Inventories (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Mar. 31, 2015 agreement	Sep. 30, 2014 Bcf	Mar. 31, 2014 Bcf
Public Utilities, Inventory
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet)	1.0	11.6	1.3
Carrying value of gas storage inventories released under SCAAs with non-affiliates	4,082	$ 49,897	$ 5,421
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