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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MFS Inflation-Adjusted Bond Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund’s investment objective is to seek total return that exceeds the rate of inflation over the long-term, with an emphasis on current income, but also considering capital appreciation.

Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. Expenses for Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares have been adjusted to reflect current fee arrangements. The annual fund operating expenses for Class R5 shares are based on estimated “Other Expenses” for the current fiscal year expressed as a percentage of the fund’s estimated average net assets during the period.


You may qualify for sales charge reductions if 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 or Reductions” on page 8 of the fund’s prospectus and “Waivers of Sales Charges” on page I-15 of the fund’s statement of additional information Part I.

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 2014-02-28
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 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 26% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 26.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if 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] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates The annual fund operating expenses for Class R5 shares are based on estimated "Other Expenses" for the current fiscal year expressed as a percentage of the fund's estimated average net assets during the period.
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Expenses for Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares have been adjusted to reflect current fee arrangements.
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 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] rr_ExpenseExampleByYearCaption Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

MFS (Massachusetts Financial Services Company, the fund’s investment adviser) normally invests at least 80% of the fund’s net assets in inflation-adjusted debt instruments and other investments with inflation-adjusting features.


MFS currently intends to focus the fund’s investments in inflation-adjusted debt instruments issued by the U.S. Treasury. MFS may also invest the fund’s assets in other inflation-adjusted debt instruments and non-inflation-adjusted debt instruments.


MFS generally invests substantially all of the fund’s assets in investment grade debt instruments.


MFS may invest a relatively large percentage of the fund’s assets in a single issuer or a small number of issuers.


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


While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.


MFS allocates the fund’s assets across maturities and types of debt instruments based on its evaluation of macroeconomic factors, including interest rates, inflation rates, and monetary and fiscal policies.


MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

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:


Interest Rate Risk:  The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.


Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.


U.S. Government securities not supported as to the payment of principal or interest by the U.S. Treasury are subject to greater credit risk than are U.S. Government securities supported by the U.S. Treasury.


Issuer Focus Risk:  The fund’s performance could be more volatile than the performance of more diversified funds.


Foreign Risk:  Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market.


Prepayment/Extension Risk:  Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.


Inflation-Adjusted Debt Instruments Risk:  Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.


Derivatives Risk:  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost.  Derivatives can involve leverage.


Leveraging Risk:  Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.


Investment Selection Risk:  MFS’ investment analysis 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.


Counterparty and Third Party Risk:  Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.


Liquidity Risk:  It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.

Risk Lose Money [Text] rr_RiskLoseMoney As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution 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.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_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 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 is available online at mfs.com or by calling 1-800-225-2606.

Performance Information Illustrates Variability of Returns [Text] rr_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 a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-225-2606
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress mfs.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 Class A Bar Chart.
Bar Chart Narrative [Text Block] rr_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 Closing [Text Block] rr_BarChartClosingTextBlock

During the period(s) shown in the bar chart, the highest quarterly return was 5.17% (for the calendar quarter ended March 31, 2008) and the lowest quarterly return was (3.43)% (for the calendar quarter ended September 30, 2008).

Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2008
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.17%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.43%)
Performance Table Heading rr_PerformanceTableHeading Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses or taxes
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred 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-deferred arrangements, such as 401(k) 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 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] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. 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-deferred arrangements, such as 401(k) plans or individual retirement accounts. 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.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (for the Periods Ended December 31, 2012)
Barclays U.S. Treasury Inflation Protected Securities Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays Capital U.S. Treasury Inflation Protected Securities (TIPS) Index
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 6.98%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 7.04%
Since Inception rr_AverageAnnualReturnSinceInception 6.51%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
A
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.75%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.00%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 553
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 759
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 983
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,624
Annual Return 2004 rr_AnnualReturn2004 6.42%
Annual Return 2005 rr_AnnualReturn2005 2.10%
Annual Return 2006 rr_AnnualReturn2006 (0.05%)
Annual Return 2007 rr_AnnualReturn2007 10.96%
Annual Return 2008 rr_AnnualReturn2008 (2.33%)
Annual Return 2009 rr_AnnualReturn2009 8.91%
Annual Return 2010 rr_AnnualReturn2010 5.21%
Annual Return 2011 rr_AnnualReturn2011 12.78%
Annual Return 2012 rr_AnnualReturn2012 6.01%
Label rr_AverageAnnualReturnLabel A Shares Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 0.97%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 4.97%
Since Inception rr_AverageAnnualReturnSinceInception 4.86%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
A | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel A Shares After Taxes on Distributions
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 0.12%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 3.76%
Since Inception rr_AverageAnnualReturnSinceInception 3.49%
A | After Taxes on Distributions and Sales
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel A Shares Returns After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 0.72%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 3.54%
Since Inception rr_AverageAnnualReturnSinceInception 3.34%
R4
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.75%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 230
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 407
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 921
Label rr_AverageAnnualReturnLabel R4 Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 6.15%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 6.15%
Since Inception rr_AverageAnnualReturnSinceInception 5.51%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
B
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther 4.00%
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.75%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.55%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 558
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 832
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,130
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,847
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 158
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 532
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 930
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,847
Label rr_AverageAnnualReturnLabel B Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 1.21%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 4.87%
Since Inception rr_AverageAnnualReturnSinceInception 4.67%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
C
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther 1.00%
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.75%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 268
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 541
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 940
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,054
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 168
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 541
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 940
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 2,054
Label rr_AverageAnnualReturnLabel C Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 4.09%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 5.11%
Since Inception rr_AverageAnnualReturnSinceInception 4.52%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
I
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.75%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 230
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 407
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 921
Label rr_AverageAnnualReturnLabel I Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 6.24%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 6.19%
Since Inception rr_AverageAnnualReturnSinceInception 5.57%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
R1
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.75%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 168
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 541
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 940
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,054
Label rr_AverageAnnualReturnLabel R1 Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 5.10%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 5.12%
Since Inception rr_AverageAnnualReturnSinceInception 4.44%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
R2
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.25%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.15%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 117
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 387
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 677
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,503
Label rr_AverageAnnualReturnLabel R2 Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 5.67%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 5.65%
Since Inception rr_AverageAnnualReturnSinceInception 4.95%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
R3
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.00%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.10%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.90%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 92
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 308
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 543
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,216
Label rr_AverageAnnualReturnLabel R3 Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 6.00%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 5.91%
Since Inception rr_AverageAnnualReturnSinceInception 5.23%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
R5
  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.18%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.68%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.08%) [2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.60%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 61
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 210
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 371
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 839
Label rr_AverageAnnualReturnLabel R5 Returns Before Taxes
Average Annual Returns 1 Year rr_AverageAnnualReturnYear01 6.24%
Average Annual Returns 5 Years rr_AverageAnnualReturnYear05 6.19%
Since Inception rr_AverageAnnualReturnSinceInception 5.57%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2003
[1] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.
[2] MFS Fund Distributors, Inc., has agreed in writing to waive the Class A service fee to 0.15% of the fund's average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least February 28, 2014. In addition, assets attributable to Class B shares purchased prior to May 1, 2006 are subject to the Class B service fee of 0.25% of the fund's average daily net assets annually. On assets attributable to all other Class B shares, MFS Fund Distributors, Inc., has agreed in writing to waive the Class B service fee to 0.15% of the fund's average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least February 28, 2014. In addition, Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, 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 0.80% of the fund's average daily net assets annually for Class A shares, 1.55% of the fund's average daily net assets annually for Class B shares, 1.65% of the fund's average daily net assets annually for each of Class C and Class R1 shares, 0.65% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.15% of the fund's average daily net assets annually for Class R2 shares, 0.90% of the fund's average daily net assets annually for Class R3 shares, and 0.60% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least February 28, 2014.