Summary of Significant Accounting Policies - Summary of Concentration of Investments (Details) - EBP 004 - USD ($) |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Fidelity 500 Index Fund | ||
| EBP, Accounting Standard Update and Change in Accounting Principle [Line Items] | ||
| Amount | $ 126,720,830 | |
| Percent of net assets | 15.00% | |
| MDU Resources Common Stock | ||
| EBP, Accounting Standard Update and Change in Accounting Principle [Line Items] | ||
| Amount | $ 105,308,075 | $ 87,182,528 |
| Percent of net assets | 12.00% | 11.00% |
| T Rowe Price Large-Cap Growth Fund | ||
| EBP, Accounting Standard Update and Change in Accounting Principle [Line Items] | ||
| Amount | $ 104,311,674 | $ 84,015,967 |
| Percent of net assets | 12.00% | 11.00% |
| Vanguard Institutional Index Fund | ||
| EBP, Accounting Standard Update and Change in Accounting Principle [Line Items] | ||
| Amount | $ 100,144,746 | |
| Percent of net assets | 13.00% |