Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Mar. 01, 2021
Class A C Shares | Alger Health Sciences 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;margin-left:0%;text-transform:uppercase;">Alger Health Sciences Fund</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Alger Health Sciences Fund seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">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. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and examples below.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” on page 53 and in Appendix A – Waivers and Discounts Available from Intermediaries on page A-1 in the Fund’s Prospectus, and in the sections “Right of Accumulation (Class A Shares)” and “Letter of Intent (Class A Shares)” on page 29 of the Fund’s Statement of Additional Information.
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;">(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;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">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 examples, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 131.29% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	131.29%
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	<span style="color:#262626;font-family:Arial;font-size:9pt;">You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least </span><span style="color:#262626;font-family:Arial;font-size:9pt;">$25,000</span><span style="color:#262626;font-family:Arial;font-size:9pt;"> in Class A Shares of the Alger Family of Funds, including the Fund.</span>
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 25,000
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#0065D2;font-family:Arial;font-size:9pt;font-weight:bold;margin-left:0%;">Example</span>
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 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. 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	<span style="color:#262626;font-family:Arial;font-size:8pt;font-weight:bold;">You would pay the following expenses if you did not redeem your shares:</span>
Strategy [Heading]	rr_StrategyHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Principal Investment Strategy</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Fred Alger Management, LLC (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.Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies of any market capitalization that are engaged in the health sciences sector. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges. A company will be considered to be engaged in the health sciences sector if it derives at least 50% of its earnings or revenues from, or devotes at least 50% of its assets to, activities in any area of the health sciences sector, including health care services, pharmaceuticals, medical equipment and supplies and applied research and development. Such companies include, but are not limited to:•hospitals, clinical test laboratories, convalescent and mental health care facilities, home care providers, and companies that supply services to any of the foregoing;•companies involved in pharmaceuticals, biotechnology, biochemistry and diagnostics; and•producers and manufacturers of medical, dental and optical supplies and equipment.The Fund 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.The Fund can also invest in privately placed securities, which are securities acquired in non-public offerings for which there is no readily available market.The Fund can invest in foreign securities.
Risk [Heading]	rr_RiskHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">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 war, acts of terrorism, the spread of infectious illness or other public health issues, recessions, or other events could have a significant impact on the Fund and its investments.An outbreak of respiratory disease caused by a novel coronavirus designated as COVID-19 was first detected in China in December 2019 and subsequently spread internationally. The transmission of COVID-19 and efforts to contain its spread have resulted in, among other things, border closings and other significant travel restrictions and disruptions; significant disruptions to business operations, supply chains and customer activity; lower consumer demand for goods and services; significant job losses and increasing unemployment; event cancellations and restrictions; service cancellations, reductions and other changes; significant challenges in healthcare service preparation and delivery; prolonged quarantines; as well as general concern and uncertainty that has negatively affected the economic environment. The impact of this outbreak and any other epidemic or pandemic that may arise in the future could adversely affect the economies of many nations or the entire global economy and the financial performance of individual issuers, sectors, industries, asset classes, and markets in significant and unforeseen ways. Although the Federal Reserve has taken a number of actions to mitigate the impact of COVID-19 on U.S. markets and institutions, including decreasing interest rates and implementing a variety of emergency stimulus measures, these actions may not succeed or have the intended effect. This crisis or other public health crises may also exacerbate other pre-existing political, social, economic, market and financial risks. The duration of the COVID-19 outbreak and its effects cannot be determined with certainty. The foregoing could result in significant market volatility, exchange trading suspensions and closures, declines in global financial markets, higher default rates and a substantial economic downturn or recession. Such impacts could impair the Fund’s ability to maintain operational standards (such as with respect to satisfying redemption requests), disrupt the operations of the Fund’s service providers, adversely affect the value and liquidity of the Fund’s investments and negatively impact the Fund’s performance and your investment in the Fund.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.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 because of the potentially less frequent trading of stocks of smaller market capitalization.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.•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.Privately Placed Securities Risk – A private placement is an offering of a company’s securities that is not registered with the Securities and Exchange Commission (the “SEC”) and is not offered to the public. Less information may be available about companies that make private placements than about publicly offered companies and such companies may not be subject to the disclosure and other investor protection requirements that would be applicable if their securities were publicly traded. The sale or transfer of privately placed securities may be limited or prohibited by contract or law and such investments are generally considered to be illiquid. Privately placed securities are generally fair valued as they are not traded frequently. The Fund may be required to hold such positions for several years, if not longer, regardless of valuation, which may cause the Fund to be less liquid.Foreign Securities Risk – The Fund’s performance will be influenced by political, social and economic factors affecting investments in foreign companies. Special risks associated with investments in foreign companies include exposure to currency fluctuations, lack of liquidity, potential for market manipulation, less developed or less efficient trading markets, limited access to reliable capital, lack of comprehensive company information, political instability, differing audit, regulatory, and legal standards and lack of financial reporting standards.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	<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 </span><span style="color:#262626;font-family:Arial;font-size:9pt;">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;margin-left:0%;">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.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.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.The Fund compares its performance to the S&P 500 Index, a broad based measure of market performance. The Fund also compares its performance to the Russell 3000 Health Care Index (the “Health Care Index”). The Health Care Index provides a more complete comparison of Fund performance relative to companies involved in the medical services or health care field.
