Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	THE ALGER FUNDS
Prospectus Date	rr_ProspectusDate	Mar. 01, 2022
Class Y Shares | Alger Small Cap Focus Fund - AC
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<span style="color:#262626;font-family:Arial;font-size:10pt;font-weight:bold;text-transform:uppercase;">Alger Small Cap Focus Fund</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Alger Small Cap Focus Fund seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Fund Fees and Expenses</span>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	<span style="color:#262626;font-family:Arial;font-size:9pt;font-weight:bold;">Shareholder Fees</span> <br/><span style="color:#262626;font-family:Arial;font-size:9pt;margin-left:0%;">(fees paid directly from your investment)</span>
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<span style="color:#262626;font-family:Arial;font-size:9pt;font-weight:bold;">Annual Fund Operating Expenses</span> <br/><span style="color:#262626;font-family:Arial;font-size:9pt;margin-left:0%;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	<span style="color:#262626;font-family:Arial;font-size:8pt;">February </span><span style="color:#262626;font-family:Arial;font-size:8pt;">29, 2024</span>
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Portfolio Turnover</span>
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 56.71% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	56.71%
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#0065D2;font-family:Arial;font-size:9pt;font-weight:bold;">Example</span>
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 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. 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	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Investment Strategy</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Manager 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, rapidly growing demand or market dominance. Positive Lifecycle Change companies are, for example, companies benefitting from new regulations, a new product innovation or new management.The Fund normally invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies that, at the time of purchase of the securities, have total market capitalization between (1) the higher of (a) $5 billion or (b) the company in either the Russell 2000 Growth Index or the MSCI USA Small Cap Index (each, an “Index” and together, the “Indexes”) with the highest capitalization, and (2) the company in either Index with the lowest capitalization, at any time during the most recent 12-month period as reported by either Index. Both Indexes are broad-based indexes of small capitalization stocks. At December 31, 2021, the market capitalization of the companies in the Indexes ranged from $31 million to $33 billion. Because of the Fund’s long-term approach to investing, it could have a significant portion of its assets invested in securities of issuers that have appreciated beyond the market capitalization thresholds noted. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges.In addition, under normal market conditions, the Fund invests at least 25% of its total assets in technology companies focused in the fields of medicine and information. From time to time, the Fund may have 25% or more of its total assets invested in any one of these industries. The Manager believes that there is very little in the field of medicine that does not use some type of medical technology and that has not been affected by new technology. Advances in technology increasingly pervade health care companies through changes in medical and surgical procedures, drugs, medical devices, and new support systems.As a focus fund, the Fund intends to invest a substantial portion of its assets in a smaller number of issuers. Generally the Fund will own approximately 50 holdings. Fund holdings may occasionally differ from this number for a variety of reasons, including, among others, because of extreme market volatility, such as when the Fund has entered a temporary defensive position.  Additionally, the Fund may temporarily exceed the stated number of holdings when it acquires a new holding and determines that it is in the best interests of shareholders to sell an existing holding over a period of time, instead of immediately selling the entire holding.The Fund may sell a stock when it reaches a target price, it fails to perform as expected, or other opportunities appear more attractive.The Fund invests in cash (and cash equivalents) when the Fund is unable to find enough attractive long-term investments to meet its investment objective, to meet redemptions and/or when the Manager believes it is advisable to do so during times of short-term market volatility. During these times, cash (and cash equivalents) will not exceed 15% of the Fund’s assets.
Risk [Heading]	rr_RiskHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Risks</span>
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. The following is a summary description of principal risks involved in investing in the Fund.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. Local, regional or global events such as environmental or natural disasters, war, terrorism, pandemics, outbreaks of infectious diseases, and similar public health threats, recessions, or other events could have a significant impact on the Fund and its investments.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.Small Cap Securities Risk – There may be greater risk in investing in companies with small market capitalizations rather than larger, more established companies owing to such factors as more limited product lines or financial resources or lack of management depth. It may also be difficult or impossible to liquidate a security position at a time and price acceptable to the Fund because of the potentially less frequent trading of stocks of smaller market capitalization.Small Number of Holdings Risk – Under normal circumstances, the Fund invests in a small number of issuers. Therefore, the Fund’s performance may be more vulnerable to changes in the market value of a single issuer and more susceptible to risks associated with a single economic, political, or regulatory occurrence than a fund that has a higher number of holdings.Concentration Risk – By focusing on an industry or a group of industries, the Fund carries much greater risks of adverse developments and price movements in such industries than a fund that invests in a wider variety of industries. Because the Fund concentrates in a specific industry or group of industries, there is also the risk that the Fund will perform poorly during a slump in demand for securities of companies in such industries.•Technology Companies Risk – The Fund may have a significant portion of its assets invested in securities of technology-related companies. Therefore, the Fund may be more susceptible to particular risks that may affect companies in the information technology sector and technology-related sectors than if it were invested in a wider variety of companies in unrelated sectors. At times, the performance of such companies will lag the performance of other industries or the broader market as a whole. Certain technology related companies may face special risks that their products or services may not prove to be commercially successful. Technology related companies are also strongly affected by worldwide scientific or technological developments. As a result, their products may rapidly become obsolete. Such companies are also often subject to governmental regulation and may, therefore, be adversely affected by governmental policies. These factors may lead to limited earnings and/or failing profit margins. As a result, the value of technology related companies’ securities may fall or fail to rise. Many technology related companies’ securities have historically been more volatile than other securities, especially over the short term.•Healthcare Companies Risk – The Fund may have a significant portion of its assets invested in securities of healthcare companies. At times, the performance of healthcare companies will lag the performance of other industries or the broader market as a whole, and the performance of such companies may be more volatile. Healthcare companies may also be significantly affected by intense competition, aggressive pricing, government regulation, technological innovations, product obsolescence, patent considerations, product compatibility and consumer preferences.Cash Position Risk – At times, the Fund may hold a large cash position, which may underperform relative to equity securities.
