S000008605 [Member] Shareholder Fees - William Blair Institutional International Growth Fund - Institutional Class |
Dec. 31, 2025 |
|---|---|
| Prospectus [Line Items] | |
| Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) | 0.00% |
| Redemption Fee (as a percentage of Amount Redeemed) | 0.00% |