S000009868 [Member] Investment Strategy - AMG GW&K ESG Bond Fund	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	Principal Investment Strategies
Strategy Narrative [Text Block]	The Fund seeks to achieve its objective by investing in a diversified portfolio of fixed income securities. Under normal circumstances, the Fund invests at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in bonds (debt securities). The term “bond” includes any debt or fixed income securities. Up to 30% of the Fund’s assets may be invested in below investment grade securities (commonly known as “junk bonds” or “high yield securities”). Below investment grade securities are rated below Baa3 by Moody’s Investors Service, Inc. (“Moody’s”) or below BBB- by S&P Global Ratings (“S&P”) or similarly rated by another nationally recognized statistical rating organization (“NRSRO”), or unrated but determined by GW&K Investment Management, LLC, the subadviser to the Fund (“GW&K” or the “Subadviser”), to be of comparable credit quality. In cases where the credit ratings agencies have assigned different credit ratings to the same security, the Fund will use the median rating when three NRSROs provide ratings (split-to-middle). When ratings are available from only two NRSROs, the Fund will assign the lower of the two ratings (split-to-low). The Fund may continue to hold securities that are downgraded in credit rating subsequent to their purchase if GW&K believes it would be advantageous to do so. While the Fund may purchase debt securities of any duration, the Fund currently intends to primarily invest in debt securities so that the average effective duration of the Fund’s portfolio will remain +/- 20% of the average effective duration of its benchmark, the Bloomberg U.S. Aggregate Bond Index, which was 5.88 years as of February 28, 2026. The average effective duration of debt securities in the Fund’s portfolio may, however, be shorter or longer depending on market conditions. The Fund may invest in debt securities issued by any of the following: public and private U.S. and non-U.S. companies; the U.S. government and its agencies, such as the Federal Home Loan Bank; state and local governments issuing taxable municipal securities; and governments, government agencies, authorities or instrumentalities and supra-national organizations in foreign countries, including emerging markets. The Fund may also invest in asset-backed and mortgage-backed debt securities. The Fund may invest in exchange-traded funds (“ETFs”) to gain exposure to certain bond sectors such as bank loans. The Fund may also invest in Treasury Inflation Protected Securities (“TIPS”) and preferred securities. Up to 10% of the Fund’s assets may be invested in non-U.S. dollar-denominated instruments, including sovereign and corporate bonds. The Fund may also invest in bonds whose proceeds are reserved for financing the implementation of the United Nations’ Sustainable Development Goals or other sustainable projects. GW&K’s investment process involves fundamental credit research and GW&K’s analysis of how the Fund’s potential investments are affected by material environmental, social and governance (“ESG”) factors. In selecting potential investments for the Fund, GW&K uses top-down research that focuses on managing duration, yield curve, credit quality, volatility and liquidity, as well as bottom-up research that focuses on fundamental analysis, valuation analysis, technical analysis, and ESG factor analysis. GW&K may adjust its assessment of an investment based on a number of considerations. GW&K applies its ESG factor analysis as one element of the investment process when selecting debt securities issued by public and private companies, including corporate bonds and preferred securities, state and local governments issuing taxable municipal securities, and bonds whose proceeds are reserved for financing the implementation of the United Nations’ Sustainable Development Goals or other sustainable projects, but not when selecting debt securities issued by other types of issuers, including but not limited to asset-backed and mortgage-backed debt securities, ETFs, TIPS, non-U.S. dollar-dominated instruments, and securities issued by the U.S. government and its agencies, such as the Federal Home Loan Bank, and governments, government agencies, authorities or instrumentalities and supra-national organizations in foreign countries. GW&K has created its own proprietary ESG Scoring System, which takes into consideration a range of factors, including independent analysis from third parties such as MSCI Inc. and Sustainalytics, as well as its own analysis of material ESG factors. Each of GW&K’s sector specialists generally assesses the materiality of relevant environmental, social and governance metrics to bond issues during the fundamental research process, depending on the sector and for corporate issuers the nature of the company’s business. GW&K uses standards developed by the Sustainable Accounting Standards Board to inform these assessments. Environmental assessment may take into account issues such as carbon emissions, natural resource usage, hazardous waste, chemical safety, water stress and sustainable technology. Social assessment may take into account issues such as human rights, labor relations, employee safety, product safety, data security and community relations. Governance assessment may take into account issues such as business ethics, board quality, board composition, compensation practices, financial reporting and stakeholder governance. GW&K recognizes that the relative impact of ESG factors on investment performance may vary across market sector, industries and regions, but the firm believes that responsible corporate behavior with respect to ESG factors can contribute to positive and sustainable long-term financial performance. GW&K seeks to identify issuers that GW&K believes are leaders in their industries in effectively addressing exposure to ESG risks through business practices, policies and programs, or issuers within an industry that have more limited exposure to ESG risks. The goal of the ESG factor analysis is to seek investments with lesser exposure to, or better management of, ESG risks.

