S000025838 [Member] Investment Risks - AMG GW&K Municipal Bond Fund	Dec. 31, 2025
Debt Securities Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Debt Securities Risk—the value of a debt security changes in response to various factors, including, for example, market-related factors, such as changes in interest rates or changes in the actual or perceived ability of an issuer to meet its obligations. Investments in debt securities are subject to, among other risks, credit risk, interest rate risk, extension risk, prepayment risk and liquidity risk.
Interest Rate Risks [Member]
Prospectus [Line Items]
Risk [Text Block]	Interest Rate Risk—fixed coupon payments (cash flows) of bonds and debt securities may become less competitive with the market in periods of rising interest rates and cause bond prices to decline. During periods of increasing interest rates, the Fund may experience high levels of volatility and shareholder redemptions, and may have to sell securities at times when it would otherwise not do so, and at unfavorable prices, which could reduce the returns of the Fund.
Liquidity Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Liquidity Risk—the Fund may not be able to dispose of particular investments, such as illiquid securities, readily at favorable times or prices or the Fund may have to sell them at a loss.
Management Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Management Risk—because the Fund is an actively managed investment portfolio, security selection or focus on securities in a particular style, market sector or group of companies may cause the Fund to incur losses or underperform relative to its benchmarks or other funds with a similar investment objective. There can be no guarantee that the Subadviser’s investment techniques and risk analysis will produce the desired result.
Sector Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Sector Risk—issuers and companies that are in similar industry sectors may be similarly affected by particular economic or market events; to the extent the Fund has substantial holdings within a particular sector, the risks associated with that sector increase. A portion of the Fund's assets may be invested in fixed income securities that would tend to respond similarly to particular economic or political developments or the interest on which is based on revenues or otherwise related to similar types of projects. An example would be securities of issuers whose revenues are paid from similar types of projects, such as utilities or transportation.
Reinvestment Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Reinvestment Risk—the Fund may have difficulty reinvesting payments from debtors and may receive lower rates than from its original investments.
Prepayment Risks [Member]
Prospectus [Line Items]
Risk [Text Block]	Prepayment Risk—a debtor may exercise its right to pay back a bond or other debt security earlier than expected or required during periods of decreasing interest rates.
Municipal Market Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Municipal Market Risk—factors unique to the municipal bond market may negatively affect the value of municipal bonds. These factors include political or legislative changes, and uncertainties related to the tax status of the securities and the rights of investors in the securities. The Fund may invest in a group of municipal obligations that are related in such a way that an economic, business, or political development affecting one would also affect the others.
Inflation Deflation Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Inflation/Deflation Risk—inflation risk is the risk that the value of assets or income from investments will be worth less in the future. Inflation rates may change frequently and drastically as a result of various factors and the Fund’s investments may not keep pace with inflation, which may result in losses to Fund investors or adversely affect the real value of shareholders’ investments in the Fund. As inflation rates increase, fixed income securities markets may experience heightened levels of interest rate volatility and liquidity risk. Deflation risk is the risk that the prices throughout the economy decline over time – the opposite of inflation. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio.
Extension Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Extension Risk—during periods of rising interest rates, a debtor may pay back a bond or other fixed income security slower than expected or required, and the value of such security may fall.
Changing Distribution Level Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Changing Distribution Level Risk—the Fund will normally receive income which may include interest, dividends and/or capital gains, depending upon its investments. The distribution amount paid by the Fund will vary and generally depends on the amount of income the Fund earns (less expenses) on its portfolio holdings, and capital gains or losses it recognizes. A decline in the Fund’s income or net capital gains arising from its investments may reduce its distribution level.
Credit Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Credit Risk—the issuer of bonds or other debt securities may be unable or unwilling, or may be perceived as unable or unwilling, to make timely interest or principal payments or otherwise honor its obligations. Changes in an issuer’s financial strength, credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer.
Market Risks [Member]
Prospectus [Line Items]
Risk [Text Block]	Market Risk—market prices of investments held by the Fund may fall rapidly or unpredictably due to a variety of factors, including economic or market conditions, or other factors including terrorism, war, natural disasters and the spread of infectious illness or other public health issues, including epidemics or pandemics, or in response to events that affect particular industries or companies. In addition, unexpected political, regulatory, trade and diplomatic events within the United States and abroad may affect investor and consumer confidence and may adversely impact financial markets and the broader economy, perhaps suddenly and to a significant degree.
Risk Lose Money [Member]
Prospectus [Line Items]
Risk [Text Block]	There is the risk that you may lose money on your investment.
Risk Not Insured Depository Institution [Member]
Prospectus [Line Items]
Risk [Text Block]	An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.

