S000001273 [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 |
|
| MID CAP INDEX FUND | MID CAP INDEX FUND | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 7.42% | 13.85% | 16.31% | (13.22%) | 24.63% | 13.55% | 25.93% | (11.20%) | 16.04% | 20.58% |