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Class I 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.
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 Feb. 28, 2017
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 example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 114.81% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 114.81%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The following 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, 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 whether or not you redeemed your shares at the end of each period:
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 principal trading market is 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.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

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.


Investment Style 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.


The following risks may also apply:


•  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.


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.
Risk Lose Money [Text] rr_RiskLoseMoney 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.
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. Remember that 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 Remember that 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 I Shares as of December 31 (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter:
Q3 2013 8.67% 		  Worst Quarter:
Q3 2014 -4.24% 		 
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 8.67%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2014
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (4.24%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction 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 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 where 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. A "Return After Taxes on Distributions and Sale of Fund Shares" may sometimes be higher than the other two return figures; this happens where 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, 2015
Class I Prospectus | Alger International Growth Fund | MSCI ACWI ex USA (reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (5.25%)
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 0.42%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate May 31, 2013
Class I Prospectus | Alger International Growth Fund | Alger International Growth Fund Class I  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_MaximumAccountFeeOverAssets none
Management Fees rr_ManagementFeesOverAssets 0.71%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.34%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.30%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.15%) [1]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 1.15%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 117
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 397
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 699
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,555
Annual Return 2014 rr_AnnualReturn2014 (3.24%)
Annual Return 2015 rr_AnnualReturn2015 1.13%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 1.13%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.17%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate May 31, 2013
Class I Prospectus | Alger International Growth Fund | Alger International Growth Fund Class I | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.98%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 3.83%
Class I Prospectus | Alger International Growth Fund | Alger International Growth Fund Class I | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.64%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 3.04%
[1] Fred Alger Management, Inc. has contractually agreed to reimburse Fund expenses (excluding interest, taxes, brokerage, and extraordinary expenses) through February 28, 2017 to the extent necessary to limit the total annual fund operating expenses of the Class I Shares of the Fund to 1.15% of the class's average daily net assets. This expense reimbursement cannot be terminated. Fred Alger Management, Inc. may recoup reimbursed expenses during the one-year term of the expense reimbursement contract if the expense ratio falls below the stated limitation at the time of the reimbursement.