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S000008597 [Member] Annual Fund Operating Expenses - William Blair Small Cap Value Fund
Dec. 31, 2025
Prospectus [Line Items]  
Fee Waiver or Reimbursement over Assets, Date of Termination April 30, 2027
Class N  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.75%
Distribution and Service (12b-1) Fees 0.25%
Other Expenses (as a percentage of Assets): 0.16%
Expenses (as a percentage of Assets) 1.16%
Fee Waiver or Reimbursement 0.01% [1]
Net Expenses (as a percentage of Assets) 1.15%
Class I  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.75%
Distribution and Service (12b-1) Fees 0.00%
Other Expenses (as a percentage of Assets): 0.18%
Expenses (as a percentage of Assets) 0.93%
Fee Waiver or Reimbursement 0.04% [1]
Net Expenses (as a percentage of Assets) 0.89%
Class R6  
Prospectus [Line Items]  
Management Fees (as a percentage of Assets) 0.75%
Distribution and Service (12b-1) Fees 0.00%
Other Expenses (as a percentage of Assets): 0.05%
Expenses (as a percentage of Assets) 0.80%
Fee Waiver or Reimbursement [1]
Net Expenses (as a percentage of Assets) 0.80%
[1]
William Blair Investment Management, LLC (the “Adviser”) has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) to 1.15% and 0.89% of average daily net assets for Class N and Class I shares, respectively, until April 30, 2027. The Adviser may not terminate this arrangement prior to April 30, 2027 without the approval of the Fund’s Board of Trustees.