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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2024
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 December 31, 2024 and 2023 and the period we expect to recover or refund such amounts:
| Period of |  | 2024 |  | 2023
(in thousands) | Recovery/Refund |  | Current |  | Long-Term |  | Current |  | Long-Term
Regulatory Assets |  |  |  |  |  |  |  |  |
Pension and Other Postretirement Benefit Plans 1 | See below |  | $ | — |  |  | $ | 88,161 |  |  | $ | 154 |  |  | $ | 86,134 |
Alternative Revenue Program Riders 2 | Up to 2 years |  | 4,257 |  |  | 195 |  |  | 3,719 |  |  | 158 |
Deferred Income Taxes | Asset lives |  | — |  |  | 8,944 |  |  | — |  |  | 6,940 |
Fuel Clause Adjustments 1 | Up to 1 year |  | 2,218 |  |  | — |  |  | 7,294 |  |  | — |
Derivative Instruments 1 | Up to 1 year |  | 1,989 |  |  | — |  |  | 4,210 |  |  | — |
Other 1 | Various |  | 1,498 |  |  | 1,373 |  |  | 750 |  |  | 2,483 |
Total Regulatory Assets |  |  | 9,962 |  |  | 98,673 |  |  | 16,127 |  |  | 95,715 |
Regulatory Liabilities |  |  |  |  |  |  |  |  |
Deferred Income Taxes | Asset lives |  | — |  |  | 130,387 |  |  | — |  |  | 136,022 |
Plant Removal Obligations | Asset lives |  | — |  |  | 126,263 |  |  | — |  |  | 117,030 |
Fuel Clause Adjustments | Up to 1 year |  | 11,432 |  |  | — |  |  | 11,350 |  |  | — |
Alternative Revenue Program Riders | Up to 1 year |  | 14,255 |  |  | — |  |  | 6,885 |  |  | — |
North Dakota PTC Refunds | Asset lives |  | — |  |  | 20,099 |  |  | — |  |  | 12,011 |
Pension and Other Postretirement Benefit Plans | See below |  | 2,547 |  |  | 10,758 |  |  | 6,138 |  |  | 11,307 |
Other | Various |  | 1,073 |  |  | 1,421 |  |  | 1,035 |  |  | 177 |
Total Regulatory Liabilities |  |  | $ | 29,307 |  |  | $ | 288,928 |  |  | $ | 25,408 |  |  | $ | 276,547 |
1 Costs subject to recovery without a rate of return. |  |  |  |  |  |
2 Amount eligible for recovery includes an incentive or rate of return. |  |  |  |  |  |

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