S000008601 [Member] Expense Example - William Blair Large Cap Growth Fund |
Dec. 31, 2025
USD ($)
|
|---|---|
| Class N | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | $ 92 |
| Expense Example, with Redemption, 3 Years | 313 |
| Expense Example, with Redemption, 5 Years | 552 |
| Expense Example, with Redemption, 10 Years | 1,237 |
| Class I | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | 66 |
| Expense Example, with Redemption, 3 Years | 230 |
| Expense Example, with Redemption, 5 Years | 407 |
| Expense Example, with Redemption, 10 Years | 921 |
| Class R6 | |
| Prospectus [Line Items] | |
| Expense Example, with Redemption, 1 Year | 61 |
| Expense Example, with Redemption, 3 Years | 201 |
| Expense Example, with Redemption, 5 Years | 353 |
| Expense Example, with Redemption, 10 Years | $ 795 |