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Regulatory assets and liabilities Regulatory Liabilities (Details 2) - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019 | Mar. 31, 2019
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Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Current | $ 60,072 | $ 42,935 | $ 61,390
Regulatory Liability, Noncurrent | 443,205 | 447,370 | 457,084
Total regulatory liabilities | 503,277 | 490,305 | 518,474
Net regulatory position | (99,882) | (72,908) | (124,861)
Natural gas costs refundable through rate adjustments |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Current | 32,181 | 23,825 | 29,739
Taxes refundable to customers |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Current | 4,002 | 3,472 | 8,139
Regulatory Liability, Noncurrent | 240,148 | 246,034 | 259,638
Plant removal and decommissioning costs |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Noncurrent | 174,120 | 173,722 | 172,569
Pension and postretirement benefits |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Noncurrent | 18,040 | 18,065 | 15,239
Other Regulatory Liabilities |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liability, Current | 23,889 | 15,638 | 23,512
Regulatory Liability, Noncurrent | $ 10,897 | $ 9,549 | $ 9,638

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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 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 Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent 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 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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