Details of Selected Consolidated Balance Sheet Captions - Deferred Charges and Other Assets Detail Table (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets from risk management activities	$ 250	$ 803
Total	294,018	220,636
Defined Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension Asset	26,972	(25,211)
Other Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Marketable securities	99,385	88,409
Regulatory assets	141,778	110,977
Assets from risk management activities	250	803
Taxes receivable	10,099	0
Other	15,534	20,447
Total	294,018	220,636
Other Assets \| Defined Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension Asset	$ 26,972	$ 0

Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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