Income Taxes (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Tax Cuts and Jobs Act of 2017, reduction of net deferred income tax liabilities			$ 223,660
Tax Cuts and Jobs Act of 2017, reduction of income tax expense		$ 1,131		$ 9,254
Tax Cuts and Jobs Act of 2017, change in tax rate, provisional unrecognized deferred tax liability			$ 216,098
Increase in regulatory liabilities, excess deferred income taxes				87,803
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		782		24,051
PUC temporary rates order, reduction in revenue	$ (1,353)	$ (22,745)		(24,098)	$ 0
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Federal statutory income tax rate						24.50%
Income Tax Benefits [Member]
Operating Loss Carryforwards [Line Items]
PUC temporary rates order, reduction in revenue				(17,135)
Future Amortization Of Regulatory Liabilities [Member]
Operating Loss Carryforwards [Line Items]
PUC temporary rates order, reduction in revenue				$ (6,963)