Risk Lose Money [Text]	rr_RiskLoseMoney	<span style="color:#262626;font-family:Arial;font-size:9pt;">The Fund’s share price may go down, which means you could lose money.</span>
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	<span style="color:#262626;font-family:Arial;font-size:9pt;"> 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.</span>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Performance</span>
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. 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	<span style="color:#262626;font-family:Arial;font-size:9pt;">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.</span>
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	<span style="color:#262626;font-family:Arial;font-size:9pt;">www.alger.com</span>
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<span style="color:#262626;font-family:Arial;font-size:9pt;"> The Fund’s past performance (before and after taxes) is not necessarily an indication of how it will perform in the future.</span>
Bar Chart [Heading]	rr_BarChartHeading	<span style="color:#262626;font-family:Arial;font-size:10pt;font-weight:bold;">Annual Total Return for Class Y Shares</span><span style="color:#262626;font-family:Arial;font-size:10pt;line-height:12pt;"> </span><span style="color:#262626;font-family:Arial;font-size:10pt;font-style:italic;"> as of December 31 (%)</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:Q2 202036.88%Worst Quarter:Q4 2018-21.13%
Performance Table Heading	rr_PerformanceTableHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;">Average Annual Total Return as of December 31, 2021</span>
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	<span style="color:#262626;font-family:Arial;font-size:9pt;">after-tax returns are calculated using the historical highest individual federal marginal income tax rates and </span><span style="color:#262626;font-family:Arial;font-size:9pt;">do not reflect the impact of state and local taxes.</span>
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	<span style="color:#262626;font-family:Arial;font-size:9pt;"> Actual after-tax returns depend on an investor’s tax situation and may differ from </span><span style="color:#000000;font-family:Arial;font-size:9pt;">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.</span>
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	<span style="color:#000000;font-family:Arial;font-size:9pt;"> 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.</span>
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	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 when there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.
Class Y Shares | Alger Small Cap Focus Fund - AC | Class Y
Risk Return Abstract	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Advisory Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.08%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.83%	[1]
1 Year	rr_ExpenseExampleYear01	$ 85
3 Years	rr_ExpenseExampleYear03	265
5 Years	rr_ExpenseExampleYear05	460
10 Years	rr_ExpenseExampleYear10	$ 1,025
2018	rr_AnnualReturn2018	14.51%
2019	rr_AnnualReturn2019	24.59%
2020	rr_AnnualReturn2020	53.75%
2021	rr_AnnualReturn2021	(13.95%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<span style="color:#262626;font-family:Arial;font-size:8pt;font-weight:bold;">Best Quarter:</span>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	36.88%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<span style="color:#262626;font-family:Arial;font-size:8pt;font-weight:bold;">Worst Quarter:</span>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.13%)
Inception Date	rr_AverageAnnualReturnInceptionDate	Feb. 28, 2017
Class Y Shares | Alger Small Cap Focus Fund - AC | Return Before Taxes | Class Y
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(13.95%)
Since Inception	rr_AverageAnnualReturnSinceInception	18.71%
Class Y Shares | Alger Small Cap Focus Fund - AC | Return After Taxes on Distributions | Class Y
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(15.27%)
Since Inception	rr_AverageAnnualReturnSinceInception	18.03%
Class Y Shares | Alger Small Cap Focus Fund - AC | Return After Taxes on Distributions and Sale of Shares | Class Y
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.34%)
Since Inception	rr_AverageAnnualReturnSinceInception	15.10%
Class Y Shares | Alger Small Cap Focus Fund - AC | Russell 2000 Growth Index (reflects no deductions for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	2.83%
Since Inception	rr_AverageAnnualReturnSinceInception	14.10%

[1] Fred Alger Management, LLC (the “Manager”) has contractually agreed to waive fees or to reimburse Fund expenses (excluding acquired fund fees and expenses, dividend expense on short sales, borrowing costs, interest, taxes, brokerage and extraordinary expenses, to the extent applicable) through February 29, 2024 to the extent necessary to limit the total annual fund operating expenses of the Class Y Shares of the Fund to .85% of the class’s average daily net assets. This expense reimbursement may only be amended or terminated prior to its expiration date by agreement between the Manager and the Fund’s Board of Trustees, and will terminate automatically in the event of termination of the Investment Advisory Agreement. The Manager may, during the term of the contract, recoup any fees waived or expenses reimbursed pursuant to the contract; however, the Fund will only make repayments to the Manager if such repayment does not cause the Fund’s expense ratio after the repayment is taken into account, to exceed both (i) the expense cap in place at the time such amounts were waived or reimbursed, and (ii) the Fund’s current expense cap. Such recoupment is limited to two years from the date the amount is initially waived or reimbursed.