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Label Element Value
MFS Blended Research Mid Cap Equity Fund  
Risk/Return: oef_RiskReturnAbstract  
Risk/Return [Heading] oef_RiskReturnHeading MFS® Blended Research® Mid Cap Equity Fund Summary of Key Information
Objective [Heading] oef_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] oef_ObjectivePrimaryTextBlock

The fund’s investment objective is to seek capital appreciation.

Expense Heading [Optional Text] oef_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] oef_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below. Expenses for Class R1 shares have been adjusted to reflect the full impact of the distribution fee.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 11 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

Shareholder Fees Caption [Optional Text] oef_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Optional Text] oef_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Portfolio Turnover [Heading] oef_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] oef_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 when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 51% of the average value of its portfolio.
Portfolio Turnover, Rate oef_PortfolioTurnoverRate 51.00%
Expense Breakpoint Discounts [Text] oef_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] oef_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] oef_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] oef_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 you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] oef_ExpenseExampleByYearCaption Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Strategy [Heading] oef_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] oef_StrategyNarrativeTextBlock

MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund's objective by actively identifying potential investments based on fundamental and quantitative analysis and then constructing a portfolio from these potential investments while managing various risk factors (e.g., issuer, industry, and sector weightings, market capitalization, and volatility) compared to the Russell Midcap® Index.

MFS normally invests at least 80% of the fund’s net assets in equity securities of issuers with medium market capitalizations. MFS defines medium market capitalization companies as issuers that (i) have market capitalizations within the capitalization range of the Russell Midcap® Index over the past 12 months based on the current composition of the index and/or are (ii) classified as a medium capitalization company by an independent third party financial data provider. The market capitalization range of companies considered to have medium capitalizations based on the above criteria will change over time depending on market conditions. For illustrative purposes, as of August 31, 2026, the range of the market capitalizations of the issuers in the Russell Midcap® Index was between approximately $2.0 billion and $114.9 billion, and the fund's average weighted market capitalization as of that date was $28.1 billion. Equity securities include common stocks, depositary receipts, equity interests in real estate investment trusts (REITs), and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer.

In selecting investments for the fund, MFS is not constrained by any particular investment style. MFS may invest the fund’s assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies.

MFS may invest the fund’s assets in foreign securities.

MFS normally invests the fund's assets across different industries and sectors, but MFS may invest a significant percentage of the fund's assets in issuers in a single industry or sector.

MFS uses an active bottom-up approach to buying and selling investments for the fund. Investments are selected primarily based on blending fundamental and quantitative research. MFS uses fundamental analysis of individual issuers, which takes into account factors such as an issuer’s financial condition and market, economic, political, and regulatory conditions, to determine a fundamental rating for an issuer. MFS uses quantitative analysis to systematically evaluate an issuer’s valuation, price and earnings momentum, earnings quality, and other factors, in determining a quantitative rating for an issuer. MFS combines the fundamental rating with the quantitative rating to create a blended rating for an issuer. When the fundamental rating is not available, MFS treats the issuer as having a neutral fundamental rating.

MFS constructs the portfolio using a portfolio optimization process that considers the blended rating, as well as issuer, industry, and sector weightings, market capitalization, volatility, and other factors. The portfolio managers have the discretion to adjust the inputs and parameters used in the optimization process and the fund's portfolio holdings based on factors such as the desired portfolio characteristics and the portfolio managers’ qualitative assessment of the optimization results. MFS' goal is to construct an actively managed portfolio with a target predicted tracking error of approximately 3% compared to the Russell Midcap® Index. Tracking error generally measures how the differences between the fund's returns and the Russell Midcap® Index's returns have varied over a period of time.

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block] fnd_NmRule35d1TermDfnSmryTextBlock MFS defines medium market capitalization companies as issuers that (i) have market capitalizations within the capitalization range of the Russell Midcap® Index over the past 12 months based on the current composition of the index and/or are (ii) classified as a medium capitalization company by an independent third party financial data provider. The market capitalization range of companies considered to have medium capitalizations based on the above criteria will change over time depending on market conditions. For illustrative purposes, as of August 31, 2026, the range of the market capitalizations of the issuers in the Russell Midcap® Index was between approximately $2.0 billion and $114.9 billion, and the fund's average weighted market capitalization as of that date was $28.1 billion. Equity securities include common stocks, depositary receipts, equity interests in real estate investment trusts (REITs), and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer.
Summary of Selection Criteria for Rule 35d-1 Term in Fund Name [Text Block] fnd_NmRule35d1TermSlctnCritSmryTextBlock MFS defines medium market capitalization companies as issuers that (i) have market capitalizations within the capitalization range of the Russell Midcap® Index over the past 12 months based on the current composition of the index and/or are (ii) classified as a medium capitalization company by an independent third party financial data provider. The market capitalization range of companies considered to have medium capitalizations based on the above criteria will change over time depending on market conditions. For illustrative purposes, as of August 31, 2026, the range of the market capitalizations of the issuers in the Russell Midcap® Index was between approximately $2.0 billion and $114.9 billion, and the fund's average weighted market capitalization as of that date was $28.1 billion. Equity securities include common stocks, depositary receipts, equity interests in real estate investment trusts (REITs), and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer.
Rule 35d-1 Eighty Percent Investment Policy [Text Block] fnd_NmRule35d1EightyPctInvstmntPlcyTextBlock MFS normally invests at least 80% of the fund’s net assets in equity securities of issuers with medium market capitalizations.
Bar Chart and Performance Table [Heading] oef_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] oef_PerformanceNarrativeTextBlock

