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Regulatory assets (Details) - USD ($) $ in Thousands | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2022 | Dec. 31, 2021 | Mar. 31, 2021 | Feb. 28, 2021
Regulatory Assets |  |  |  |
Regulatory Assets, Current | $ 89,078 | $ 118,691 | $ 98,452 |
Regulatory Assets, Noncurrent | 359,228 | 357,851 | 379,917 |
Total regulatory assets | 448,306 | 476,542 | 478,369 |
Regulatory assets not earning a rate of return | 268,100 | 296,600 | 361,400 |
Natural gas costs recoverable through rate adjustments |  |  |  |
Regulatory Assets |  |  |  |
Regulatory Assets, Current | 66,132 | 86,371 | 76,782 |
Regulatory Assets, Noncurrent | $ 3,246 | 5,186 | 15,158 |
Total regulatory assets |  |  |  | $ 44,000
Natural gas costs recoverable through rate adjustments | Minimum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 1 year |  |  |
Natural gas costs recoverable through rate adjustments | Maximum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 2 years |  |  |
Decoupling |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 1 year |  |  |
Regulatory Assets, Current | $ 7,609 | 9,131 | 4,180 |
Conservation programs |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 1 year |  |  |
Regulatory Assets, Current | $ 7,567 | 8,225 | 6,679 |
Cost recovery mechanisms |  |  |  |
Regulatory Assets |  |  |  |
Regulatory Assets, Current | 3,432 | 4,536 | 7,130 |
Regulatory Assets, Noncurrent | $ 67,989 | 44,870 | 15,508 |
Cost recovery mechanisms | Minimum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 1 year |  |  |
Cost recovery mechanisms | Maximum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 10 years |  |  |
Other regulatory assets |  |  |  |
Regulatory Assets |  |  |  |
Regulatory Assets, Current | $ 4,338 | 10,428 | 3,681 |
Regulatory Assets, Noncurrent | $ 10,318 | 9,742 | 6,509 |
Other regulatory assets | Minimum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 1 year |  |  |
Other regulatory assets | Maximum [Member] |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 17 years |  |  |
Pension and postretirement benefits |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | ** |  |  |
Regulatory Assets, Noncurrent | $ 142,681 | 142,681 | 155,924 |
Plant costs/asset retirement obligations |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Over plant lives |  |  |
Regulatory Assets, Noncurrent | $ 63,325 | 63,116 | 72,250 |
Plant retirement |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | - |  |  |
Regulatory Assets, Noncurrent | $ 29,452 | 50,070 | 73,498 |
Manufactured gas plant site remediation |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | - |  |  |
Regulatory Assets, Noncurrent | $ 26,089 | 26,053 | 26,002 |
Taxes recoverable from customers |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Over plant lives |  |  |
Regulatory Assets, Noncurrent | $ 12,492 | 12,339 | 10,800 |
Long-term debt refinancing costs |  |  |  |
Regulatory Assets |  |  |  |
Estimated Recovery or Refund Period as of March 31, 2022 | Up to 38 years |  |  |
Regulatory Assets, Noncurrent | $ 3,636 | $ 3,794 | $ 4,268 |

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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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- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + 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 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=123406419&loc=d3e44360-110383 + Details
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