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Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 21,770	$ 27,342
Regulatory assets, long-term	124,413	125,508
Regulatory liabilities, current	27,211	24,844
Regulatory liabilities, long -term	233,989	234,430
Deferred Income Taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	0	0
Regulatory liabilities, long -term	128,042	129,437
Plant Removal Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	8,561	8,306
Regulatory liabilities, long -term	101,850	101,595
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	5,386	1,554
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	$ 6,215	5,772
Regulatory liabilities, long -term	3,986	3,336
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	2,603	2,603
Regulatory liabilities, long -term	$ 0	0
Regulatory Liabilities - Remaining Recovery/Refund Period	1 year
Derivative Instruments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 4,179	6,214
Regulatory liabilities, long -term	0	0
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	267	395
Regulatory liabilities, long -term	111	62
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	7,791	7,791
Regulatory assets, long-term	113,663	114,961
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	9,280	11,889
Regulatory assets, long-term	$ 5,713	5,564
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	1,098	742
ISO Cost Recovery Trackers
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	220	0
Regulatory assets, long-term	$ 950	1,342
Regulatory Assets - Remaining Recovery/Refund Period	2 years
Unrecovered Project Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 1,086	2,136
Regulatory assets, long-term	$ 1,456	1,455
Regulatory Assets - Remaining Recovery/Refund Period	5 years
Deferred Rate Case Expenses
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 542	607
Regulatory assets, long-term	1,037	1,131
Debt Reacquisition Premiums
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	68	100
Regulatory assets, long-term	$ 234	240
Regulatory Assets - Remaining Recovery/Refund Period	11 years
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 2,767	4,819
Regulatory assets, long-term	0	0
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	16	0
Regulatory assets, long-term	$ 262	$ 73

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Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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