Other Operating Income (Expense), Net (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Component of Operating Income [Abstract]
Non-tariff service income	$ 2,830	$ 1,491	$ 2,633
Environmental matters	0	6,155	(2,918)
Net interest on PGC overcollections	(1,403)	(130)	(1,740)
Other, net	837	813	25
Total other operating income (expense), net	$ 2,264	$ 8,329	$ (2,000)

The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration