v3.25.4
S000001125 [Member] Annual Fund Operating Expenses - AMG River Road Mid Cap Value Fund
Oct. 31, 2025
Prospectus [Line Items]  
Fee Waiver or Reimbursement over Assets, Date of Termination March 1, 2027
CLASS N SHARES  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.56%
Distribution and Service (12b-1) Fees 0.25%
Other Expenses (as a percentage of Assets): 0.33% [1]
Expenses (as a percentage of Assets) 1.14%
Fee Waiver or Reimbursement (0.03%) [2]
Net Expenses (as a percentage of Assets) 1.11% [2]
CLASS I SHARES  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.56%
Distribution and Service (12b-1) Fees 0.00%
Other Expenses (as a percentage of Assets): 0.28% [1]
Expenses (as a percentage of Assets) 0.84%
Fee Waiver or Reimbursement (0.03%) [2]
Net Expenses (as a percentage of Assets) 0.81% [2]
Class Z Shares  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.56%
Distribution and Service (12b-1) Fees 0.00%
Other Expenses (as a percentage of Assets): 0.23% [1]
Expenses (as a percentage of Assets) 0.79%
Fee Waiver or Reimbursement (0.03%) [2]
Net Expenses (as a percentage of Assets) 0.76% [2]
[1] Expense information has been restated to reflect current fees.
[2] AMG Funds LLC (the “Investment Manager”) has contractually agreed, through at least March 1, 2027, to waive management fees and/or pay or reimburse the Fund’s expenses in order to limit Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of taxes, interest (including interest incurred in connection with bank and custody overdrafts and in connection with securities sold short), shareholder servicing fees, distribution and service (12b-1) fees, brokerage commissions and other transaction costs, dividends payable with respect to securities sold short, acquired fund fees and expenses, and extraordinary expenses) of the Fund to the annual rate of 0.76% of the Fund’s average daily net assets (this annual rate or such other annual rate that may be in effect from time to time, the “Expense Cap”), subject to later reimbursement by the Fund in certain circumstances. In general, for a period of up to 36 months after the date any amounts are paid, waived or reimbursed by the Investment Manager, the Investment Manager may recover such amounts from the Fund, provided that such repayment would not cause the Fund’s Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of the items noted in the parenthetical above) to exceed either (i) the Expense Cap in effect at the time such amounts were paid, waived or reimbursed, or (ii) the Expense Cap in effect at the time of such repayment by the Fund. The contractual expense limitation may only be terminated in the event the Investment Manager or a successor ceases to be the investment manager of the Fund or a successor fund, by mutual agreement between the Investment Manager and the AMG Funds IV Board of Trustees or in the event of the Fund’s liquidation unless the Fund is reorganized or is a party to a merger in which the surviving entity is successor to the accounting and performance information of the Fund.