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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName MUTUAL OF AMERICA INVESTMENT CORP
Prospectus Date rr_ProspectusDate May 01, 2019
Mid-Term Bond Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <b>Mid-Term Bond Fund May 1, 2019</b>
Objective [Heading] rr_ObjectiveHeading <b>Investment Objective.</b>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The primary investment objective of the Fund is to produce a high level of current income.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock The secondary investment objective is the preservation of shareholders’ capital.
Expense [Heading] rr_ExpenseHeading <b>Fees and Expenses of the Fund.</b>
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The table below describes the fees and expenses you may pay if you buy and hold Fund shares. The expenses shown do not include Separate Account expenses which would increase costs if included.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <b>Shareholder Fees </b> (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <b>Annual Fund Operating Expenses</b><br/><b>(expenses that you pay each year as a percentage of the value of your investment)</b>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <b>Portfolio Turnover.</b>
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 result in higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the Fund’s most recently completed fiscal year, the Fund’s portfolio turnover rate was 20.12% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 20.12%
Expense Example [Heading] rr_ExpenseExampleHeading <b>Example.</b>
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: (a) that you invest $10,000 in the Fund for the time periods indicated and then redeem or hold all of your shares at the end of those periods, (b) a 5% return each year and (c) operating expenses remain the same. The expenses shown do not include Separate Account expenses which would increase costs if included. Although your actual costs may be higher or lower, your cost based on these assumptions would be:
Strategy [Heading] rr_StrategyHeading <b>Principal Investment Strategies.</b>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund invests primarily in publicly-traded, investment-grade debt securities.
  • At least 80% of the Fund’s total assets are invested in investment-grade securities issued by U.S. corporations or by the U.S. Government or its agencies, such as bonds, notes, debentures, zero coupon securities and mortgage-backed securities. Bonds are debt instruments that can be issued by the federal government, government agencies and subdivisions, states, cities, corporations and other institutions.
  • Although the Fund only purchases investment-grade bonds, the Fund may continue to hold certain corporate bonds in the Fund’s portfolio that are downgraded to below investment grade, commonly referred to as “high yield” or “junk bonds.”
  • The Adviser evaluates each security to be purchased and selects securities based on duration, seeking to maintain duration for the Fund overall within +/- 10% of the duration of its benchmark; credit quality as determined by fundamental financial analysis focused on the issuer’s ability to repay debt; and interest income anticipated to be generated.
  • The Fund’s securities holdings will have an average maturity of three to seven years.
Risk [Heading] rr_RiskHeading <b>Principal Investment Risks.</b>
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock An investment in the Fund is subject to the following risks which are described in more detail in the Prospectus.
  • General risk: The Fund may not achieve its investment objective. An investment in the Fund could decline in value, and you could lose money by investing in the Fund.
  • Active Management risk: The portfolio manager’s judgments about the attractiveness, value or potential appreciation of the Fund’s investments may prove to be incorrect. The Fund could underperform in comparison to other funds with a similar benchmark or similar objectives and investment strategies if the Fund’s overall investment selections or strategies fail to produce the intended results.
  • Market risk: The risk that prices of securities will go down because of the interplay of market forces may affect a single issuer, industry or sector of the economy or may affect the market as a whole.
  • Mortgage risk: The duration of mortgage-related securities and interest rates tend to move together. As interest rates rise, the duration of mortgage-related securities extends and as interest rates fall, mortgage-related securities are often prepaid at a faster rate. Because of interest rate changes, it is not possible to predict the realized yield or average life of a mortgage-backed security.
  • Zero Coupon risk: Zero coupon securities and discount notes do not pay interest prior to maturity and therefore may be more difficult to sell during periods of interest rate changes. The market value of debt securities declines as interest rates rise; therefore the Fund may lose value if it sells zero coupon securities prior to their maturity date.
  • Interest Rate risk: Securities may lose value as the interest rate changes because bonds tend to decrease in value as interest rates rise. In general, the longer the term to maturity, the greater impact interest rate changes will have on the value of a security. The Fund faces a heightened level of interest rate risk under current conditions because interest rates are at near historically low levels.
  • Corporate Debt risk: During periods of economic uncertainty, the value of corporate debt securities may decline relative to the value of U.S. government debt securities.
  • Credit risk: Debt obligations are generally subject to the risk that the issuer may be unable to make principal and interest payments when they are due.
  • Call risk: When interest rates decline, an issuer may have an option to call the securities before maturity, resulting in reduced income.
  • Non-investment grade debt risk: Non-investment grade debt obligations, known as “high yield” or “junk bonds,” have a higher risk of default and tend to be less liquid than higher-rated securities.
  • Liquidity risk: The prices of debt securities may be subject to significant volatility, particularly as markets become less liquid due to limited dealer inventory of corporate bonds.
  • Extension risk: Mortgage-related and other asset-backed securities are subject to the risk that the issuer of such a security pays back the principal of such an obligation later than expected. This may occur when interest rates rise, and this may negatively affect Fund returns.
  • Prepayment risk: Mortgage-related and other asset-backed securities are subject to the risk that the issuer of such a security pays back the principal of such an obligation earlier than expected. This may occur when interest rates decline, and may negatively affect Fund returns.
Risk Lose Money [Text] rr_RiskLoseMoney An investment in the Fund could decline in value, and you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <b>Performance/Annual Return.</b>
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table below show the annual return and average annual returns of the Fund.

