Other Operating (Expense) Income, Net - Schedule of Other Income, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Component of Operating Income [Abstract]
Non-tariff service income	$ 2,633	$ 4,760	$ 2,670
Environmental matters	(2,918)	1,152	297
Construction service income	0	2,175	0
Sale of HVAC Business	0	1,065	0
PGC interest on over (under) collection	(1,740)	(606)	1,388
Other, net	25	323	4
Total other operating (expense) income, net	$ (2,000)	$ 8,869	$ 4,359