Inventories Textual (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 ft3	Sep. 30, 2012 ft3	Dec. 31, 2011 ft3
Inventory, Net [Abstract]
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet)	9,100,000,000	11,400,000,000	10,800,000,000
Carrying value of gas storage inventories released under SCAAs with non-affiliates	$ 27,251	$ 32,627	$ 50,912
SCAAs [Member]
Public Utilities, Inventory [Line Items]
Number of storage agreements (in storage agreements)	3
SCAAs [Member] | Other current liabilities [Member]
Inventory, Net [Abstract]
Security Deposit Liability	$ 16,500	$ 22,500	$ 22,500
Expires in October 2015 [Member] | SCAAs [Member]
Public Utilities, Inventory [Line Items]
Number of storage agreements (in storage agreements)	2
Expires in October 2013 [Member] | SCAAs [Member]
Public Utilities, Inventory [Line Items]
Number of storage agreements (in storage agreements)	1