Inventories (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2016 USD ($) agreement Bcf	Sep. 30, 2015 USD ($) Bcf	Mar. 31, 2015 USD ($) Bcf
Public Utilities, Inventory
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet) | Bcf	1.1	9.0	1.0
Carrying value of gas storage inventories released under SCAAs with non-affiliates | $	$ 2,593	$ 22,694	$ 4,082
SCAAs
Public Utilities, Inventory
Number of storage agreements	2
Term of agreements (in years)	3 years
Number of storage agreements with Energy Services	1
Number of storage agreements with non-affiliates	1
SCAAs | Other Current Liabilities
Public Utilities, Inventory
Security deposit liability | $	$ 15,100	$ 17,700	$ 17,700