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Label

Element

Value

Risk/Return:

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Risk/Return [Heading]

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Alger Mid Cap Growth Fund

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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Alger Mid Cap Growth Fund seeks long-term capital appreciation.

Expense [Heading]

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Fund Fees and Expenses

Expense Narrative [Text Block]

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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" beginning on page A-2 of the Fund's Prospectus and 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]

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Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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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 194.81% of the average value of its portfolio.

Portfolio Turnover, Rate

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Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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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.

Expense Example by, Year, Caption [Text]

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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]

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You would pay the following expenses if you did not redeem your shares:

Strategy [Heading]

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Principal Investment Strategy

Strategy Narrative [Text Block]

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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, significantly growing demand or market dominance. Positive Lifecycle Change companies are, for example, companies benefitting from regulatory change, a new product introduction or management change.

The Fund focuses on mid-sized companies that Fred Alger Management, Inc. believes demonstrate promising growth potential. Under normal circumstances, the Fund invests at least 80% of its net assets in equity securities of companies that, at the time of purchase of the securities, have total market capitalization within the range of companies included in the Russell Midcap Growth Index or the S&P MidCap 400 Index, as reported by the indexes as of the most recent quarter-end. Both indexes are designed to track the performance of medium-capitalization stocks. At December 31, 2014, the market capitalization of the companies in these indexes ranged from $275.2 million to $33.5 billion.

The Fund can also invest in derivative instruments. The Fund currently expects that its primary uses of derivatives will involve: (1) purchasing put and call options and selling (writing) covered put and call options, on securities and securities indexes, to increase gain, to hedge against the risk of unfavorable price movements in the underlying securities, or to provide diversification of risk, and (2) entering into forward currency contracts to hedge the Fund's foreign currency exposure when it holds, or proposes to hold, non-U.S. dollar denominated securities.

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Principal Risks

Risk Narrative [Text Block]

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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.

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.

A small investment in derivatives could have a potentially large impact on the Fund's performance. When purchasing options, the Fund bears the risk that if the market value of the underlying security does not move to a level that would make exercise of the option profitable, the option will expire unexercised. When a call option written by the Fund is exercised, the Fund will not participate in any increase in the underlying security's value above the exercise price. When a put option written by the Fund is exercised, the Fund will be required to purchase the underlying security at a price in excess of its market value. Use of options on securities indexes is subject to the risk that trading in the options may be interrupted if trading in certain securities included in the index is interrupted, the risk that price movements in the Fund's portfolio securities may not correlate precisely with movements in the level of an index, and the risk that Fred Alger Management, Inc. may not predict correctly movements in the direction of a particular market or of the stock market generally. Because certain options may require settlement in cash, the Fund may be forced to liquidate portfolio securities to meet settlement obligations. Forward currency contracts are subject to currency exchange rate risks and the risk of non-performance by the contract counterparty.

The following risks may also apply:

• there may be greater risk in investing in medium-capitalization companies rather than larger, more established companies due to such factors as inexperienced management and limited product lines or financial resources.

• it may 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.

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.

Risk Lose Money [Text]

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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.

Risk Not Insured Depository Institution [Text]

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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]

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Performance

Performance Narrative [Text Block]

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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. Remember that 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]

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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]

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www.alger.com

Performance Past Does Not Indicate Future [Text]

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Remember that 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]

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Annual Total Return for Class A Shares as of December 31 (%)

Bar Chart Does Not Reflect Sales Loads [Text]

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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]

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Best Quarter:
Q2 2009 19.64%

Worst Quarter:
Q4 2008 -32.40%

Highest Quarterly Return, Label

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Best Quarter:

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

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Lowest Quarterly Return, Label

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Worst Quarter:

Lowest Quarterly Return, Date

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Dec. 31, 2008

Lowest Quarterly Return

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Index No Deduction for Fees, Expenses, Taxes [Text]

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(reflects no deduction for fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

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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.

Performance Table Not Relevant to Tax Deferred

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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]

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After-tax returns for Class B and C Shares, which are not shown, will vary from those shown for Class A Shares.

Performance Table Explanation after Tax Higher

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A "Return After Taxes on Distributions and Sale of Fund Shares" may sometimes be higher than the other two return figures; this happens where there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.

Performance Table Closing [Text Block]

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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 B and 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 where there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.

rr_AverageAnnualReturnCaption

Average Annual Total Return as of December 31, 2014

Russell Midcap Growth Index (reflects no deduction for fees, expenses or taxes)

Risk/Return:

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Average Annual Returns, 1 Year

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Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 1996

Alger MidCap Growth Fund Class A

Risk/Return:

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Maximum sales charge (load) imposed on purchases as a % of offering price

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Maximum deferred sales charge (load) as a % of purchase price or redemption proceeds, whichever is lower

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^[2]

Management Fees

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Distribution and/or Service (12b-1) Fees

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Total Annual Fund Operating Expenses

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Expenses Deferred Charges [Text Block]

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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]

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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]

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Expense Example, with Redemption, 1 Year

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Expense Example, with Redemption, 3 Years

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Expense Example, with Redemption, 5 Years

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Expense Example, with Redemption, 10 Years

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Expense Example, No Redemption, 1 Year

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Expense Example, No Redemption, 3 Years

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Expense Example, No Redemption, 5 Years

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Expense Example, No Redemption, 10 Years

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Annual Return 2005

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Annual Return 2006

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Annual Return 2007

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Annual Return 2008

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Annual Return 2009

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Annual Return 2010

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Annual Return 2011

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Annual Return 2012

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Annual Return 2013

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Annual Return 2014

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Average Annual Returns, 1 Year

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Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 1996

Alger MidCap Growth Fund Class A | After Taxes on Distributions

Risk/Return:

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Average Annual Returns, 1 Year

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Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Alger MidCap Growth Fund Class A | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

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Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Alger MidCap Growth Fund Class B

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

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Management Fees

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Distribution and/or Service (12b-1) Fees

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Total Annual Fund Operating Expenses

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Expense Example, with Redemption, 1 Year

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Expense Example, with Redemption, 3 Years

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Expense Example, with Redemption, 5 Years

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Expense Example, with Redemption, 10 Years

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Expense Example, No Redemption, 1 Year

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Expense Example, No Redemption, 3 Years

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Expense Example, No Redemption, 5 Years

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Expense Example, No Redemption, 10 Years

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Average Annual Returns, 1 Year

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Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Average Annual Returns, Inception Date

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May 24, 1993

Alger MidCap Growth 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

Management Fees

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Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

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Total Annual Fund Operating Expenses

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Expense Example, with Redemption, 1 Year

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Expense Example, with Redemption, 3 Years

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Expense Example, with Redemption, 5 Years

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Expense Example, with Redemption, 10 Years

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Expense Example, No Redemption, 1 Year

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Expense Example, No Redemption, 3 Years

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Expense Example, No Redemption, 5 Years

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Expense Example, No Redemption, 10 Years

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Average Annual Returns, 1 Year

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Average Annual Returns, 5 Years

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Average Annual Returns, 10 Years

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Average Annual Returns, Since Inception

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^[1]

Average Annual Returns, Inception Date

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Jul. 31, 1997

[1]	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. Since inception performance of the Fund's Class B Shares is available upon request.
[2]	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.