Regulatory liabilities (Details 2) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 48,057	$ 26,440	$ 17,884
Regulatory liabilities	455,877	448,454	433,019
Total regulatory liabilities	503,934	474,894	450,903
Net regulatory position	$ 34,413	19,857	(1,307)
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 17,820	955	738
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 8,481	4,929	4,161
Cost Recovery Mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	3,304	1,977	3,172
Regulatory liabilities	$ 18,226	14,025	10,898
Cost Recovery Mechanisms \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Cost Recovery Mechanisms \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 19 years
Conservation programs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 2,851	4,126	352
Taxes refundable to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	1,513	3,937	3,728
Regulatory liabilities	$ 197,757	203,222	209,022
Taxes refundable to customers \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Taxes refundable to customers \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Over plant lives
Refundable Fuel and Electric Costs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 103	3,253	1,092
Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	13,985	7,263	4,641
Regulatory liabilities	$ 1,694	1,587	6,649
Other regulatory liabilities \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 1 year
Other regulatory liabilities \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 15 years
Plant removal and decommissioning costs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Over plant lives
Regulatory liabilities	$ 216,682	208,650	172,755
Accumulated Deferred ITC
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	Up to 19 years
Regulatory liabilities	$ 14,398	13,594	14,009
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2023	**
Regulatory liabilities	$ 7,120	$ 7,376	$ 19,686

The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481878/980-340-50-1

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Describes the continual or periodic assessment of the probability of future recovery of regulatory assets.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-Publisher FASB
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