S000008597 [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 Small Cap Value Fund | Class I | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 2.91% | 3.44% | 10.86% | (11.12%) | 29.49% | 2.80% | 26.16% | (13.96%) | 13.13% | 31.36% |