Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName GAMCO INTERNATIONAL GROWTH FUND, INC
Prospectus Date rr_ProspectusDate Apr. 30, 2018
GAMCO INTERNATIONAL GROWTH FUND, INC  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SUMMARY OF THE FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks to provide investors with long term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund:
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Fund. More information about these and other discounts is available from your financial professional and in the section entitled, “Classes of Shares” on page 11 of the prospectus and in Appendix A, “Sales Charge Reductions and Waivers Available through Certain Intermediaries,” attached to the Fund’s prospectus.
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 April 30, 2019
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 Fund shares are held in a taxable account. These costs, which are not reflected in the 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 4% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 4.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Fund.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Expense 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 then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same (taking into account the expense limitation agreement until April 30, 2019 with respect to Class I shares). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares of the Fund:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock Under normal circumstances, the Fund invests at least 65% of its total assets in equity securities of foreign issuers located in at least three countries outside the United States that Gabelli Funds, LLC (the “Adviser”) believes are likely to have rapid growth in revenues and earnings and potential for above-average capital appreciation. Equity securities include common and preferred stocks, securities convertible into common stocks and securities such as rights and warrants that have common stock characteristics. The Fund seeks to invest in companies that have the potential to grow faster than other companies in their respective equity markets and are priced at attractive valuation levels.

The Fund intends to diversify its investments across different countries. The percentage of Fund assets invested in particular countries or regions will change from time to time based on the Adviser’s judgment. The Fund intends to invest in the securities of companies located in developed countries and, to a lesser extent, those located in emerging markets.

The Adviser may sell a holding if its fundamentals deteriorate or change in a way, as determined by the Adviser, that the investment case for the holding is no longer appropriate for the Fund.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock You may want to invest in the Fund if:
  • you are a long term investor
  • you seek growth of capital
  • you seek to diversify domestic investments with investments in foreign securities
The Fund’s share price will fluctuate with changes in the market value of the Fund’s portfolio securities. Your investment in the Fund is not guaranteed; you may lose money by investing in the Fund. When you sell Fund shares, they may be worth more or less than what you paid for them.

The principal risks presented by the Fund are:
  • Convertible Securities Risk.    Convertible securities provide higher yields than the underlying common stock, but generally offer lower yields than nonconvertible securities of similar quality. The value of convertible securities fluctuates in relation to changes in interest rates and, in addition, fluctuates in relation to the underlying common stock.
  • Equity Market Risk.    The price of equity securities may rise or fall because of changes in the broad market or changes in a company’s financial condition, sometimes rapidly or unpredictably. These price movements may result from factors affecting individual companies, sectors or industries selected for the Fund’s portfolio or the securities market as a whole, such as changes in economic or political conditions. When the value of the Fund’s securities goes down, your investment in the Fund decreases in value.
  • Foreign Securities Risk.    Investments in foreign securities involve risks relating to political, social, and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and foreign issuers and markets are subject. These risks include expropriation, differing accounting and disclosure standards, currency exchange risks, settlement difficulties, market illiquidity, difficulties enforcing legal rights, and greater transaction costs. These risks are more pronounced in the securities of companies located in emerging markets.
  • Issuer-Specific Risk.    The value of an individual security or particular type of security can be more volatile than the market as a whole and can perform differently from the market as a whole. The Fund could lose all of its investment in a company’s securities.
  • Large-Capitalization Risk.    Larger, more established companies may be unable to respond quickly to new competitive challenges such as changes in technology and consumer tastes. Many larger companies also may not be able to attain the high growth rate of successful smaller companies, especially during extended periods of economic expansion.
  • Management Risk.    If the portfolio manager is incorrect in his assessment of the growth prospects of the securities the Fund holds, then the value of the Fund’s shares may decline.
  • Market Risk.    The risk that the securities markets will move down, sometimes rapidly and unpredictably based on overall economic conditions and other factors.
  • Sector Risk.    Although the Fund does not employ a sector focus, its exposure, from time to time, to specific sectors will increase based on the Adviser’s perception of available investment opportunities. If the Fund focuses on a particular sector, the Fund may face an increased risk that the value of its portfolio will decrease because of events disproportionately affecting that sector. Furthermore, investments in particular sectors may be more volatile than the broader market as a whole.
