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Class A, B, & C Prospectus | Alger International Growth Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Alger International Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Alger International Growth Fund seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fund Fees and Expenses
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 $25,000 in Class A Shares of the Alger Family of Funds, including the Fund. More information about these and other discounts is available from your financial professional and in "Purchasing and Redeeming Fund Shares" and in Appendix A – Waivers and Discounts Available from Intermediaries in the Fund's Prospectus, and in the sections "Right of Accumulation (Class A Shares)" and "Letter of Intent (Class A Shares)" in the Fund's Statement of Additional Information.
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 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 annual fund operating expenses or in the examples, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 148.35% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 148.35%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The following examples are intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The examples assume that you invest $10,000 in the Fund for the time periods indicated, that your investment has a 5% return each year and that the Fund's operating expenses remain the same.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption Although your actual costs may be higher or lower, based on these assumptions you would pay the following expenses if you redeemed your shares at the end of each period:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Fred Alger Management, Inc. believes companies undergoing Positive Dynamic Change offer the best investment opportunities. Positive Dynamic Change refers to companies realizing High Unit Volume Growth or companies undergoing Positive Lifecycle Change. High Unit Volume Growth companies are traditional growth companies experiencing, for example, significantly growing demand or market dominance. Positive Lifecycle Change companies are, for example, companies benefitting from regulatory change, a new product introduction or management change.


Under normal circumstances, the Fund invests at least 80% of its net assets in equity securities, including common stocks, American Depositary Receipts and Global Depositary Receipts, of foreign companies. Foreign companies are companies (i) that are organized under the laws of a foreign country; (ii) whose securities are primarily listed in a foreign country; or (iii) that have a majority of their assets, or derive more than 50% of their revenue or profits from businesses, investments, or sales, outside the U.S. The Fund normally focuses its foreign investments in developed countries, but may also invest in emerging market securities. The Fund may invest in companies of any market capitalization, from large, well-established companies to small, emerging growth companies.


The Fund generally invests in at least three foreign countries, and, at times, may invest a substantial portion of its assets in a single foreign country. The Fund's benchmark is the Morgan Stanley Capital International (MSCI) All Country World Index (ACWI) ex USA, which is an unmanaged market capitalization-weighted index designed to provide a broad measure of equity market performance throughout the world, including both developed and emerging markets, but excluding the United States. The Fund may also compare its performance to the MSCI Europe, Australasia, and Far East (EAFE) Index, which is an unmanaged, market capitalization-weighted index designed to measure the performance of publicly traded stocks issued by companies in developed markets, excluding the United States and Canada. While the MSCI EAFE Index excludes stocks of Canadian companies, the Fund may invest in such stocks.


The Fund's portfolio manager(s) may sell a stock when it reaches a target price, it fails to perform as expected, or other opportunities appear more attractive. As a result, the Fund may engage in active trading of portfolio securities.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund involves risks. The Fund's share price may go down, which means you could lose money. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.


Investment Risk — An investment in the Fund is subject to investment risk, including the possible loss of the entire principal amount that you invest.


Market Risk — Your investment in Fund shares represents an indirect investment in the securities owned by the Fund. The value of these securities, like other investments, may move up or down, sometimes rapidly and unpredictably. Your Fund shares at any point in time may be worth less than what you invested, even after taking into account the reinvestment of Fund dividends and distributions.


Equity Securities Risk – As with any fund that invests in stocks, your investment will fluctuate in value, and the loss of your investment is a risk of investing. The Fund's price per share will fluctuate due to changes in the market prices of its investments. Also, the Fund's investments may not grow as fast as the rate of inflation and stocks tend to be more volatile than some other investments you could make, such as bonds.


Growth Stocks Risk – Prices of growth stocks tend to be higher in relation to their companies' earnings and may be more sensitive to market, political and economic developments than other stocks, making their prices more volatile. An investment in the Fund may be better suited to investors who seek long-term capital growth and can tolerate fluctuations in their investment's value.


Foreign Securities Risk – The Fund's performance will be influenced by political, social and economic factors affecting investments in foreign issuers, particularly emerging country issuers. Special risks associated with investments in emerging country issuers include exposure to currency fluctuations, less liquidity, less developed or less efficient trading markets, lack of comprehensive company information, political instability and differing auditing and legal standards. The securities of issuers located in emerging markets can be more volatile, and less liquid, than those of issuers in more mature economies.


Smaller Cap Securities Risk – Investing in companies of all capitalizations involves the risk that smaller issuers in which the Fund invests may have limited product lines or financial resources, or lack management depth. It may also be difficult or impossible to liquidate a security position at a time and price acceptable to the Fund owing to the potentially less frequent trading of stocks of smaller market capitalization.


