S000008594 [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 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| William Blair Growth Fund | Class N | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 10.19% | 21.81% | 37.76% | (29.65%) | 22.09% | 35.97% | 31.97% | 5.10% | 24.35% | (0.98%) |