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Regulatory Matters (Tables) | 9 Months Ended
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Sep. 30, 2023
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, 2023 and December 31, 2022 and the period we expect to recover or refund such amounts:
| Period of |  | September 30, 2023 |  | December 31, 2022
(in thousands) | Recovery/Refund |  | Current |  | Long-Term |  | Current |  | Long-Term
Regulatory Assets |  |  |  |  |  |  |  |  |
Pension and Other Postretirement Benefit Plans 1 | Various |  | $ | — |  |  | $ | 86,286 |  |  | $ | — |  |  | $ | 88,354 |
Alternative Revenue Program Riders 2 | Up to 2 years |  | 5,780 |  |  | 118 |  |  | 5,679 |  |  | 2,508 |
Asset Retirement Obligations 1 | Asset lives |  | — |  |  | — |  |  | — |  |  | 1,467 |
Deferred Income Taxes | Asset lives |  | — |  |  | 931 |  |  | — |  |  | — |
ISO Cost Recovery Trackers 1 | Up to 2 years |  | 144 |  |  | 260 |  |  | 575 |  |  | 314 |
Unrecovered Project Costs 1 | Up to 4 years |  | 349 |  |  | 962 |  |  | 320 |  |  | 990 |
Deferred Rate Case Expenses 1 | Up to 3 years |  | 377 |  |  | 471 |  |  | 377 |  |  | 754 |
Fuel Clause Adjustments 1 | Up to 1 year |  | 9,141 |  |  | — |  |  | 10,893 |  |  | — |
Derivative Instruments 1 | Up to 2 years |  | 1,225 |  |  | 228 |  |  | 7,130 |  |  | — |
Other 1 | Various |  | 25 |  |  | 235 |  |  | 25 |  |  | 268 |
Total Regulatory Assets |  |  | $ | 17,041 |  |  | $ | 89,491 |  |  | $ | 24,999 |  |  | $ | 94,655 |
Regulatory Liabilities |  |  |  |  |  |  |  |  |
Deferred Income Taxes | Asset lives |  | $ | — |  |  | $ | 128,886 |  |  | $ | — |  |  | $ | 131,480 |
Plant Removal Obligations | Asset lives |  | 8,456 |  |  | 117,359 |  |  | 8,509 |  |  | 105,733 |
Fuel Clause Adjustments | Up to 1 year |  | 12,217 |  |  | — |  |  | 365 |  |  | — |
Alternative Revenue Program Riders | Up to 1 year |  | 8,426 |  |  | — |  |  | 2,504 |  |  | — |
North Dakota PTC Refunds | Asset lives |  | — |  |  | 10,281 |  |  | — |  |  | 7,136 |
Pension and Other Postretirement Benefit Plans | Various |  | 2,279 |  |  | 19,026 |  |  | 5,589 |  |  | — |
Other | Various |  | 907 |  |  | 257 |  |  | 333 |  |  | 148 |
Total Regulatory Liabilities |  |  | $ | 32,285 |  |  | $ | 275,809 |  |  | $ | 17,300 |  |  | $ | 244,497 |
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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