Alger Mid Cap Focus Fund Performance Management - Class Z Shares [Member] - Alger Mid Cap Focus Fund	Oct. 31, 2025
Prospectus [Line Items]
Bar Chart and Performance Table [Heading]	<span style="color:#0064FA;font-family:Arial;font-size:10pt;font-weight:bold;">Performance</span>
Performance Narrative [Text Block]	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. The bar chart shows how the Fund’s average annual returns have varied over the indicated periods. The table shows how the Fund’s average annual returns compare with those of an appropriate broad-based securities market index that represents the overall domestic equity market and a more narrowly based index that reflects the market sectors in which the Fund invests. 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 Past Does Not Indicate Future [Text]	<span style="color:#262626;font-family:Arial;font-size:9pt;">The Fund’s past performance (before and after taxes) is not necessarily an indication of </span><span style="color:#262626;font-family:Arial;font-size:9pt;">how it will perform in the future.</span>
Performance Information Illustrates Variability of Returns [Text]	<span style="color:#262626;font-family:Arial;font-size:9pt;">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. The bar chart shows how the Fund’s average annual returns have varied over the indicated periods. The table shows how the Fund’s average annual returns compare with those of an appropriate broad-based securities market index that represents the overall domestic equity market and a more narrowly based index that reflects the market sectors in which the Fund invests. </span>
Bar Chart [Heading]	<span style="color:#262626;font-family:Arial;font-size:10pt;font-weight:bold;">Annual Total Return for Class Z Shares</span><span style="color:#262626;font-family:Arial;font-size:10pt;line-height:12pt;"> </span><span style="color:#262626;font-family:Arial;font-size:10pt;font-style:italic;">as of December 31 (%)</span>
Bar Chart Closing [Text Block]	Best Quarter:Q2 202036.83%Worst Quarter:Q2 2022-28.04%
Performance Table Heading	<span style="color:#0064FA;font-family:Arial;font-size:10pt;font-weight:bold;">Average Annual Total Return as of December 31, 2025</span>
Performance Table Narrative	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.
Performance Table Uses Highest Federal Rate	<span style="color:#262626;font-family:Arial;font-size:9pt;">after-tax returns are calculated using the historical highest individual federal marginal income tax rates and </span><span style="color:#262626;font-family:Arial;font-size:9pt;">do not reflect the impact of state and local taxes.</span>
Performance Table Not Relevant to Tax Deferred	<span style="color:#262626;font-family:Arial;font-size:9pt;">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.</span>
Performance Availability Website Address [Text]	<span style="color:#262626;font-family:Arial;font-size:9pt;">www.alger.com</span>
Class Z
Prospectus [Line Items]
Highest Quarterly Return, Label [Optional Text]	<span style="color:#262626;font-family:Arial;font-size:8pt;font-weight:bold;">Best Quarter:</span>
Highest Quarterly Return	36.83%
Highest Quarterly Return, Date	Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text]	<span style="color:#262626;font-family:Arial;font-size:8pt;font-weight:bold;">Worst Quarter:</span>
Lowest Quarterly Return	(28.04%)
Lowest Quarterly Return, Date	Jun. 30, 2022