S000008596 [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 Emerging Markets Growth Fund | Class N | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 24.84% | 10.40% | 9.99% | (33.33%) | 2.97% | 40.43% | 27.89% | (21.61%) | 48.53% | 1.49% |