Alger Weatherbie Specialized Growth Fund Investment Strategy - Class Z Shares [Member] - Alger Weatherbie Specialized Growth Fund	Oct. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#0064FA;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Investment Strategy</span>
Strategy Narrative [Text Block]	The Manager believes companies undergoing Positive Dynamic Change offer the best 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 is sub-advised by Weatherbie Capital, LLC (“Weatherbie”), an affiliate of the Manager (Weatherbie and the Manager, collectively referred to as the “Manager,” where applicable). Subject to the general supervision by the Fund’s Board of Trustees, the Manager oversees Weatherbie and evaluates its performance results. The Manager reviews portfolio performance, compliance with investment guidelines and federal securities laws, and changes in key personnel of Weatherbie. Weatherbie is primarily responsible for the day-to-day management of the Fund’s portfolio, including purchases and sales of individual securities.Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of smallcap and midcap companies. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges. Smallcap or midcap companies are companies that, at the time of purchase, have total market capitalization within the range of companies included in the Russell 2500 Growth Index or the Russell Midcap Growth Index, respectively. At December 31, 2025, the market capitalization of the companies in these indexes ranged from $12.47 million to $101.64 billion. Because of the Fund’s long-term approach to investing, it could have a significant portion of its assets invested in securities of issuers that have appreciated beyond the market capitalization thresholds noted. As a focus fund, the Fund intends to invest a substantial portion of its assets in a smaller number of issuers, and may focus its holdings in fewer business sectors or industries. Generally the Fund will own approximately 50 holdings. Fund holdings may occasionally exceed this number for a variety of reasons.The Fund may invest a significant portion of its assets in securities of companies conducting business within a single sector, as defined by third party sources, including, but not limited to, the information technology, health care, industrials, and financials sectors. For the purpose of categorizing companies, sectors are a broader category than industries and industries comprise sectors.The Fund may sell a stock when it reaches a target price, it fails to perform as expected, or other opportunities appear more attractive. As a result, the Fund may engage in active trading of portfolio securities.The Fund can invest in foreign securities.The Fund may invest in cash (and cash equivalents) when the Fund is unable to find enough attractive long-term investments to meet its investment objective, to meet redemptions and/or when the Manager believes it is advisable to do so during times of short-term market volatility. During these times, cash (and cash equivalents) will not exceed 15% of the Fund’s net assets.

Alger Weatherbie Specialized Growth Fund Investment Strategy - Class Z Shares [Member] - Alger Weatherbie Specialized Growth Fund

Oct. 31, 2025

<span style="color:#0064FA;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Investment Strategy</span>

Strategy Narrative [Text Block]

The Manager believes companies undergoing Positive Dynamic Change offer the best 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 is sub-advised by Weatherbie Capital, LLC (“Weatherbie”), an affiliate of the Manager (Weatherbie and the Manager, collectively referred to as the “Manager,” where applicable). Subject to the general supervision by the Fund’s Board of Trustees, the Manager oversees Weatherbie and evaluates its performance results. The Manager reviews portfolio performance, compliance with investment guidelines and federal securities laws, and changes in key personnel of Weatherbie. Weatherbie is primarily responsible for the day-to-day management of the Fund’s portfolio, including purchases and sales of individual securities.Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of smallcap and midcap companies. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges. Smallcap or midcap companies are companies that, at the time of purchase, have total market capitalization within the range of companies included in the Russell 2500 Growth Index or the Russell Midcap Growth Index, respectively. At December 31, 2025, the market capitalization of the companies in these indexes ranged from $12.47 million to $101.64 billion. Because of the Fund’s long-term approach to investing, it could have a significant portion of its assets invested in securities of issuers that have appreciated beyond the market capitalization thresholds noted. As a focus fund, the Fund intends to invest a substantial portion of its assets in a smaller number of issuers, and may focus its holdings in fewer business sectors or industries. Generally the Fund will own approximately 50 holdings. Fund holdings may occasionally exceed this number for a variety of reasons.The Fund may invest a significant portion of its assets in securities of companies conducting business within a single sector, as defined by third party sources, including, but not limited to, the information technology, health care, industrials, and financials sectors. For the purpose of categorizing companies, sectors are a broader category than industries and industries comprise sectors.The Fund may sell a stock when it reaches a target price, it fails to perform as expected, or other opportunities appear more attractive. As a result, the Fund may engage in active trading of portfolio securities.The Fund can invest in foreign securities.The Fund may invest in cash (and cash equivalents) when the Fund is unable to find enough attractive long-term investments to meet its investment objective, to meet redemptions and/or when the Manager believes it is advisable to do so during times of short-term market volatility. During these times, cash (and cash equivalents) will not exceed 15% of the Fund’s net assets.