Below the bar chart are the Fund’s highest and lowest total returns for any calendar quarter during the period covered by the chart, showing the volatility of the Fund’s total returns. The numbers in parentheses are negative, representing a loss of principal.

The information indicates some 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 one, five, and ten years compare to those of a broad-based, unmanaged index for those periods. A fund’s past performance does not necessarily indicate how it will perform in the future.

The total returns and average annual total returns shown do not include charges against the assets of the Separate Accounts that purchase Fund shares. If these charges were reflected, returns would be less than those shown. Updated performance information is available at no cost online at http://www.mutualofamerica.com or by calling 1-800-468-3785.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below show the annual return and average annual returns of the Fund. <br/><br/> The information indicates some 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 one, five, and ten years compare to those of a broad-based, unmanaged index for those periods.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-468-3785
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress http://www.mutualofamerica.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture A fund’s past performance does not necessarily indicate how it will perform in the future.
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The total returns and average annual total returns shown do not include charges against the assets of the Separate Accounts that purchase Fund shares. If these charges were reflected, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Best and Worst Performing Quarters

     Quarter/Year    Total Return  
Best   
Third quarter 2009
      4.16 % 
Worst   
Second quarter 2013
      (1.94 )% 
Performance Table Heading rr_PerformanceTableHeading <b>Average Annual Total Returns (for periods ended December 31, 2018)</b>
Mid-Term Bond Fund | Mid-Term Bond Fund Class  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther
Management Fees rr_ManagementFeesOverAssets 0.40%
Other Expenses rr_OtherExpensesOverAssets 0.05%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.45%
1 Year rr_ExpenseExampleYear01 $ 46
3 Years rr_ExpenseExampleYear03 146
5 Years rr_ExpenseExampleYear05 255
10 Years rr_ExpenseExampleYear10 580
1 Year rr_ExpenseExampleNoRedemptionYear01 46
3 Years rr_ExpenseExampleNoRedemptionYear03 146
5 Years rr_ExpenseExampleNoRedemptionYear05 255
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 580
2009 rr_AnnualReturn2009 11.22%
2010 rr_AnnualReturn2010 6.93%
2011 rr_AnnualReturn2011 6.34%
2012 rr_AnnualReturn2012 3.33%
2013 rr_AnnualReturn2013 (0.55%)
2014 rr_AnnualReturn2014 3.22%
2015 rr_AnnualReturn2015 0.61%
2016 rr_AnnualReturn2016 3.51%
2017 rr_AnnualReturn2017 2.32%
2018 rr_AnnualReturn2018 0.57%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <b>Best</b>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.16%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <b>Worst</b>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.94%)
Past One Year rr_AverageAnnualReturnYear01 0.57%
Past Five Years rr_AverageAnnualReturnYear05 2.04%
Past Ten Years rr_AverageAnnualReturnYear10 3.70%
Mid-Term Bond Fund | Bloomberg Barclays U.S. Intermediate Government/Credit Bond Index (Index reflects no deduction for fees and expenses)  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 0.88%
Past Five Years rr_AverageAnnualReturnYear05 1.86%
Past Ten Years rr_AverageAnnualReturnYear10 2.90%