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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName MUTUAL OF AMERICA INVESTMENT CORP
Prospectus Date rr_ProspectusDate May 01, 2020
Small Cap Growth Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Small Cap Growth Fund May 1, 2020
Objective [Heading] rr_ObjectiveHeading Investment Objective.
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund.
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The table below describes the fees and expenses you may pay if you buy and hold Fund shares. For investments through an insurance company separate account, note that the expenses shown do not include Separate Account expenses or variable contract expenses which would increase costs if included.
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)
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 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 56.25% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 56.25%
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: (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 (d) operating expenses remain the same. For investments through an insurance company separate account, note that the expenses shown do not include Separate Account expenses or variable contract 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 Principal Investment Strategies.
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund invests primarily in growth stocks issued by companies with small sized market capitalizations that Mutual of America Capital Management LLC (the “Adviser”) believes to possess the potential for capital appreciation, based on a bottom-up fundamental stock selection process. The process includes analysis of a company’s business and financial models, as well as understanding its financial statements, to assess the potential for long-term growth in sales and cash flow. The fund will concentrate its investments in an industry or group of industries, generally to the extent that its benchmark index is also concentrated in that industry or group of industries. Currently, the Fund has a concentration in the stocks of health care and technology companies. Companies with small-sized market capitalizations are typically those companies with market capitalizations less than $5.0 billion.
  • At least 80% of the Fund’s total assets are invested in small-cap growth stocks and at least 85% of the Fund’s total assets will be invested in equity securities.
Risk [Heading] rr_RiskHeading Principal Investment Risks.
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock As with any mutual fund, loss of money is a risk of investing in the Fund. Additionally, 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.
  • 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. Events such as war, acts of terrorism, social unrest, natural disasters, public health emergencies and other unforeseen events could also significantly impact issuers, economies and markets generally.
  • 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.
  • Company risk: The price of the stock of a particular company can vary based on a variety of factors, such as the company’s financial performance, changes in management and product trends, and the potential for takeover and acquisition. The prices of equity securities of smaller companies may fluctuate more than for more established companies. The equity securities of smaller companies may not be traded as often as for larger companies, therefore it may be difficult to trade securities at a desirable price. Investments in companies with small market capitalizations generally offer greater opportunities for appreciation, but are associated with more risks than for established companies.
  • Small-Cap risk: Small-cap stocks generally are subject to greater, less predictable price changes than the securities of companies with larger market capitalizations.
  • Growth Stock risk: Growth stocks generally have above average growth potential, low dividends and high prices relative to standard measures. Growth stocks may not outperform value style investing.
  • Concentration risk: The chance that the stocks of a particular industry or group of industries will decline because of adverse developments affecting that industry. Because the Fund concentrates its assets in certain industries to approximately the same extent that its comparative Index does, the Fund bears concentration risk.
  • Health Care Industry risk: Companies in the health care industry are subject to government regulation and reimbursement rates, as well as government approval of products and services, which could have a significant effect on price and availability, and can be significantly affected by rapid obsolescence and patent expirations.
  • Technology Industry risk: Companies in the technology industries can be significantly affected by obsolescence of existing technology, short product cycles, falling prices and profits, competition from new market entrants, and general economic conditions.
  • Stock risk: The value of your investment will go up or down, depending on movements in the stock markets. The investment results may be better or worse than the results for the stock markets taken as a whole, or than the results of other funds that invest in the same types of securities.
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 Performance/Annual Return.
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 year and the life of the Fund 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.

For investments through an insurance company separate account, note that 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. 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 year and the life of the Fund 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 For investments through an insurance company separate account, note that 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   
Fourth quarter 2010
      17.06 % 
Worst   
Third quarter 2011
      (20.42 )% 
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for periods ended December 31, 2019)
Small Cap Growth Fund | Small Cap Growth Fund Class  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther
Management Fees rr_ManagementFeesOverAssets 0.75%
Other Expenses rr_OtherExpensesOverAssets 0.06%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.81%
1 Year rr_ExpenseExampleYear01 $ 83
3 Years rr_ExpenseExampleYear03 262
5 Years rr_ExpenseExampleYear05 459
10 Years rr_ExpenseExampleYear10 1,044
1 Year rr_ExpenseExampleNoRedemptionYear01 83
3 Years rr_ExpenseExampleNoRedemptionYear03 262
5 Years rr_ExpenseExampleNoRedemptionYear05 459
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,044
2010 rr_AnnualReturn2010 33.27%
2011 rr_AnnualReturn2011 (2.28%)
2012 rr_AnnualReturn2012 5.62%
2013 rr_AnnualReturn2013 41.19%
2014 rr_AnnualReturn2014 5.70%
2015 rr_AnnualReturn2015 (2.39%)
2016 rr_AnnualReturn2016 8.10%
2017 rr_AnnualReturn2017 23.82%
2018 rr_AnnualReturn2018 (12.53%)
2019 rr_AnnualReturn2019 26.59%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.06%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.42%)
Past One Year rr_AverageAnnualReturnYear01 26.59%
Past Five Years rr_AverageAnnualReturnYear05 7.66%
Past Ten Years rr_AverageAnnualReturnYear10 11.48%
Small Cap Growth Fund | Russell 2000 Growth® Index (Index reflects no deduction for fees and expenses)  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 28.48%
Past Five Years rr_AverageAnnualReturnYear05 9.34%
Past Ten Years rr_AverageAnnualReturnYear10 13.01%