Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	ALGER FUNDS
Prospectus Date	rr_ProspectusDate	Mar. 01, 2019
Class Z Shares | Alger Capital Appreciation Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<b>ALGER CAPITAL APPRECIATION FUND</b>
Objective [Heading]	rr_ObjectiveHeading	<b>Investment Objective</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Alger Capital Appreciation Fund seeks long-term capital appreciation.
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.
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 example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 67.33% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	67.33%
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>Example</b>
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. 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	<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. Under normal market circumstances, the Fund invests at least 85% of its net assets, plus any borrowings for investment purposes, in equity securities of companies of any market capitalization that Fred Alger Management, Inc. believes demonstrate promising growth potential. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges. 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. The Fund can leverage, that is, borrow money to purchase additional securities. By borrowing money, the Fund has the potential to increase its returns if the increase in the value of the securities purchased exceeds the cost of borrowing, including interest paid on the money borrowed. However, leverage also has the potential to magnify any decrease in the value of the purchased securities. 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, and health care sectors.
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. 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. 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. Leverage Risk – The cost of borrowing money to leverage may exceed the returns for the securities purchased or the securities purchased may actually go down in value; thus, the Fund’s net asset value may decrease more quickly than if the Fund had not borrowed.
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. 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 Z Shares</b> as of December 31 (%)
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter: Q1 2012 16.75%               Worst Quarter: Q4 2018 -15.95%
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 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. 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 Z Shares | Alger Capital Appreciation Fund | Class Z
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Advisory Fees	rr_ManagementFeesOverAssets	0.76%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.87%
1 Year	rr_ExpenseExampleYear01	$ 89
3 Years	rr_ExpenseExampleYear03	278
5 Years	rr_ExpenseExampleYear05	482
10 Years	rr_ExpenseExampleYear10	1,073
1 Year	rr_ExpenseExampleNoRedemptionYear01	89
3 Years	rr_ExpenseExampleNoRedemptionYear03	278
5 Years	rr_ExpenseExampleNoRedemptionYear05	482
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,073
2011	rr_AnnualReturn2011	(0.69%)
2012	rr_AnnualReturn2012	18.27%
2013	rr_AnnualReturn2013	35.31%
2014	rr_AnnualReturn2014	13.50%
2015	rr_AnnualReturn2015	6.56%
2016	rr_AnnualReturn2016	0.66%
2017	rr_AnnualReturn2017	31.69%
2018	rr_AnnualReturn2018	(0.66%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<b>Best Quarter:</b>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.75%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<b> Worst Quarter:</b>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(15.95%)
1 Year	rr_AverageAnnualReturnYear01	(0.66%)
5 Years	rr_AverageAnnualReturnYear05	9.76%
Since Inception	rr_AverageAnnualReturnSinceInception	12.27%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 29, 2010
Class Z Shares | Alger Capital Appreciation Fund | Return After Taxes on Distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.02%)
5 Years	rr_AverageAnnualReturnYear05	7.66%
Since Inception	rr_AverageAnnualReturnSinceInception	10.56%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 29, 2010
Class Z Shares | Alger Capital Appreciation Fund | Return After Taxes on Distributions and Sale of Shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.61%
5 Years	rr_AverageAnnualReturnYear05	7.39%
Since Inception	rr_AverageAnnualReturnSinceInception	9.68%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 29, 2010
Class Z Shares | Alger Capital Appreciation Fund | Russell 1000 Growth Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.51%)
5 Years	rr_AverageAnnualReturnYear05	10.40%
Since Inception	rr_AverageAnnualReturnSinceInception	12.59%

[1] The Fund and Fred Alger Management, Inc. have adopted fee breakpoints for Alger Capital Appreciation Fund. The advisory fee for assets up to $2 billion is .81%. The advisory fee for assets between $2 billion and $3 billion is .65%, for assets between $3 billion and $4 billion is .60%, for assets between $4 billion and $5 billion is .55%, and for assets in excess of $5 billion is .45%. The actual rate paid as a percentage of average daily net assets for the period ended October 31, 2018, was .76%.