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Regulatory Matters (Tables) | 9 Months Ended
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Sep. 30, 2025
Regulatory Assets and Liabilities Disclosure [Abstract] |
Schedule of Regulatory Assets and Liabilities | The following presents our current and long-term regulatory assets and liabilities as of September 30, 2025 and December 31, 2024 and the period we expect to recover or refund such amounts:
| Period of |  | September 30, 2025 |  | December 31, 2024
(in thousands) | Recovery/Refund |  | Current |  | Long-Term |  | Current |  | Long-Term
Regulatory Assets |  |  |  |  |  |  |  |  |
Pension and Other Postretirement Benefit Plans 1 | Various |  | $ | — |  |  | $ | 87,182 |  |  | $ | — |  |  | $ | 88,161 |
Alternative Revenue Program Riders 2 | Up to 2 years |  | 4,610 |  |  | 146 |  |  | 4,257 |  |  | 195 |
Deferred Income Taxes 1 | Asset lives |  | — |  |  | 9,070 |  |  | — |  |  | 8,944 |
Fuel Clause Adjustments 1 | Up to 1 year |  | 3,229 |  |  | — |  |  | 2,218 |  |  | — |
Derivative Instruments 1 | Up to 2 years |  | 795 |  |  | 512 |  |  | 1,989 |  |  | — |
Other 1 | Various |  | 799 |  |  | 1,026 |  |  | 1,498 |  |  | 1,373 |
Total Regulatory Assets |  |  | $ | 9,433 |  |  | $ | 97,936 |  |  | $ | 9,962 |  |  | $ | 98,673 |
Regulatory Liabilities |  |  |  |  |  |  |  |  |
Deferred Income Taxes | Asset lives |  | $ | — |  |  | $ | 124,832 |  |  | $ | — |  |  | $ | 130,387 |
Plant Removal Obligations | Asset lives |  | — |  |  | 132,438 |  |  | — |  |  | 126,263 |
Fuel Clause Adjustments | Up to 1 year |  | 5,197 |  |  | — |  |  | 11,432 |  |  | — |
Alternative Revenue Program Riders | Up to 1 year |  | 10,888 |  |  | — |  |  | 14,255 |  |  | — |
North Dakota PTC Refunds | Asset lives |  | — |  |  | 26,348 |  |  | — |  |  | 20,099 |
Pension and Other Postretirement Benefit Plans | Various |  | 2,547 |  |  | 10,350 |  |  | 2,547 |  |  | 10,758 |
Other | Various |  | 3,121 |  |  | 2,248 |  |  | 1,073 |  |  | 1,421 |
Total Regulatory Liabilities |  |  | $ | 21,753 |  |  | $ | 296,216 |  |  | $ | 29,307 |  |  | $ | 288,928 |
1 Costs subject to recovery without a rate of return. |  |  |  |  |  |  |  |  |
2 Amounts eligible for recovery includes an incentive or rate of return. |  |  |  |  |  |  |  |

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