Inventories - Narrative (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014 ft3 Storage_Agreement	Sep. 30, 2013 ft3
Inventory [Line Items]
Number of Storage Agreements	4
Volume of gas storage inventories released under SCAAs with non-affiliates (in cubic feet)	200,000,000	600,000,000
Carrying value of gas storage inventories released under SCAAs with non-affiliates	$ 0.8	$ 2.4
Minimum
Inventory [Line Items]
SCAA Contract Term, in years	1 year
Maximum
Inventory [Line Items]
SCAA Contract Term, in years	3 years