Inventories (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2015 USD ($) agreement Bcf	Sep. 30, 2014 USD ($) Bcf	Jun. 30, 2014 USD ($) Bcf
Public Utilities, Inventory
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet) | Bcf	4.5	11.6	6.1
Carrying value of gas storage inventories released under SCAAs with non-affiliates | $	$ 11,337	$ 49,897	$ 28,299
SCAAs
Public Utilities, Inventory
Number of storage agreements (in storage agreements)	3
Term of agreements	3 years
Number of storage agreements with Energy Services	2
Number of storage agreements with non-affiliates	1
SCAAs | Other Current Liabilities
Public Utilities, Inventory
Security deposit liability | $	$ 17,700	$ 17,600	$ 17,600