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Income Taxes - Summary of Significant Factors Impact on Difference Between Effective Tax Rate and Federal Statutory Rate (Parenthetical) (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Regulatory liabilities |  | $ 75,559 |  | $ 75,559 |  | $ 46,435
Non-plant excess deferred turnaround, amount |  | $ 0 | $ 0 | $ 0 | $ 8,476 |
WUTC [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Non-plant excess deferred turnaround, amount | $ 8,400 |  |  |  |  |
WUTC [Member] | Income Tax Related [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Regulatory liabilities | $ 10,900 |  |  |  |  |

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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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