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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 | 6 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |
Regulatory liabilities |  |  | $ 70,176 |  | $ 70,176 |  | $ 46,435
Non-plant excess deferred turnaround, amount |  |  | 0 | $ 8,390 | 0 | $ 8,476 |
Income Tax Related [Member] |  |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |
Regulatory liabilities | [1] |  | $ 45,431 |  | $ 45,431 |  | $ 14,952
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 |  |  |  |  |
[1] | In 2021, the Company received regulatory approval in all jurisdictions to change to flow-through tax treatment of certain basis adjustments, which was $127.5 million.

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