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.