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Regulatory assets and liabilities (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019
Regulatory assets and liabilities |  |
Current regulatory assets | $ 68,527 | $ 63,613
Regulatory assets | 379,381 | 353,784
Regulatory assets: | 447,908 | 417,397
Regulatory liabilities due within one year | 31,450 | 42,935
Regulatory liabilities | 428,075 | 447,370
Regulatory liabilities: | 459,525 | 490,305
Net regulatory position | (11,617) | (72,908)
Regulatory assets not earning a rate of return | $ 332,500 | 276,500
Natural gas costs refundable through rate adjustments |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Regulatory liabilities due within one year | $ 18,565 | 23,825
Liabilities Electric fuel and purchased power deferral |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Regulatory liabilities due within one year | $ 3,667 | 5,824
Taxes recoverable from/refundable to customers |  |
Regulatory assets and liabilities |  |
Regulatory liabilities due within one year | 3,557 | 3,472
Regulatory liabilities | $ 227,850 | 246,034
Taxes recoverable from/refundable to customers | Minimum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Taxes recoverable from/refundable to customers | Maximum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Over plant lives |
Plants to be retired |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Over plant lives |
Regulatory liabilities | $ 167,171 | 173,722
Pension and postretirement benefits |  |
Regulatory assets and liabilities |  |
Estimated recovery period | ** |
Regulatory liabilities | $ 16,989 | 18,065
Other regulatory assets/liabilities |  |
Regulatory assets and liabilities |  |
Regulatory liabilities due within one year | 5,661 | 9,814
Regulatory liabilities | $ 16,065 | 9,549
Other regulatory assets/liabilities | Minimum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Other regulatory assets/liabilities | Maximum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 21 years |
Natural gas costs recoverable through rate adjustments |  |
Regulatory assets and liabilities |  |
Current regulatory assets | $ 42,481 | 42,823
Regulatory assets | $ 21,539 | 46,381
Natural gas costs recoverable through rate adjustments | Minimum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Natural gas costs recoverable through rate adjustments | Maximum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 2 years |
Cost recovery mechanisms |  |
Regulatory assets and liabilities |  |
Current regulatory assets | $ 10,645 | 6,288
Regulatory assets | $ 16,245 | 13,108
Cost recovery mechanisms | Minimum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Cost recovery mechanisms | Maximum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 10 years |
Conservation programs |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Current regulatory assets | $ 7,117 | 6,963
Pension and postretirement benefits |  |
Regulatory assets and liabilities |  |
Estimated recovery period | ** |
Regulatory assets | $ 155,942 | 157,069
Asset retirement obligation costs |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Over plant lives |
Regulatory assets | $ 71,740 | 66,000
Plants to be retired |  |
Regulatory assets and liabilities |  |
Estimated recovery period | - |
Regulatory assets | $ 65,919 | 32,931
Manufactured gas plant sites remediation |  |
Regulatory assets and liabilities |  |
Estimated recovery period | - |
Regulatory assets | $ 26,429 | 15,126
Taxes recoverable from/refundable to customers |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Over plant lives |
Regulatory assets | $ 10,785 | 11,486
Long-term debt refinancing costs |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 40 years |
Regulatory assets | $ 4,426 | 4,286
Other regulatory assets/liabilities |  |
Regulatory assets and liabilities |  |
Current regulatory assets | 8,284 | 7,539
Regulatory assets | $ 6,356 | $ 7,397
Other regulatory assets/liabilities | Minimum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 1 year |
Other regulatory assets/liabilities | Maximum |  |
Regulatory assets and liabilities |  |
Estimated recovery period | Up to 18 years |

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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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