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Regulatory assets (Details) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022 | Sep. 30, 2022
Regulatory Assets |  |  |
Regulatory Assets, Current | $ 169,248 | $ 165,092 | $ 148,160
Regulatory Assets, Noncurrent | 428,969 | 329,659 | 344,442
Total regulatory assets | 598,217 | 494,751 | 492,602
Regulatory assets not earning a rate of return | $ 211,800 | 242,500 | 264,400
Natural gas costs recoverable through rate adjustments |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 1 year |  |
Regulatory Assets, Current | $ 107,101 | 141,306 | 112,079
Regulatory Assets, Noncurrent | $ 64,914 | 0 | 462
Natural gas costs recoverable through rate adjustments | Maximum [Member] |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 2 years |  |
Conservation programs |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 1 year |  |
Regulatory Assets, Current | $ 14,411 | 8,544 | 9,363
Cost recovery mechanisms |  |  |
Regulatory Assets |  |  |
Regulatory Assets, Current | 9,461 | 4,019 | 3,354
Regulatory Assets, Noncurrent | $ 68,539 | 67,171 | 67,094
Cost recovery mechanisms | Minimum [Member] |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 1 year |  |
Cost recovery mechanisms | Maximum [Member] |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 10 years |  |
Other regulatory assets |  |  |
Regulatory Assets |  |  |
Regulatory Assets, Current | $ 20,500 | 8,567 | 21,036
Regulatory Assets, Noncurrent | $ 11,406 | 11,010 | 10,931
Other regulatory assets | Minimum [Member] |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 1 year |  |
Other regulatory assets | Maximum [Member] |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 16 years |  |
Pension and postretirement benefits |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | ** |  |
Regulatory Assets, Noncurrent | $ 144,448 | 143,349 | 137,582
Plant costs/asset retirement obligations |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Over plant lives |  |
Regulatory Assets, Noncurrent | $ 43,520 | 44,462 | 61,941
Manufactured gas plant site remediation |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | - |  |
Regulatory Assets, Noncurrent | $ 24,577 | 26,624 | 25,963
Plant to be retired |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | - |  |
Regulatory Assets, Noncurrent | $ 19,947 | 21,525 | 24,740
Environmental compliance programs |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | - |  |
Regulatory Assets, Noncurrent | $ 36,605 | 0 | 0
Taxes recoverable from customers |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Over plant lives |  |
Regulatory Assets, Noncurrent | $ 12,266 | 12,330 | 12,394
Long-term debt refinancing costs |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 37 years |  |
Regulatory Assets, Noncurrent | $ 2,747 | 3,188 | 3,335
Regulatory Asset, Electric Fuel & Purchased Power Deferral |  |  |
Regulatory Assets |  |  |
Estimated Recovery or Refund Period as of September 30, 2023 | Up to 1 year |  |
Regulatory Assets, Current | $ 17,775 | $ 2,656 | $ 2,328

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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 -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 + Details
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