Shareholder Report, Average Annual Return (Details) |
12 Months Ended | 60 Months Ended | 120 Months Ended |
|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2026 |
Jun. 30, 2026 |
|
| C000031584 | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Bruce Fund | ||
| Without Sales Load [Member] | C000031584 | |||
| Average Annual Return [Line Items] | |||
| Average Annual Return, Percent | 27.69% | 6.07% | 7.71% |
| S&P 500 Index TR | |||
| Average Annual Return [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 | ||
| Average Annual Return, Percent | 22.32% | 13.41% | 15.51% |