S000066499 [Member] Annual Total Returns |
12 Months Ended | |||||
|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
Dec. 31, 2020 |
|
| William Blair Small-Mid Cap Core Fund | Class I | ||||||
| Prospectus [Line Items] | ||||||
| Annual Return [Percent] | 1.27% | 12.04% | 13.26% | (17.11%) | 26.63% | 20.60% |