Alger Mid Cap Focus Fund Investment Strategy - Class Y Shares [Member] - Alger Mid Cap Focus 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.Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of mid-cap companies. For these purposes, “mid-cap companies” are those companies that, at the time of purchase of the securities, have total market capitalization within the range of (i) companies included in the Russell MidCap Growth Index or (ii) $1 billion to $30 billion. At December 31, 2025, the companies in this index ranged from $1.03 billion 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. Equity securities include common or preferred stocks that are listed on U.S. or foreign exchanges.In addition, under normal market conditions, the Fund invests at least 25% of its total assets in companies in the following group of industries: Health Care Equipment & Supplies, Health Care Technology, Biotechnology, Life Sciences Tools & Services, and/or Software, as defined by third party sources. The Fund may have 25% or more of its total assets invested in any one of these industries.As a focus fund, the Fund intends to invest a substantial portion of its assets in a smaller number of issuers. Generally the Fund will own approximately 50 holdings. Fund holdings may occasionally differ from this number for a variety of reasons, including, among others, because of extreme market volatility, such as when the Fund has entered a temporary defensive position.  Additionally, the Fund may temporarily exceed the stated number of holdings for a number of reasons, including, but not limited to, when it acquires a new holding and determines that it is in the best interests of shareholders to sell an existing holding over a period of time, instead of immediately selling the entire holding.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 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, industrials, communication services, and health care sectors. For the purpose of categorizing companies, sectors are a broader category than industries and industries comprise sectors.The Fund can also invest in privately placed securities, which are securities acquired in non-public offerings for which there is no readily available market.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.