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Alger SMid Cap Growth Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] ck0000003521_SupplementTextBlock

THE ALGER FUNDS


Alger SMid Cap Growth Fund


Supplement dated July 5, 2017 to Current Institutional Prospectus


The following replaces the information under the headings noted on page 21 of the Prospectus:
Risk/Return [Heading] rr_RiskReturnHeading Alger SMid Cap Growth Fund
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)
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent The expense information in the table has been restated to reflect current fees.
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 $10,000.00 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:
Alger SMid Cap Growth Fund | Alger SMid Cap Growth Fund Class I  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fees rr_ManagementFeesOverAssets 0.81% [1]
Distribution and/or Shareholder Servicing (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25% [1]
Other Expenses rr_OtherExpensesOverAssets 0.41% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.47% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 150
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 465
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 803
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,757
[1] The expense information in the table has been restated to reflect current fees.