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 </span><span style="color:#262626;font-family:Arial;font-size:9pt;">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;margin-left:0%;">Annual Total Return for Class A Shares</span><span style="color:#262626;font-family:Arial;font-size:10pt;font-style:italic;"> as of December 31 (%)</span>
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	<span style="color:#262626;font-family:Arial;font-size:9pt;">Performance in the bar chart does not reflect the effect </span><span style="color:#262626;font-family:Arial;font-size:9pt;">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.</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:Q2 202024.45%Worst Quarter:Q4 2018-18.72%
Performance Table Heading	rr_PerformanceTableHeading	<span style="color:#0065D2;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Average Annual Total Return as of December 31, 2020</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 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:#262626;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 One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	<span style="color:#262626;font-family:Arial;font-size:9pt;">After-tax returns for Class C Shares, which are not shown, </span><span style="color:#262626;font-family:Arial;font-size:9pt;">will vary from those shown for Class A Shares.</span>
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	<span style="color:#262626;font-family:Arial;font-size:9pt;">A “Return After Taxes on Distributions and Sale of Fund Shares” may sometimes be </span><span style="color:#262626;font-family:Arial;font-size:9pt;">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.After-tax returns for Class 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.
Class A C Shares | Alger Health Sciences Fund - AC | Class A
Risk Return Abstract	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_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Advisory Fees	rr_ManagementFeesOverAssets	0.55%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.24%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.04%
1 Year	rr_ExpenseExampleYear01	$ 625
3 Years	rr_ExpenseExampleYear03	839
5 Years	rr_ExpenseExampleYear05	1,069
10 Years	rr_ExpenseExampleYear10	$ 1,729
2011	rr_AnnualReturn2011	10.60%
2012	rr_AnnualReturn2012	11.38%
2013	rr_AnnualReturn2013	35.59%
2014	rr_AnnualReturn2014	21.99%
2015	rr_AnnualReturn2015	2.35%
2016	rr_AnnualReturn2016	(3.31%)
2017	rr_AnnualReturn2017	37.16%
2018	rr_AnnualReturn2018	5.79%
2019	rr_AnnualReturn2019	22.03%
2020	rr_AnnualReturn2020	30.98%
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	24.45%
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	(18.72%)
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 2002
Class A C Shares | Alger Health Sciences Fund - AC | Class C
Risk Return Abstract	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_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Advisory Fees	rr_ManagementFeesOverAssets	0.55%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.26%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.81%
1 Year	rr_ExpenseExampleYear01	$ 284
3 Years	rr_ExpenseExampleYear03	569
5 Years	rr_ExpenseExampleYear05	980
10 Years	rr_ExpenseExampleYear10	2,127
1 Year	rr_ExpenseExampleNoRedemptionYear01	184
3 Years	rr_ExpenseExampleNoRedemptionYear03	569
5 Years	rr_ExpenseExampleNoRedemptionYear05	980
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,127
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 2002
Class A C Shares | Alger Health Sciences Fund - AC | Return Before Taxes | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	24.10%
5 Years	rr_AverageAnnualReturnYear05	16.26%
10 Years	rr_AverageAnnualReturnYear10	16.05%
Class A C Shares | Alger Health Sciences Fund - AC | Return Before Taxes | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	29.02%
5 Years	rr_AverageAnnualReturnYear05	16.63%
10 Years	rr_AverageAnnualReturnYear10	15.79%
Class A C Shares | Alger Health Sciences Fund - AC | Return After Taxes on Distributions | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	20.57%
5 Years	rr_AverageAnnualReturnYear05	14.63%
10 Years	rr_AverageAnnualReturnYear10	13.32%
Class A C Shares | Alger Health Sciences Fund - AC | Return After Taxes on Distributions and Sale of Fund Shares | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	16.05%
5 Years	rr_AverageAnnualReturnYear05	12.79%
10 Years	rr_AverageAnnualReturnYear10	12.38%
Class A C Shares | Alger Health Sciences Fund - AC | S&P 500 Index (reflects no deductions for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	18.40%
5 Years	rr_AverageAnnualReturnYear05	15.22%
10 Years	rr_AverageAnnualReturnYear10	13.88%
Class A C Shares | Alger Health Sciences Fund - AC | Russell 3000 Health Care TR (USD) (reflects no deductions for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	19.34%
5 Years	rr_AverageAnnualReturnYear05	12.87%
10 Years	rr_AverageAnnualReturnYear10	16.63%

[1] 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.