Inventories (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2016 USD ($) agreement Bcf	Sep. 30, 2015 USD ($) Bcf	Jun. 30, 2015 USD ($) Bcf
Public Utilities, Inventory
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet) | Bcf	4.6	9.0	4.5
Carrying value of gas storage inventories released under SCAAs with non-affiliates | $	$ 8,390	$ 22,694	$ 11,337
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