Portfolio Turnover (Active Trading) Risk – Because the Fund may engage in active trading of portfolio securities, it may incur increased transaction costs and brokerage commissions, both of which can lower the actual return on an investment. Active trading may also increase short-term gains and losses, which may affect the taxes a shareholder has to pay.
Risk Lose Money [Text] rr_RiskLoseMoney The Fund's share price may go down, which means you could lose money.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following bar chart and the table beneath it provide some 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 the indicated periods compare with those of an appropriate benchmark of market performance. Performance in the bar chart does not reflect the effect of the sales charge imposed on purchases of Class A Shares of the Fund. If the bar chart reflected the applicable sales charges, returns would be less than those shown. Previously, the Fund followed different investment strategies under the name "Alger Large Cap Growth Fund" and was managed by a different portfolio manager. Performance prior to May 31, 2013 reflects that prior management style and does not reflect the Fund's current investment strategies and investment personnel. The Fund's past performance (before and after taxes) is not necessarily an indication of how it will perform in the future. Updated performance information is available on the Fund's website www.alger.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and the table beneath it provide some 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 the indicated periods compare with those of an appropriate benchmark of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.alger.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance (before and after taxes) is not necessarily an indication of how it will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Return for Class A Shares as of December 31 (%)
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Performance in the bar chart does not reflect the effect of the sales charge imposed on purchases of Class A Shares of the Fund. If the bar chart reflected the applicable sales charges, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter:
Q2 2009 15.77% 		  Worst Quarter:
Q4 2008 -26.33% 		 
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.77%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.33%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deductions for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate In the foregoing table, 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 The after-tax returns shown may not be relevant to investors who hold their Fund 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 After-tax returns for Class B and C Shares, which are not shown, will vary from those shown for Class A Shares.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher A "Return After Taxes on Distributions and Sale of Fund Shares" may sometimes be higher than the other two return figures; this happens when there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

In the foregoing table, 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. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. The after-tax returns shown may not be relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns for Class B and C Shares, which are not shown, will vary from those shown for Class A Shares. A "Return After Taxes on Distributions and Sale of Fund Shares" may sometimes be higher than the other two return figures; this happens when there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.
Caption rr_AverageAnnualReturnCaption Average Annual Total Return as of December 31, 2017
Class A, B, & C Prospectus | Alger International Growth Fund | MSCI ACWI ex USA (reflects no deductions for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 27.77%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 7.28%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 2.31%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.93% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 1996
Class A, B, & C Prospectus | Alger International Growth Fund | Alger International Growth Fund Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases as a % of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.25%
Maximum deferred sales charge (load) as a % of purchase price or redemption proceeds, whichever is lower rr_MaximumDeferredSalesChargeOverOther none [2]
Management Fees rr_ManagementFeesOverAssets 0.71%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.38%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.34%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock Purchases of $1 million or more of Class A Shares at net asset value may be subject to a contingent deferred sales charge of 1.00% on redemptions made within 12 months of purchase.
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 $25,000 in Class A Shares of the Alger Family of Funds, including the Fund.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 25,000
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 654
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 927
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,221
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,053
Annual Return 2008 rr_AnnualReturn2008 (45.83%)
Annual Return 2009 rr_AnnualReturn2009 40.97%
Annual Return 2010 rr_AnnualReturn2010 12.67%
Annual Return 2011 rr_AnnualReturn2011 (0.51%)
Annual Return 2012 rr_AnnualReturn2012 9.31%
Annual Return 2013 rr_AnnualReturn2013 23.94%
Annual Return 2014 rr_AnnualReturn2014 (3.41%)
Annual Return 2015 rr_AnnualReturn2015 0.97%
Annual Return 2016 rr_AnnualReturn2016 (5.50%)
Annual Return 2017 rr_AnnualReturn2017 26.70%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 20.01%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.51%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 2.53%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.49% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 1996
Class A, B, & C Prospectus | Alger International Growth Fund | Alger International Growth Fund Class A | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 17.39%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.79%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 2.14%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.68% [1]
Class A, B, & C Prospectus | Alger International Growth Fund | Alger International Growth Fund Class A | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.29%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.74%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 1.78%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.24% [1]
Class A, B, & C Prospectus | Alger International Growth Fund | Alger International Growth Fund Class B  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases as a % of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) as a % of purchase price or redemption proceeds, whichever is lower rr_MaximumDeferredSalesChargeOverOther 5.00%
Management Fees rr_ManagementFeesOverAssets 0.71%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.34%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.05%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 708
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 943
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,303
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,197
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 208
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 643
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,103
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,197
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 20.80%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.60%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 2.51%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.46% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Nov. 11, 1986
Class A, B, & C Prospectus | Alger International Growth Fund | Alger International Growth Fund Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases as a % of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) as a % of purchase price or redemption proceeds, whichever is lower rr_MaximumDeferredSalesChargeOverOther 1.00%
Management Fees rr_ManagementFeesOverAssets 0.71%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.42%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.13%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 316
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 667
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,144
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,462
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 216
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 667
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,144
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,462
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 24.69%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.84%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 2.28%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.29% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jul. 31, 1997
[1] Performance of the Fund's Class C Shares prior to July 31, 1997 reflects the performance of the Fund's Class A Shares, as adjusted with currently applicable sales charges and operating expenses, which differ from historical charges and expenses. Since inception performance of the Fund's Class B Shares is available upon request.
[2] Purchases of $1 million or more of Class A Shares at net asset value may be subject to a contingent deferred sales charge of 1.00% on redemptions made within 12 months of purchase.