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Information Illustrates Variability of Returns [Text] oef_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Performance Availability Phone [Text] oef_PerformanceAvailabilityPhone 1-800-225-2606
Performance Availability Website Address [Text] oef_PerformanceAvailabilityWebSiteAddress mfs.com
Performance Past Does Not Indicate Future [Text] oef_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] oef_BarChartHeading Class A Bar Chart.
Bar Chart Narrative [Text Block] oef_BarChartNarrativeTextBlock The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] oef_BarChartDoesNotReflectSalesLoads The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Closing [Text Block] oef_BarChartClosingTextBlock

The total return for the six-month period ended June 30, 2026, was 18.79%. During the period(s) shown in the bar chart, the highest quarterly return was 21.42% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (27.06)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading oef_PerformanceTableHeading Performance Table.
Index No Deduction for Fees, Expenses, or Taxes [Text] oef_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses, or taxes
Performance Table Not Relevant to Tax Deferred oef_PerformanceTableNotRelevantToTaxDeferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance Table One Class of after Tax Shown [Text] oef_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Table Closing [Text Block] oef_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Average Annual Return, Caption [Optional Text] oef_AverageAnnualReturnCaption Average Annual Total Returns (For the Periods Ended December 31, 2025)
MFS Blended Research Mid Cap Equity Fund | Principal Risks  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Principal Risks

As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:
MFS Blended Research Mid Cap Equity Fund | Risk Lose Money [Member]  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
MFS Blended Research Mid Cap Equity Fund | Risk Not Insured [Member]  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
MFS Blended Research Mid Cap Equity Fund | Investment Selection Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Investment Selection Risk: MFS' investment analysis, its development and use of quantitative models, and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests. The quantitative models used by MFS (both proprietary and third-party) may not produce the intended results for a variety of reasons, including the factors used

in the models, the weight placed on each factor in the models, changes from the market factors' historical trends, changing sources of market return or market risk, and technical issues in the design, development, implementation, application, and maintenance of the models (e.g., incomplete, stale, or inaccurate data, human error, programming or other software issues, coding errors, and technology failures).
MFS Blended Research Mid Cap Equity Fund | Equity Market Risk/Company Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Equity Market Risk/Company Risk: Equity markets are volatile and can decline significantly in response to changes in, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the equity markets in general. Certain events can have a dramatic adverse effect on equity markets and may lead to periods of high volatility in an equity market or a segment of an equity market. The value of an investment held by the fund may decline due to factors directly related to the issuer.
MFS Blended Research Mid Cap Equity Fund | Growth Company Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Growth Company Risk: The stocks of growth companies can be more sensitive to the company’s earnings and more volatile than the market in general.
MFS Blended Research Mid Cap Equity Fund | Value Company Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.
MFS Blended Research Mid Cap Equity Fund | Mid Cap Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Mid Cap Risk: The stocks of mid cap companies can be more volatile and their shares can be less liquid than those of larger companies.
MFS Blended Research Mid Cap Equity Fund | Investment Strategy Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Investment Strategy Risk: There is no assurance that the fund's predicted tracking error will equal its target predicted tracking error at any point in time or consistently for any period of time, or that the fund's predicted tracking error and actual tracking error will be similar. The fund's strategy to target a predicted tracking error of approximately 3% compared to the Russell Midcap® Index and to blend fundamental and quantitative research may not produce the intended results. In addition, MFS' fundamental research is not available for all issuers.
MFS Blended Research Mid Cap Equity Fund | Foreign Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Foreign Risk: Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These factors can make foreign investments, especially those tied economically to countries with developing economies or countries subject to sanctions or the threat of new or modified sanctions, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market.
MFS Blended Research Mid Cap Equity Fund | REITs Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

REITs Risk: The risks of investing in REITs include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; difficulties in valuing and disposing of real estate; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; the management skill and creditworthiness of the REIT manager; and other factors. The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.
MFS Blended Research Mid Cap Equity Fund | Focus Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Focus Risk: Issuers in a single industry, sector, country, or region can react similarly to market, currency, political, economic, regulatory, geopolitical, environmental, public health, and other conditions, and the fund's performance will be affected by the conditions in the industries, sectors, countries, and regions to which the fund is exposed. Furthermore, investments in particular industries, sectors, countries, or regions may be more volatile than the broader market as a whole.

