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Regulatory liabilities (Details 2) - USD ($) $ in Thousands | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020 | Jun. 30, 2020
Regulatory Liabilities [Line Items] |  |  |
Regulatory liabilities due within one year | $ 23,454 | $ 31,450 | $ 48,000
Regulatory liabilities | 428,467 | 428,075 | 438,652
Total regulatory liabilities | 451,921 | 459,525 | 486,652
Net regulatory position | $ 34,573 | (11,617) | (75,070)
Natural gas costs refundable through rate adjustments |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Up to 1 year |  |
Regulatory liabilities due within one year | $ 8,935 | 18,565 | 29,557
Electric fuel and purchased power deferral |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Up to 1 year |  |
Regulatory liabilities due within one year | $ 5,431 | 3,667 | 7,799
Deferred Income Tax Charge [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory liabilities due within one year | 3,434 | 3,557 | 4,012
Regulatory liabilities | $ 222,098 | 227,850 | 236,142
Deferred Income Tax Charge [Member] | Minimum [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Up to 1 year |  |
Deferred Income Tax Charge [Member] | Maximum [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Over plant lives |  |
Other Regulatory Liabilities |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory liabilities due within one year | $ 5,654 | 5,661 | 6,632
Regulatory liabilities | $ 18,048 | 16,065 | 11,096
Other Regulatory Liabilities | Minimum [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Up to 1 year |  |
Other Regulatory Liabilities | Maximum [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Up to 21 years |  |
Plant retirement |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | Over plant lives |  |
Regulatory liabilities | $ 171,381 | 167,171 | 173,399
Pension and postretirement benefits |  |  |
Regulatory Liabilities [Line Items] |  |  |
Estimated Recovery or Refund Period as of June 30, 2021 | ** |  |
Regulatory liabilities | $ 16,940 | $ 16,989 | $ 18,015

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- Definition The net amount of all regulatory assets less all regulatory liabilities as of the end of the period. + 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 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=121557228&loc=d3e43603-110378 + Details
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- Definition 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 -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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