S000034349 [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 Small Cap Growth Fund | Class N | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 13.68% | 8.09% | 21.93% | (28.12%) | 15.23% | 32.26% | 20.34% | (23.57%) | 40.09% | (5.33%) |