Contingent Liabilities and Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Other Commitments [Abstract]
Commitments for construction and acquisition of property, plant, and equipment	$ 91,000
Reserve for rate refunds	188,842	$ 0
Environmental assessment and remediation
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	2,500	3,500
Accrued environmental assessment and remediation costs, current	1,200	1,500
Accrued environmental assessment and remediation costs, noncurrent	1,300	$ 2,000
Potentially responsible party at various Superfund and state waste disposal sites
Site Contingency [Line Items]
Environmental assessment and remediation costs, best estimate	$ 500