Contingent Liabilities and Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Jul. 01, 2020	Dec. 31, 2019
Other Commitments [Abstract]
Commitments for construction and acquisition of property, plant, and equipment	$ 14,000
Reserve for rate refunds	0	$ 284,300	$ 188,842
Environmental assessment and remediation
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	2,400		2,500
Accrued environmental assessment and remediation costs, current	700		1,200
Accrued environmental assessment and remediation costs, noncurrent	1,700		$ 1,300
Potentially responsible party at various Superfund and state waste disposal sites
Site Contingency [Line Items]
Environmental assessment and remediation costs, best estimate	$ 500