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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Equity Index Fund May 1, 2013
Objective [Heading] rr_ObjectiveHeading Investment Objective.
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks investment results that correspond to the investment performance of the S&P 500® Index.

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. The expenses shown do not include Separate Account expenses which would increase costs if included.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment) N/A
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 6.45% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 6.45%
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 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.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption 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 primarily invests in the 500 common stocks included in the S&P 500® Index to replicate, to the extent practicable, the weightings of such stocks in the Index. The Fund also purchases futures contracts on the S&P 500® Index to invest available cash prior to the purchase of common stocks.

Risk [Heading] rr_RiskHeading Principal Investment Risks.
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.


•  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.


•  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.


•  Index risk: The Fund's investment performance may not precisely duplicate the performance of the index. The Fund may rebalance the portfolio to account for changes in the composition of the index or in the valuations of the stocks within the index.


•  Large Cap risk: Larger, more established companies may be unable to respond quickly to new competitive challenges and also may not be able to attain the high growth rate of successful smaller companies.


•  Mid-Cap risk: Mid-cap stocks experience more market risk and sharper price fluctuations than for large-cap stocks due to the fact that the earnings of mid-size companies tend to be less predictable and the stocks are traded less frequently. At times it may be difficult for a Fund to sell mid-cap stocks at a price equal to their value.


•  Options and Futures risk: Securities held in the Fund may not be exactly the same as securities in the underlying options or futures contracts and as a result the price of the securities being hedged may not move in the same amount or direction as the underlying index, securities or debt obligation. When the Fund purchases an option, it may lose the entire premium plus costs. When an option is exercised the Fund may be required to sell the security at a price below its market value.


•  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. It may be more difficult for the Fund to sell a small capitalization stock or any stock that trades "over-the-counter", than a larger capitalization stock or stocks that trade on a national or regional stock exchange.

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, 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.
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 Closing [Text Block] rr_BarChartClosingTextBlock

Best and Worst Performing Quarters


   

Quarter/Year

 

Total Return

 

Best

 

Second quarter 2009

   

15.82

%

 

Worst

 

Fourth quarter 2008

   

(21.87

)%

 
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.82%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.87%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (Index reflects no deduction of any charges against the assets)
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (for periods ended December 31, 2012)
S&P 500® Index (Index reflects no deduction of any charges against the assets)
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.00%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.66%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 7.10%
Equity Index Fund Class
  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.08%
Other Expenses rr_OtherExpensesOverAssets 0.14%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.22%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 23
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 71
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 125
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 284
Annual Return 2003 rr_AnnualReturn2003 28.32%
Annual Return 2004 rr_AnnualReturn2004 10.69%
Annual Return 2005 rr_AnnualReturn2005 4.81%
Annual Return 2006 rr_AnnualReturn2006 15.59%
Annual Return 2007 rr_AnnualReturn2007 5.22%
Annual Return 2008 rr_AnnualReturn2008 (37.08%)
Annual Return 2009 rr_AnnualReturn2009 26.13%
Annual Return 2010 rr_AnnualReturn2010 14.68%
Annual Return 2011 rr_AnnualReturn2011 1.88%
Annual Return 2012 rr_AnnualReturn2012 15.94%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.94%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.46%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.89%