Shareholder Report, Line Graph (Details) - USD ($) |
12 Months Ended | 24 Months Ended | 36 Months Ended | 48 Months Ended | 60 Months Ended | 72 Months Ended | 84 Months Ended | 96 Months Ended | 108 Months Ended | 120 Months Ended | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2016 |
Jun. 30, 2026 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2021 |
Jun. 30, 2022 |
Jun. 30, 2023 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2026 |
|
| C000031584 | ||||||||||||
| Account Value [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Bruce Fund | |||||||||||
| Accumulated Value | $ 10,000 | $ 10,374 | $ 10,789 | $ 11,740 | $ 12,088 | $ 15,644 | $ 14,900 | $ 14,772 | $ 15,262 | $ 16,452 | $ 21,008 | |
| S&P 500 Index TR | ||||||||||||
| Account Value [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | S&P 500<sup style="inset: 1.5px 0px 4px; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center; text-align-last: auto; white-space-collapse: preserve-breaks;">®</sup> Index | |||||||||||
| Accumulated Value | $ 10,000 | $ 11,790 | $ 13,484 | $ 14,889 | $ 16,006 | $ 22,536 | $ 20,144 | $ 24,091 | $ 30,006 | $ 34,556 | $ 42,271 | |