Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	ALGER FUNDS
Prospectus Date	rr_ProspectusDate	Mar. 01, 2019
Class A, C Shares | Alger Growth & Income Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<b>ALGER GROWTH & INCOME FUND</b>
Objective [Heading]	rr_ObjectiveHeading	<b>Investment Objective</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Alger Growth & Income Fund seeks to provide capital appreciation and current income.
Expense [Heading]	rr_ExpenseHeading	<b>Fund Fees and Expenses</b>
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” on page 67 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 25 of the Fund’s Statement of Additional Information.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	<b>Shareholder Fees<br/></b>(fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<b>Annual Fund Operating Expenses<br/></b>(expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<b>Portfolio Turnover</b>
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 11.05% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	11.05%
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
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	The expense information in the table has been restated to reflect a reduction in advisory fees that was effective on January 1, 2018.
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>Example</b>
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. 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	<b>You would pay the following expenses if you did not redeem your shares: </b>
Strategy [Heading]	rr_StrategyHeading	<b>Principal Investment Strategy</b>
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, 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 invests primarily in equity securities such as common or preferred stocks which Fred Alger Management, Inc. believes offer opportunities for capital appreciation and which also pay dividends. In considering such companies, Fred Alger Management, Inc. classifies them into three categories: Dividend Leaders – companies that generate high dividend yields; Dividend Growers – companies that have a history of strong and consistent dividend growth; and Kings of Cash Flow – companies that have strong potential for generating capital appreciation and the ability to return significant amounts of cash to investors as a result of their free cash flow. The Fund intends to invest at least 65% of its total assets in dividend paying equity securities. The Fund may invest up to 35% of its total assets in equity securities that do not pay dividends or in money market instruments and repurchase agreements. The Fund focuses on growing companies that, at the time of purchase of the securities, have a market capitalization equal to or greater than the market capitalization of companies included in the S&P 500 Index, as reported by the index as of the most recent quarter-end. This index is designed to track the performance of large-capitalization stocks. At December 31, 2018, the market capitalization of the companies in this index ranged from $2.31 billion to $785.03 billion. The Fund may invest a significant portion of its assets in securities of companies conducting business within a single sector, including the information technology, consumer discretionary, financials, healthcare, and industrials sectors. 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.
Risk [Heading]	rr_RiskHeading	<b>Principal Risks</b>
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. In addition, there are special risks associated with investing in preferred securities, including deferral and omission of distributions, subordination to bonds and other debt securities in a company’s capital structure, limited liquidity, limited voting rights and special redemption rights. The market value of preferred stocks is generally more sensitive to changes in interest rates than the market value of common stocks. 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. Income-Producing Securities Risk – Companies may cut or fail to declare dividends due to market downturns or other reasons. Income producing securities may become generally less favored by market participants, potentially leading such securities to underperform the broader stock market, Sector Risk – The Fund may have a significant portion of its assets invested in securities of companies conducting business within a single sector. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that sector than a fund that has a more diversified portfolio. Generally, the more broadly the Fund invests, the more it spreads risk and potentially reduces the risks of loss and volatility. Technology Companies Risk – The Fund may have a significant portion of its assets invested in securities of technology companies. Many technology companies have limited operating histories and prices of these companies’ securities have historically been more volatile than other securities, especially over the short term. Technology companies may also face increased competition, government regulation, and risk of obsolescence due to progress in technological developments. 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.
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	<b>Performance</b>
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 a different investment objective and different strategies under the name “Alger Balanced Fund.” Performance prior to April 1, 2011 does not reflect the Fund’s current investment objective and strategies. 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	<b>Annual Total Return for Class A Shares</b> 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: Q4 2011 12.46%               Worst Quarter: Q4 2018 -11.48%
Performance Table Heading	rr_PerformanceTableHeading	<b>Average Annual Total Return as of December 31, 2018</b>
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	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	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.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns for Class 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 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 Growth & Income 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	[1]
Advisory Fees	rr_ManagementFeesOverAssets	0.51%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.30%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.06%	[2]
1 Year	rr_ExpenseExampleYear01	$ 627
3 Years	rr_ExpenseExampleYear03	845
5 Years	rr_ExpenseExampleYear05	1,079
10 Years	rr_ExpenseExampleYear10	$ 1,751
2009	rr_AnnualReturn2009	28.45%
2010	rr_AnnualReturn2010	9.57%
2011	rr_AnnualReturn2011	4.83%
2012	rr_AnnualReturn2012	11.78%
2013	rr_AnnualReturn2013	29.30%
2014	rr_AnnualReturn2014	12.18%
2015	rr_AnnualReturn2015	1.17%
2016	rr_AnnualReturn2016	10.23%
2017	rr_AnnualReturn2017	20.64%
2018	rr_AnnualReturn2018	(4.72%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<b>Best Quarter:</b>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2011
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	12.46%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<b> Worst Quarter:</b>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(11.48%)
1 Year	rr_AverageAnnualReturnYear01	(9.73%)
5 Years	rr_AverageAnnualReturnYear05	6.38%
10 Years	rr_AverageAnnualReturnYear10	11.25%
Since	rr_AverageAnnualReturnSinceInception	7.64%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1996
Class A, C Shares | Alger Growth & Income 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%
Advisory Fees	rr_ManagementFeesOverAssets	0.51%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.31%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.82%	[2]
1 Year	rr_ExpenseExampleYear01	$ 285
3 Years	rr_ExpenseExampleYear03	573
5 Years	rr_ExpenseExampleYear05	985
10 Years	rr_ExpenseExampleYear10	2,137
1 Year	rr_ExpenseExampleNoRedemptionYear01	185
3 Years	rr_ExpenseExampleNoRedemptionYear03	573
5 Years	rr_ExpenseExampleNoRedemptionYear05	985
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,137
1 Year	rr_AverageAnnualReturnYear01	(6.34%)
5 Years	rr_AverageAnnualReturnYear05	6.73%
10 Years	rr_AverageAnnualReturnYear10	11.01%
Since	rr_AverageAnnualReturnSinceInception	7.45%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 31, 1997
Class A, C Shares | Alger Growth & Income Fund | Return After Taxes on Distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(11.33%)
5 Years	rr_AverageAnnualReturnYear05	5.05%
10 Years	rr_AverageAnnualReturnYear10	10.19%
Since	rr_AverageAnnualReturnSinceInception	6.53%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1996
Class A, C Shares | Alger Growth & Income Fund | Return After Taxes on Distributions and Sale of Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.63%)
5 Years	rr_AverageAnnualReturnYear05	4.59%
10 Years	rr_AverageAnnualReturnYear10	8.92%
Since	rr_AverageAnnualReturnSinceInception	5.93%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1996
Class A, C Shares | Alger Growth & Income Fund | S&P 500 Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.38%)
5 Years	rr_AverageAnnualReturnYear05	8.49%
10 Years	rr_AverageAnnualReturnYear10	13.12%
Since	rr_AverageAnnualReturnSinceInception	7.70%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1996

[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.

[2] The expense information in the table has been restated to reflect a reduction in advisory fees that was effective on January 1, 2018.

[3] 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.