Regulatory liabilities (Details 2) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 44,395	$ 26,440	$ 31,186
Regulatory liabilities	454,669	448,454	433,628
Total regulatory liabilities	499,064	474,894	464,814
Net regulatory position	$ 66,754	19,857	(16,508)
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 9,630	4,929	0
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 6,331	955	13,107
Conservation programs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 3,834	4,126	144
Cost Recovery Mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	2,926	1,977	2,550
Regulatory liabilities	$ 16,313	14,025	9,508
Cost Recovery Mechanisms \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Cost Recovery Mechanisms \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 19 years
Taxes refundable to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 1,513	3,937	3,470
Regulatory liabilities	$ 200,879	203,222	212,472
Taxes refundable to customers \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Taxes refundable to customers \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Over plant lives
Refundable Fuel and Electric Costs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Regulatory liabilities due within one year	$ 1,179	3,253	316
Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	18,982	7,263	11,599
Regulatory liabilities	$ 1,638	1,587	6,377
Other regulatory liabilities \| Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 1 year
Other regulatory liabilities \| Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 15 years
Plant removal and decommissioning costs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Over plant lives
Regulatory liabilities	$ 214,467	208,650	171,485
Accumulated Deferred ITC
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	Up to 19 years
Regulatory liabilities	$ 13,996	13,594	13,352
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of March 31, 2023	**
Regulatory liabilities	$ 7,376	$ 7,376	$ 20,434

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.

+ References

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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-Topic 980
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-Paragraph 1
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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.

+ References

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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