MFS Blended Research Mid Cap Equity Fund | Liquidity Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Liquidity Risk: It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs.

MFS Blended Research Mid Cap Equity Fund | Large Shareholder Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Large Shareholder Risk: From time to time, shareholders of the fund (which may include institutional investors, financial intermediaries, or other MFS funds) may make relatively large redemptions or purchases of fund shares. These transactions may cause the fund to sell securities or invest additional cash, as the case may be, at disadvantageous prices. Redemptions of a large number of shares also may increase transaction and other costs or have adverse tax consequences for shareholders of the fund by requiring a sale of portfolio securities. Purchases of a large number of shares may adversely affect the fund's performance to the extent that it takes time to invest new cash and the fund maintains a larger cash position than it ordinarily would.
MFS Blended Research Mid Cap Equity Fund | Russell 3000® Index  
Risk/Return: oef_RiskReturnAbstract  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Russell 3000® Index
Average Annual Return, Percent oef_AvgAnnlRtrPct 17.15%
Average Annual Return, Percent oef_AvgAnnlRtrPct 13.15%
Average Annual Return, Percent oef_AvgAnnlRtrPct 14.30%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Russell Midcap® Index  
Risk/Return: oef_RiskReturnAbstract  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Russell Midcap® Index
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.60%
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.67%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.58%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1]
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.88%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.84%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expenses Deferred Charges [Text Block] oef_ExpensesDeferredChargesTextBlock This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 656
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 836
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 1,031
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,594
Year to Date Return, Label [Optional Text] oef_YearToDateReturnLabel The total return for the six-month period ended
Bar Chart, Year to Date Return, Date oef_BarChartYearToDateReturnDate Jun. 30, 2026
Bar Chart, Year to Date Return oef_BarChartYearToDateReturn 18.79%
Highest Quarterly Return, Label [Optional Text] oef_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date oef_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return oef_BarChartHighestQuarterlyReturn 21.42%
Lowest Quarterly Return, Label [Optional Text] oef_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date oef_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return oef_BarChartLowestQuarterlyReturn (27.06%)
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.56%
Average Annual Return, Percent oef_AvgAnnlRtrPct 9.46%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.10%
Annual Return [Percent] oef_AnnlRtrPct 18.81%
Annual Return [Percent] oef_AnnlRtrPct (11.41%)
Annual Return [Percent] oef_AnnlRtrPct 29.97%
Annual Return [Percent] oef_AnnlRtrPct 10.10%
Annual Return [Percent] oef_AnnlRtrPct 26.43%
Annual Return [Percent] oef_AnnlRtrPct (13.93%)
Annual Return [Percent] oef_AnnlRtrPct 19.41%
Annual Return [Percent] oef_AnnlRtrPct 19.04%
Annual Return [Percent] oef_AnnlRtrPct 7.76%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class A | After Taxes on Distributions  
Risk/Return: oef_RiskReturnAbstract  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns After Taxes on Distributions
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.91%
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.21%
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.37%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class A | After Taxes on Distributions and Sales  
Risk/Return: oef_RiskReturnAbstract  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.41%
Average Annual Return, Percent oef_AvgAnnlRtrPct 6.89%
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.70%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSBX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.63%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.59%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 562 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 810 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 1,083 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,729 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 162 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 510 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 883 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,729 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.95%
Average Annual Return, Percent oef_AvgAnnlRtrPct 9.65%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.09%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.63%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.59%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 262 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 510 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 883 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,729 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 162 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 510 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 883 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,729 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.98%
Average Annual Return, Percent oef_AvgAnnlRtrPct 9.92%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.08%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSLX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.63%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.59%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 198
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 347
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 783
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.05%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.04%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.08%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class R1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.63%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.59%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 162
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 510
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 883
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,929
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.70%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.08%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class R2  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSSX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.13%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.09%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 111
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 355
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 618
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,371
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.42%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.48%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.52%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class R3  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSTX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.88%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.84%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 86
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 277
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 484
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,081
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.70%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.75%
Average Annual Return, Percent oef_AvgAnnlRtrPct 10.80%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class R4  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSVX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.14%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.63%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.59%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 198
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 347
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 783
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.01%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.04%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.08%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
MFS Blended Research Mid Cap Equity Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol BMSYX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.54%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.03%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.51%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 52
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 170
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 299
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 674
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.16%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 11.17%
Performance Inception Date oef_PerfInceptionDate Aug. 19, 2016
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
[2] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least September 30, 2027. MFS has agreed in writing to bear the fund’s expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund’s investment activity), such that “Total Annual Fund Operating Expenses” do not exceed 0.84% of the class' average daily net assets annually for each of Class A and Class R3 shares, 1.59% of the class' average daily net assets annually for each of Class B, Class C, and Class R1 shares, 0.59% of the class' average daily net assets annually for each of Class I and Class R4 shares, 1.09% of the class' average daily net assets annually for Class R2 shares, and 0.51% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least September 30, 2027.
[3] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.