Under normal circumstances, the Fund invests at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in bonds (debt securities). The term “bond” includes any debt or fixed income securities. Up to 30% of the Fund’s assets may be invested in below investment grade securities (commonly known as “junk bonds” or “high yield securities”). Below investment grade securities are rated below Baa3 by Moody’s Investors Service, Inc. (“Moody’s”) or below BBB- by S&P Global Ratings (“S&P”) or similarly rated by another nationally recognized statistical rating organization (“NRSRO”), or unrated but determined by GW&K Investment Management, LLC, the subadviser to the Fund (“GW&K” or the “Subadviser”), to be of comparable credit quality. In cases where the credit ratings agencies have assigned different credit ratings to the same security, the Fund will use the median rating when three NRSROs provide ratings (split-to-middle). When ratings are available from only two NRSROs, the Fund will assign the lower of the two ratings (split-to-low). The Fund may continue to hold securities that are downgraded in credit rating subsequent to their purchase if GW&K believes it would be advantageous to do so. While the Fund may purchase debt securities of any duration, the Fund currently intends to primarily invest in debt securities so that the average effective duration of the Fund’s portfolio will remain +/- 20% of the average effective duration of its benchmark, the Bloomberg U.S. Aggregate Bond Index, which was 5.88 years as of February 28, 2026. The average effective duration of debt securities in the Fund’s portfolio may, however, be shorter or longer depending on market conditions.

authorities or instrumentalities and supra-national organizations in foreign countries, including emerging markets. The Fund may also invest in asset-backed and mortgage-backed debt securities. The Fund may invest in exchange-traded funds (“ETFs”) to gain exposure to certain bond sectors such as bank loans. The Fund may also invest in Treasury Inflation Protected Securities (“TIPS”) and preferred securities. Up to 10% of the Fund’s assets may be invested in non-U.S. dollar-denominated instruments, including sovereign and corporate bonds. The Fund may also invest in bonds whose proceeds are reserved for financing the implementation of the United Nations’ Sustainable Development Goals or other sustainable projects. GW&K’s investment process involves fundamental credit research and GW&K’s analysis of how the Fund’s potential investments are affected by material environmental, social and governance (“ESG”) factors. In selecting potential investments for the Fund, GW&K uses top-down research that focuses on managing duration, yield curve, credit quality, volatility and liquidity, as well as bottom-up research that focuses on fundamental analysis, valuation analysis, technical analysis, and ESG factor analysis. GW&K may adjust its assessment of an investment based on a number of considerations.

GW&K applies its ESG factor analysis as one element of the investment process when selecting debt securities issued by public and private companies, including corporate bonds and preferred securities, state and local governments issuing taxable municipal securities, and bonds whose proceeds are reserved for financing the implementation of the United Nations’ Sustainable Development Goals or other sustainable projects, but not when selecting debt securities issued by other types of issuers, including but not limited to asset-backed and mortgage-backed debt securities, ETFs, TIPS, non-U.S. dollar-dominated instruments, and securities issued by the U.S. government and its agencies, such as the Federal Home Loan Bank, and governments, government agencies, authorities or instrumentalities and supra-national organizations in foreign countries. GW&K has created its own proprietary ESG Scoring System, which takes into consideration a range of factors, including independent analysis from third parties such as MSCI Inc. and Sustainalytics, as well as its own analysis of material ESG factors. Each of GW&K’s sector specialists generally assesses the materiality of relevant environmental, social and governance metrics to bond issues during the fundamental research process, depending on the sector and for corporate issuers the nature of the company’s business. GW&K uses standards developed by the Sustainable Accounting Standards Board to inform these assessments. Environmental assessment may take into account issues such as carbon emissions, natural resource usage, hazardous waste, chemical safety, water stress and sustainable technology. Social assessment may take into account issues such as human rights, labor relations, employee safety, product safety, data security and community relations. Governance assessment may take into account issues such as business ethics, board quality, board composition, compensation practices, financial reporting and stakeholder governance.

GW&K recognizes that the relative impact of ESG factors on investment performance may vary across market sector, industries and regions, but the firm believes that responsible corporate behavior with respect to ESG factors can contribute to positive and sustainable long-term financial performance. GW&K seeks to identify issuers that GW&K believes are leaders in their industries in effectively addressing exposure to ESG risks through business practices, policies and programs, or issuers