Contingent Liabilities and Commitments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Reserve for rate refund	$ 248,300
Environmental assessment and remediation [Member]
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	2,500	$ 2,500
Accrued environmental assessment and remediation costs, current	1,200	1,200
Accrued environmental assessment and remediation costs, noncurrent	1,300	$ 1,300
Potentially responsible party at various Superfund and state waste disposal sites [Member] | Maximum [Member]
Site Contingency [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate	$ 500