Related Party Transaction - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended					3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2012 Membership Interest Purchase Agreement
Related Party Transaction [Line Items]
Percentage Of Cash Distributed To Parent						50.00%
Percentage Of Cash Distributed To Partners Through Dilution						25.00%
Sales to Inergy	$ 11.8	$ 4.0	[1]	$ 0.5	[1]
Increased in net income by sales relate to storage space leased	$ 7.8	$ 1.3		$ 0.5

[1] Retrospectively adjusted as described in Note 1.