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Regulatory Matters - Summary of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 16,127	$ 24,999
Regulatory assets, long-term	95,715	94,655
Regulatory liabilities, current	25,408	17,300
Regulatory liabilities, long -term	276,547	244,497
Deferred Income Taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	0	0
Regulatory liabilities, long -term	136,022	131,480
Plant Removal Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	0	8,509
Regulatory liabilities, long -term	117,030	105,733
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	11,350	365
Regulatory liabilities, long -term	$ 0	0
Regulatory liabilities - remaining recovery/refund period	1 year
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 6,885	2,504
Regulatory liabilities, long -term	$ 0	0
Regulatory liabilities - remaining recovery/refund period	1 year
North Dakota PTC Refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 0	0
Regulatory liabilities, long -term	12,011	7,136
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	6,138	5,589
Regulatory liabilities, long -term	11,307	0
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	1,035	333
Regulatory liabilities, long -term	177	148
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	154	0
Regulatory assets, long-term	86,134	88,354
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	3,719	5,679
Regulatory assets, long-term	$ 158	2,508
Regulatory assets - Remaining recovery/refund period	2 years
Asset Retirement Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 0	0
Regulatory assets, long-term	87	1,467
Deferred Income Taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	0	0
Regulatory assets, long-term	6,940	0
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	7,294	10,893
Regulatory assets, long-term	$ 0	0
Regulatory assets - Remaining recovery/refund period	1 year
Derivative Instruments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 4,210	7,130
Regulatory assets, long-term	$ 0	0
Regulatory assets - Remaining recovery/refund period	1 year
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 750	1,297
Regulatory assets, long-term	$ 2,396	$ 2,326

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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