Risk Lose Money [Text] rr_RiskLoseMoney Your investment in the Fund is not guaranteed; you may lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table that follow provide an indication 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, five years, and ten years compared with those of a broad based securities market index and an additional style specific index. As with all mutual funds, the Fund’s past performance (before and after taxes) does not predict how the Fund will perform in the future. Updated information on the Fund’s results can be obtained by visiting www.gabelli.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table that follow provide an indication 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, five years, and ten years compared with those of a broad based securities market index and an additional style specific index.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.gabelli.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture As with all mutual funds, the Fund’s past performance (before and after taxes) does not predict how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading GAMCO INTERNATIONAL GROWTH FUND, INC.
(Total Returns for Class AAA Shares for the Years Ended December 31)
Bar Chart Narrative [Text Block] rr_BarChartNarrativeTextBlock chart
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock During the calendar years shown in the bar chart, the highest return for a quarter was 21.20% (quarter ended June 30, 2009) and the lowest return for a quarter was (23.60)% (quarter ended September 30, 2008).
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns
(for the years ended December 31, 2017,
with maximum sales charge, if applicable)
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 Actual after-tax returns depend on the investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax deferred arrangements, such as 401(k) plans or individual retirement accounts, including Roth IRAs and SEP IRAs (collectively, “IRAs”).
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown only for Class AAA shares. After-tax returns for other classes will vary due to the differences in expenses.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than “Return Before Taxes” because the investor is assumed to be able to use the capital loss from the sale of Fund shares to offset other taxable gains.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The returns shown for Class I shares prior to their first issuance date are those of the Class AAA shares of the Fund. All classes of the Fund would have substantially similar annual returns because the shares are invested in the same portfolio of securities and the annual returns would differ only to the extent that the classes do not have the same expenses.

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. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than “Return Before Taxes” because the investor is assumed to be able to use the capital loss from the sale of Fund shares to offset other taxable gains. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax deferred arrangements, such as 401(k) plans or individual retirement accounts, including Roth IRAs and SEP IRAs (collectively, “IRAs”). After-tax returns are shown only for Class AAA shares. After-tax returns for other classes will vary due to the differences in expenses.
GAMCO INTERNATIONAL GROWTH FUND, INC | Class AAA Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption or offering price, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (as a percentage of amount invested) rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption Fee (as a percentage of amount redeemed for shares held 7 days or less) rr_RedemptionFeeOverRedemption 2.00%
Exchange Fee rr_ExchangeFeeOverRedemption none
Management Fees rr_ManagementFeesOverAssets 1.00%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.89%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.14%
Less Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 2.14%
1 Year rr_ExpenseExampleYear01 $ 217
3 Years rr_ExpenseExampleYear03 670
5 Years rr_ExpenseExampleYear05 1,149
10 Years rr_ExpenseExampleYear10 2,472
1 Year rr_ExpenseExampleNoRedemptionYear01 217
3 Years rr_ExpenseExampleNoRedemptionYear03 670
5 Years rr_ExpenseExampleNoRedemptionYear05 1,149
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,472
2008 rr_AnnualReturn2008 (43.21%)
2009 rr_AnnualReturn2009 38.02%
2010 rr_AnnualReturn2010 19.16%
2011 rr_AnnualReturn2011 (9.95%)
2012 rr_AnnualReturn2012 17.35%
2013 rr_AnnualReturn2013 12.09%
2014 rr_AnnualReturn2014 (5.45%)
2015 rr_AnnualReturn2015 (2.94%)
2016 rr_AnnualReturn2016 (2.44%)
2017 rr_AnnualReturn2017 29.30%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.20%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (23.60%)
Past One Year rr_AverageAnnualReturnYear01 29.30%
Past Five Years rr_AverageAnnualReturnYear05 5.35%
Past Ten Years rr_AverageAnnualReturnYear10 2.51%
GAMCO INTERNATIONAL GROWTH FUND, INC | Class A Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (Load) (as a percentage of redemption or offering price, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (as a percentage of amount invested) rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption Fee (as a percentage of amount redeemed for shares held 7 days or less) rr_RedemptionFeeOverRedemption 2.00%
