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Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Alger Large Cap Growth Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

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

Expense [Heading] rr_ExpenseHeading FUND FEES AND EXPENSES
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. There are no sales charges on purchases or redemptions.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading PORTFOLIO TURNOVER
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 148.66% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 148.66%
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE
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.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption Although your actual costs may be higher or lower, based on these assumptions you would pay the following expenses regardless of whether you redeemed your shares at the end of each period:
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGY
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, 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 growing companies that generally have broad product lines, markets, financial resources and depth of management. 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 a market capitalization equal to or greater than the market capitalization of companies included in the Russell 1000 Growth Index, as reported by the index as of the most recent quarter-end. This index is designed to track the performance of large-capitalization growth stocks. At December 31, 2012, the market capitalization of the companies in this index ranged from $417.8 million to $498.4 billion.


The Board of Trustees of the Fund has approved further narrowing the Fund's investment focus within the range set forth above. Under normal circumstances, the Fund intends to invest at least 80% of its net assets in equity securities of companies that, at the time of purchase of the securities, have a market capitalization greater than $10 billion. The Fund will not purchase securities of companies that, at the time of purchase of the securities, have a market capitalization less than $4 billion. Additionally, the Fund will generally limit its investments to between 70 and 100 holdings.


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.

Risk [Heading] rr_RiskHeading PRINCIPAL RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

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.


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] rr_RiskLoseMoney 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] 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 PERFORMANCE
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. 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] 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 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] rr_BarChartHeading ANNUAL TOTAL RETURN FOR CLASS Z SHARES as of December 31 (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter:


Q3 2012      14.29%


Worst Quarter:


Q3 2011      -14.31%

Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.29%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (14.31%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate 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 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 where there is a capital loss on redemptions, giving rise to a tax benefit to the shareholder.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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 rr_AverageAnnualReturnCaption Average Annual Total Return as of December 31, 2012
Russell 1000 Growth Index (reflects no deduction for fees, expenses or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.26%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 8.59%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 29, 2010
Alger Large Cap Growth Fund Class Z
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_MaximumAccountFeeOverAssets none
Management Fees rr_ManagementFeesOverAssets 0.71% [1]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.96%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 98
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 306
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 531
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,178
Annual Return 2011 rr_AnnualReturn2011 (0.34%)
Annual Return 2012 rr_AnnualReturn2012 9.77%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 9.77%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.45%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 29, 2010
Alger Large Cap Growth Fund Class Z | Return After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 9.35%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.25%
Alger Large Cap Growth Fund Class Z | Return After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 6.35%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 3.68%
[1] The Fund and Fred Alger Management, Inc. have adopted fee breakpoints for Alger Large Cap Growth Fund. The management fee for assets in excess of $1 billion is .60%.