v3.26.1
S000079761 [Member] Average Annual Total Returns
 12 Months Ended 34 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Bloomberg US Municipal Bond Index (reflects no deduction for fees, expenses, or taxes)    
Prospectus [Line Items]    
Average Annual Return, Percent 4.25% 3.90% [1]
Performance Inception Date   Feb. 28, 2023
Bloomberg US Municipal Bond BAA Index (reflects no deduction for fees, expenses, or taxes)    
Prospectus [Line Items]    
Average Annual Return, Percent 4.13% 5.14% [1]
Performance Inception Date   Feb. 28, 2023
AMG GW&K Municipal Enhanced SMA Shares    
Prospectus [Line Items]    
Average Annual Return, Percent 2.84% 5.18% [1]
Performance Inception Date   Feb. 28, 2023
AMG GW&K Municipal Enhanced SMA Shares | After Taxes on Distributions    
Prospectus [Line Items]    
Average Annual Return, Percent 0.87% 4.33% [1]
Performance Inception Date   Feb. 28, 2023
AMG GW&K Municipal Enhanced SMA Shares | After Taxes on Distributions and Sales    
Prospectus [Line Items]    
Average Annual Return, Percent 1.64% 4.24% [1]
Performance Inception Date   Feb. 28, 2023
[1] Fund and Index performance shown reflects performance since the inception date of the Fund on February 28, 2023.