Amount of cash paid to acquire the entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph f(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_BusinessAcquisitionCostOfAcquiredEntityCashPaid
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

US Salt Acquisition - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	May 14, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Business Acquisition [Line Items]
Effective date of acquisition	May 14, 2012
US Salt, LLC
Business Acquisition [Line Items]
Purchase price paid in cash	$ 182.5
Shares issued to Inergy for partial consideration	473,707
Increase in net income		$ 7.8	$ 11.9	$ 11.8