S000025838 [Member] Investment Risks - AMG GW&K Municipal Bond Fund

Dec. 31, 2025

Debt Securities Risk—the value of a debt security changes in response to various factors, including, for example, market-related factors, such as changes in interest rates or changes in the actual or perceived ability of an issuer to meet its obligations. Investments in debt securities are subject to, among other risks, credit risk, interest rate risk, extension risk, prepayment risk and liquidity risk.

Prospectus [Line Items]

Risk [Text Block]

Interest Rate Risk—fixed coupon payments (cash flows) of bonds and debt securities may become less competitive with the market in periods of rising interest rates and cause bond prices to decline. During periods of increasing interest rates, the Fund

may experience high levels of volatility and shareholder redemptions, and may have to sell securities at times when it would otherwise not do so, and at unfavorable prices, which could reduce the returns of the Fund.

Liquidity Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Liquidity Risk—the Fund may not be able to dispose of particular investments, such as illiquid securities, readily at favorable times or prices or the Fund may have to sell them at a loss.

Management Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Management Risk—because the Fund is an actively managed investment portfolio, security selection or focus on securities in a particular style, market sector or group of companies may cause the Fund to incur losses or underperform relative to its benchmarks or other funds with a similar investment objective. There can be no guarantee that the Subadviser’s investment techniques and risk analysis will produce the desired result.

Sector Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Sector Risk—issuers and companies that are in similar industry sectors may be similarly affected by particular economic or market events; to the extent the Fund has substantial holdings within a particular sector, the risks associated with that sector increase. A portion of the Fund's assets may be invested in fixed income securities that would tend to respond similarly to particular economic or political developments or the interest on which is based on revenues or otherwise related to similar types of projects. An example would be securities of issuers whose revenues are paid from similar types of projects, such as utilities or transportation.

Reinvestment Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Reinvestment Risk—the Fund may have difficulty reinvesting payments from debtors and may receive lower rates than from its original investments.

Prepayment Risks [Member]

Prospectus [Line Items]

Risk [Text Block]

Prepayment Risk—a debtor may exercise its right to pay back a bond or other debt security earlier than expected or required during periods of decreasing interest rates.

Municipal Market Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Municipal Market Risk—factors unique to the municipal bond market may negatively affect the value of municipal bonds. These factors include political or legislative changes, and uncertainties related to the tax status of the securities and the rights of investors in the securities. The Fund may invest in a group of municipal obligations that are related in such a way that an economic, business, or political development affecting one would also affect the others.

Inflation Deflation Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Inflation/Deflation Risk—inflation risk is the risk that the value of assets or income from investments will be worth less in the future. Inflation rates may change frequently and drastically as a result of various factors and the Fund’s investments may not keep pace with inflation, which may result in losses to Fund investors or adversely affect the real value of shareholders’ investments in the Fund. As inflation rates increase, fixed income securities markets may experience heightened levels of interest rate volatility and liquidity risk. Deflation risk is the risk that the prices throughout the economy decline over time – the opposite of inflation. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio.

Extension Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Extension Risk—during periods of rising interest rates, a debtor may pay back a bond or other fixed income security slower than expected or required, and the value of such security may fall.

Changing Distribution Level Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Changing Distribution Level Risk—the Fund will normally receive income which may include interest, dividends and/or capital gains, depending upon its investments. The distribution amount paid by the Fund will vary and generally depends on the amount of income the Fund earns (less expenses) on its portfolio holdings, and capital gains or losses it recognizes. A decline in the Fund’s income or net capital gains arising from its investments may reduce its distribution level.

Credit Risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Credit Risk—the issuer of bonds or other debt securities may be unable or unwilling, or may be perceived as unable or unwilling, to make timely interest or principal payments or otherwise honor its obligations. Changes in an issuer’s financial strength, credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer.

Market Risks [Member]

Prospectus [Line Items]

Risk [Text Block]

Market Risk—market prices of investments held by the Fund may fall rapidly or unpredictably due to a variety of factors, including economic or market conditions, or other factors including terrorism, war, natural disasters and the spread of infectious illness or other public health issues, including epidemics or pandemics, or in response to events that affect particular industries or companies. In addition, unexpected

political, regulatory, trade and diplomatic events within the United States and abroad may affect investor and consumer confidence and may adversely impact financial markets and the broader economy, perhaps suddenly and to a significant degree.

Risk Lose Money [Member]

Prospectus [Line Items]

Risk [Text Block]

There is the risk that you may lose money on your investment.

Risk Not Insured Depository Institution [Member]

Prospectus [Line Items]

Risk [Text Block]

An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.