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Regulatory assets (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2021 | Feb. 28, 2021 | Dec. 31, 2020
Regulatory Assets [Line Items] |  |  |
Current regulatory assets | $ 118,691 |  | $ 68,527
Regulatory assets | 357,851 |  | 379,381
Total regulatory assets | 476,542 |  | 447,908
Regulatory assets not earning a rate of return | 296,600 |  | 332,500
Natural gas costs recoverable through rate adjustments |  |  |
Regulatory Assets [Line Items] |  |  |
Current regulatory assets | 86,371 |  | 42,481
Regulatory assets | $ 5,186 |  | 21,539
Total regulatory assets |  | $ 44,000 |
Natural gas costs recoverable through rate adjustments | Minimum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 1 year |  |
Natural gas costs recoverable through rate adjustments | Maximum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 2 years |  |
Decoupling |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 1 year |  |
Current regulatory assets | $ 9,131 |  | 703
Conservation programs |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 1 year |  |
Current regulatory assets | $ 8,225 |  | 7,117
Cost recovery mechanisms |  |  |
Regulatory Assets [Line Items] |  |  |
Current regulatory assets | 4,536 |  | 10,645
Regulatory assets | $ 44,870 |  | 16,245
Cost recovery mechanisms | Minimum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 1 year |  |
Cost recovery mechanisms | Maximum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 10 years |  |
Other regulatory assets |  |  |
Regulatory Assets [Line Items] |  |  |
Current regulatory assets | $ 10,428 |  | 7,581
Regulatory assets | $ 9,742 |  | 6,356
Other regulatory assets | Minimum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 1 year |  |
Other regulatory assets | Maximum |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 17 years |  |
Pension and postretirement benefits |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | ** |  |
Regulatory assets | $ 142,681 |  | 155,942
Plant costs/asset retirement obligation costs |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Over plant lives |  |
Regulatory assets | $ 63,116 |  | 71,740
Plants to be retired |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | - |  |
Regulatory assets | $ 50,070 |  | 65,919
Manufactured gas plant sites remediation |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | - |  |
Regulatory assets | $ 26,053 |  | 26,429
Taxes recoverable from customers |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Over plant lives |  |
Regulatory assets | $ 12,339 |  | 10,785
Long-term debt refinancing costs |  |  |
Regulatory Assets [Line Items] |  |  |
Regulatory asset, recovery period | Up to 39 years |  |
Regulatory assets | $ 3,794 |  | $ 4,426

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- Definition 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 -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 40 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499898&loc=d3e44174-110380 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123417213&loc=d3e43603-110378 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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