S000009909 [Member] Investment Strategy - AMG River Road Large Cap Value Select Fund	Oct. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	Principal Investment Strategies
Strategy Narrative [Text Block]	Under normal circumstances, the Fund invests at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in securities of large-capitalization companies. The Fund currently considers large-capitalization companies to be those with market capitalizations at the time of acquisition within the capitalization range of the Russell 1000® Index (between $2 billion and $3.192 billion as of April 30, 2025, the date of the latest reconstitution of the Index (implemented by the Index June 27, 2025)). This capitalization range will change over time. The Fund may continue to hold securities of a portfolio company that subsequently drops below or appreciates above this capitalization threshold. Because of this, the Fund may have less than 80% of its net assets in securities of large-capitalization companies at any given time. Under normal conditions, the Fund intends to invest its assets in the equity securities of a limited number of issuers. The Fund is non-diversified. The Fund invests primarily in equity securities that River Road Asset Management, LLC, the subadviser to the Fund (“River Road” or the “Subadviser”), believes are undervalued, including common stock, foreign securities (directly and through depositary receipts) and real estate investment trusts (“REITs”). Value investing involves buying stocks that River Road believes are out of favor and/or undervalued in comparison to their peers or their prospects for growth. The Fund may also invest in common stock of companies with market capitalizations that are below that of the Russell 1000® Index at the time of acquisition, convertible securities, preferred securities, and publicly traded partnerships (“PTPs”), including, but not limited to, master limited partnerships (“MLPs”). The Subadviser’s investment philosophy is based upon its proprietary Absolute Value® approach, which seeks to generate attractive, sustainable returns over the long term, with an emphasis on minimizing downside portfolio risk. The Subadviser builds the Fund’s portfolio from the bottom up, making security-specific research central to the Subadviser’s process. At the core of the Subadviser’s Absolute Value® approach is a systematic method for assessing the ‘risk-to-reward’ characteristics of an investment. The goal of the research process is to formulate two outputs from which an investment decision is made – conviction rating (risk) and discount to value (reward). A stock’s conviction rating combined with its discount to value determine not only whether the stock qualifies for investment, but also how the stock will be sized within the Fund. To seek to manage risk, the Subadviser employs a structured sell discipline.

Under normal circumstances, the Fund invests at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in securities of large-capitalization companies. The Fund currently considers large-capitalization companies to be those with market capitalizations at the time of acquisition within the capitalization range of the Russell 1000® Index (between $2 billion and $3.192 billion as of April 30, 2025, the date of the latest reconstitution of the Index (implemented by the Index June 27, 2025)). This capitalization range will change over time. The Fund may continue to hold securities of a portfolio company that subsequently drops below or appreciates above this capitalization threshold. Because of this, the Fund may have less than 80% of its net assets in securities of large-capitalization companies at any given time. Under normal conditions, the Fund intends to invest its assets in the equity securities of a limited number of issuers. The Fund is non-diversified.

The Fund invests primarily in equity securities that River Road Asset Management, LLC, the subadviser to the Fund (“River Road” or the “Subadviser”), believes are undervalued, including common stock, foreign securities (directly and through depositary receipts) and real estate investment trusts (“REITs”). Value investing involves buying stocks that River Road believes are out of favor and/or undervalued in comparison to their peers or their prospects for growth. The Fund may also invest in common stock of companies with market capitalizations that are below that of the Russell 1000® Index at the time of acquisition, convertible securities, preferred securities, and publicly traded partnerships (“PTPs”), including, but not limited to, master limited partnerships (“MLPs”).

The Subadviser’s investment philosophy is based upon its proprietary Absolute Value® approach, which seeks to generate attractive, sustainable returns over the long term, with an emphasis on minimizing downside portfolio risk.

The Subadviser builds the Fund’s portfolio from the bottom up, making security-specific research central to the Subadviser’s process. At the core of the Subadviser’s Absolute Value® approach is a systematic method for assessing the ‘risk-to-reward’ characteristics of an investment. The goal of the research process is to formulate two outputs from which an investment decision is made – conviction rating (risk) and discount to value (reward). A stock’s conviction rating combined with its discount to value determine not only whether the stock qualifies for investment, but also how the stock will be sized within the Fund.