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