Label

Element

Value

Risk/Return:

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Risk/Return [Heading]

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Alger Growth Opportunities Fund

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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Alger Growth Opportunities 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.

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)

Fee Waiver or Reimbursement over Assets, Date of Termination

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2016-02-28

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 example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 91.91% of the average value of its portfolio.

Portfolio Turnover, Rate

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91.91%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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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.

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 regardless of whether or not you redeemed your shares at the end of each period:

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 invests primarily in the stock of small, fast-growing companies that Fred Alger Management, Inc. believes offer innovative products, services or technologies to a rapidly-expanding marketplace. Although the Fund may invest without limit in companies of any size, the Fund focuses on companies that, at the time of purchase of the securities, have a total market capitalization not exceeding the highest market capitalization of companies included in the Russell 2500 Growth Index, as reported by the index as of the most recent quarter-end. This index is designed to track the performance of small and medium capitalization stocks. At December 31, 2014, the highest market capitalization of the companies in this index was $17.9 billion.

The Fund intends to invest a substantial portion of its assets in a small number of issuers, and may therefore concentrate its holdings in fewer business sectors or industries.

The Fund can leverage, that is, borrow money to buy 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.

Risk [Heading]

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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.

The following risks may also apply:

•  there may be greater risk in investing in companies with small or medium market capitalizations 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.

•  the Fund may have a more concentrated portfolio than other funds, so it may be more vulnerable to changes in the market value of a single issuer and may be more susceptible to risks associated with a single economic, political or regulatory occurrence than a fund that has a more diversified portfolio.

•  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 could decrease more quickly than if it had not borrowed.

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. 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 Z Shares as of December 31 (%)

Bar Chart Closing [Text Block]

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Best Quarter:
Q1 2012 14.33% Worst Quarter:
Q3 2011 -22.98%

Highest Quarterly Return, Label

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Best Quarter:

Highest Quarterly Return, Date

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Mar. 31, 2012

Highest Quarterly Return

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14.33%

Lowest Quarterly Return, Label

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Worst Quarter:

Lowest Quarterly Return, Date

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Sep. 30, 2011

Lowest Quarterly Return

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(22.98%)

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 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. 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.

Caption

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Average Annual Total Return as of December 31, 2014

Russell 2500 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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7.05%

Average Annual Returns, Since Inception

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14.34%

Average Annual Returns, Inception Date

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Dec. 29, 2010

Alger Growth Opportunities Fund Class Z

Risk/Return:

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Shareholder Fees (fees paid directly from your investment)

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none

Management Fees

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0.85%

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

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

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1.26%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.11%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(1.12%)

^[1]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.99%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

101

Expense Example, with Redemption, 3 Years

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553

Expense Example, with Redemption, 5 Years

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1,031

Expense Example, with Redemption, 10 Years

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2,353

Annual Return 2011

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(4.79%)

Annual Return 2012

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14.22%

Annual Return 2013

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38.63%

Annual Return 2014

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2.16%

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

2.16%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

11.26%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 2010

Alger Growth Opportunities Fund Class Z | After Taxes on Distributions

Risk/Return:

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Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

0.16%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

8.65%

Alger Growth Opportunities Fund Class Z | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

2.87%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

8.73%

[1] Fred Alger Management, Inc. has contractually agreed to reimburse Fund expenses (excluding interest, taxes, brokerage, and extraordinary expenses) through February 28, 2016 to the extent necessary to limit the annual operating expenses of Class Z Shares of the Fund to .99% of the class's average net assets. This expense reimbursement cannot be terminated. Fred Alger Management, Inc. may recoup reimbursed expenses during the one-year term of the expense reimbursement contract if the expense ratio falls below the stated limitation.