S000008603 [Member] Expense Example - William Blair Small-Mid Cap Growth Fund |
Dec. 31, 2025
USD ($)
|
|---|---|
| Class N | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | $ 126 |
| Expense Example, with Redemption, 3 Years | 421 |
| Expense Example, with Redemption, 5 Years | 738 |
| Expense Example, with Redemption, 10 Years | 1,635 |
| Class I | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | 101 |
| Expense Example, with Redemption, 3 Years | 343 |
| Expense Example, with Redemption, 5 Years | 604 |
| Expense Example, with Redemption, 10 Years | 1,352 |
| Class R6 | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | 96 |
| Expense Example, with Redemption, 3 Years | 310 |
| Expense Example, with Redemption, 5 Years | 542 |
| Expense Example, with Redemption, 10 Years | $ 1,208 |