Exchange Fee rr_ExchangeFeeOverRedemption none
Management Fees rr_ManagementFeesOverAssets 1.00%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.89%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.14%
Less Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 2.14%
1 Year rr_ExpenseExampleYear01 $ 780
3 Years rr_ExpenseExampleYear03 1,206
5 Years rr_ExpenseExampleYear05 1,658
10 Years rr_ExpenseExampleYear10 2,905
1 Year rr_ExpenseExampleNoRedemptionYear01 780
3 Years rr_ExpenseExampleNoRedemptionYear03 1,206
5 Years rr_ExpenseExampleNoRedemptionYear05 1,658
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,905
Past One Year rr_AverageAnnualReturnYear01 21.89%
Past Five Years rr_AverageAnnualReturnYear05 4.12%
Past Ten Years rr_AverageAnnualReturnYear10 1.95%
GAMCO INTERNATIONAL GROWTH FUND, INC | Class C Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption or offering price, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (as a percentage of amount invested) rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption Fee (as a percentage of amount redeemed for shares held 7 days or less) rr_RedemptionFeeOverRedemption 2.00%
Exchange Fee rr_ExchangeFeeOverRedemption none
Management Fees rr_ManagementFeesOverAssets 1.00%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.89%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.89%
Less Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 2.89%
1 Year rr_ExpenseExampleYear01 $ 392
3 Years rr_ExpenseExampleYear03 895
5 Years rr_ExpenseExampleYear05 1,523
10 Years rr_ExpenseExampleYear10 3,214
1 Year rr_ExpenseExampleNoRedemptionYear01 292
3 Years rr_ExpenseExampleNoRedemptionYear03 895
5 Years rr_ExpenseExampleNoRedemptionYear05 1,523
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 3,214
Past One Year rr_AverageAnnualReturnYear01 27.38%
Past Five Years rr_AverageAnnualReturnYear05 4.57%
Past Ten Years rr_AverageAnnualReturnYear10 1.75%
GAMCO INTERNATIONAL GROWTH FUND, INC | Class I Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption or offering price, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (as a percentage of amount invested) rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption Fee (as a percentage of amount redeemed for shares held 7 days or less) rr_RedemptionFeeOverRedemption 2.00%
Exchange Fee rr_ExchangeFeeOverRedemption none
Management Fees rr_ManagementFeesOverAssets 1.00%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.89%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.89%
Less Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.89%) [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 1.00% [1]
1 Year rr_ExpenseExampleYear01 $ 102
3 Years rr_ExpenseExampleYear03 507
5 Years rr_ExpenseExampleYear05 938
10 Years rr_ExpenseExampleYear10 2,139
1 Year rr_ExpenseExampleNoRedemptionYear01 102
3 Years rr_ExpenseExampleNoRedemptionYear03 507
5 Years rr_ExpenseExampleNoRedemptionYear05 938
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,139
Past One Year rr_AverageAnnualReturnYear01 30.78%
Past Five Years rr_AverageAnnualReturnYear05 6.24%
Past Ten Years rr_AverageAnnualReturnYear10 3.08%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 11, 2008
GAMCO INTERNATIONAL GROWTH FUND, INC | Return After Taxes on Distributions | Class AAA Shares  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 28.05%
Past Five Years rr_AverageAnnualReturnYear05 4.74%
Past Ten Years rr_AverageAnnualReturnYear10 2.01%
GAMCO INTERNATIONAL GROWTH FUND, INC | Return After Taxes on Distributions and Sale of Fund Shares | Class AAA Shares  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 17.88%
Past Five Years rr_AverageAnnualReturnYear05 4.24%
Past Ten Years rr_AverageAnnualReturnYear10 2.08%
GAMCO INTERNATIONAL GROWTH FUND, INC | Morgan Stanley Capital International (“MSCI”) Europe, Australia, and the Far East (“EAFE”) Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 25.03%
Past Five Years rr_AverageAnnualReturnYear05 7.90%
Past Ten Years rr_AverageAnnualReturnYear10 1.94%
GAMCO INTERNATIONAL GROWTH FUND, INC | Lipper International Multi-Cap Growth Fund Classification  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 29.81%
Past Five Years rr_AverageAnnualReturnYear05 7.88%
Past Ten Years rr_AverageAnnualReturnYear10 2.14%
[1] Gabelli Funds, LLC, the Fund’s Adviser, has contractually agreed to waive all or a portion of its investment advisory fee and/or to reimburse certain expenses of the Fund to the extent necessary to maintain the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement (excluding brokerage, acquired fund fees and expenses, interest, taxes, and extraordinary expenses) for Class I shares at no more than 1.00%. The fee waiver and expense reimbursement arrangement will continue until at least April 30, 2019, and may not be terminated by the Adviser before such date. The Fund will carry forward, for a period not to exceed three years from the date that an amount is waived, any fees in excess of the expense limitation and repay the Adviser such amount provided the Fund is able to do so without exceeding the lesser of (1) the expense limit in effect at the time of the waiver or reimbursement, as applicable, or (2) the expense limit in effect at the time of recoupment.