity securities, including common stocks, convertible securities and warrants. The Fund focuses on stocks of large capitalization companies, but the Fund may invest in companies of any size. The Fund normally invests across a wide range of sectors and industries. The Fund's portfolio manager employs a growth style of equity management that emphasizes companies with sustainable competitive advantages, secular long-term cash flow growth returns on invested capital above their cost of capital and the ability to manage for profitable growth that can create long-term value for shareholders. The Fund's portfolio manager aims to invest in companies when they trade at a significant discount to the estimate of intrinsic value. The Fund will consider selling a portfolio investment when the portfolio manager believes the issuer's investment fundamentals are beginning to deteriorate, when the investment no longer appears consistent with the portfolio manager's investment methodology, when the Fund must meet redemptions, in order to take advantage of more attractive investment opportunities, or for other investment reasons which the portfolio manager deems appropriate. The Fund may also invest any portion of its assets in equity securities of Canadian issuers, up to 20% of its assets in other foreign securities, including emerging market securities, engage in foreign currency transactions, invest in options for hedging and investment purposes and invest in Rule 144A securities. The Adviser may elect not to hedge currency risk, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged. Except as provided above, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money by investing in the Fund. Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged. Derivatives Risk: Derivatives are subject to changes in the value of the underlying asset or indices on which such transactions are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities markets values, interest rates or currency exchange rates. It is possible that the Fund's liquid assets may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. The Fund's use of derivatives such as forward currency contracts and options transactions involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for forward currency contracts and other over-the-counter traded derivatives), the risk of difficulties in pricing and valuation, the risk that changes in the value of a derivative may not correlate perfectly with relevant assets, rates or indices, liquidity risk, allocation risk and the risk of losing more than the initial margin required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. Although Loomis Sayles monitors the creditworthiness of the Fund's derivative counterparties, there can be no assurance that the Fund's derivative counterparties will not experience similar financial difficulties, possibly resulting in losses to the Fund. Emerging Markets Risk: Investing in emerging markets companies, 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 companies 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. Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. Rule 144A securities may be less liquid than other equity securities. Growth stocks are generally more sensitive to market movements than other types of stocks primarily because their stock prices are based heavily on future expectations. If the Adviser's assessment of the prospects for a company's growth is wrong, or if the Adviser's judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that the Adviser has placed on it. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer's bonds and preferred stock generally take precedence over the claims of those who own common stock. Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit and information risks. The Fund's investments in foreign securities are also subject to foreign currency fluctuations. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity. Issuer Risk: The value of the Fund's investments may decline for a number of reasons that directly relate to the issuer, such as management performance, financial leverage and reduced demand for the issuer's goods and services. Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices that multiply small index, market or asset price movements into larger changes in value. 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. The use of leverage increases the impact of gains and losses on a fund's returns, and may lead to significant losses if investments are not successful. However, the Adviser will attempt to ensure that at all times the Fund has sufficient liquid assets to enable it to satisfy its obligations under its derivative contracts. Liquidity Risk: Liquidity risk exists when particular investments are difficult to purchase or sell, possibly preventing the Fund from selling these illiquid securities at an advantageous price or time. A lack of liquidity also may cause the value of investments to decline. Illiquid investments also may be difficult to value. Management Risk: A strategy used by the Fund's portfolio manager may fail to produce the intended result. Market Risk: 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. Small Capitalization Risk: The general risks associated with corporate income-producing securities are particularly pronounced for securities issued by companies with smaller market capitalizations. These companies may have limited product lines, markets or financial resources or they may depend on a few key employees. As a result, they may be subject to greater levels of credit, market and issuer risk. Securities of smaller companies may trade less frequently and in lesser volume than more widely-held securities and their values may fluctuate more sharply than other securities. Further, securities of smaller companies may perform differently in different cycles than securities of larger companies. Companies with medium-sized market capitalizations may have risks similar to those of smaller companies.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year and ten-year periods compare to those of a broad measure of market performance. The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated performance information is available online at ngam.natixis.com and/or by calling the Fund toll-free at 800-225-5478.The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund's shares. A sales charge will reduce your return.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

ngam.natixis.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Total Returns for Class A Shares

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund's shares.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Quarterly Return:
Third Quarter 2010, 14.73%

Lowest Quarterly Return:
Fourth Quarter 2008, -26.00%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns
(for the periods ended December 31, 2011)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

In some cases the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

Class B total returns in the table below do not reflect the automatic conversion of Class B shares to Class A shares after eight years.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The returns shown in the chart and table for Class A shares prior to September 15, 2003 are those of Retail Class shares, which were redesignated as Class A shares, restated to reflect the sales loads of Class A shares. Prior to the inception of Class B and Class C shares (September 12, 2003), performance is that of Institutional Class shares, which were redesignated as Class Y shares, restated to reflect the higher net expenses and sales loads of Class B shares and Class C shares, respectively. Prior to February 1, 2012, Class Y shares were offered in a separate prospectus and given that Class Y shares are now offered in this multi-class prospectus, Total Return, Return After Taxes on Distributions and Return After Taxes on Distributions & Sale of Fund Shares are now presented for Class A Shares.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-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 only one class of the Fund. After-tax returns for the other classes of the Fund will vary. In some cases the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Loomis Sayles Growth Fund | Russell 1000 Growth Index

Risk/Return:

rr_RiskReturnAbstract

Past 1 Year

rr_AverageAnnualReturnYear01

2.64%

Past 5 Years

rr_AverageAnnualReturnYear05

2.50%

Past 10 Years

rr_AverageAnnualReturnYear10

2.60%

[1]

Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 1.25%, 2.00%, 2.00% and 1.00% of the Fund's average daily net assets for Class A, B, C and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2013 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 1.25%, 2.00%, 2.00% and 1.00% of the Fund's average daily net assets for Class A, B, C and Y 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.