S000008602 [Member] Expense Example - William Blair Small 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 | 425 |
| Expense Example, with Redemption, 5 Years | 746 |
| Expense Example, with Redemption, 10 Years | 1,656 |
| 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 | 315 |
| Expense Example, with Redemption, 5 Years | 551 |
| Expense Example, with Redemption, 10 Years | $ 1,230 |