Goodwill Rollforward (Details) (USD $) In Thousands			12 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Natural Gas Distribution Segment [Member]	Sep. 30, 2011 Regulated Transmission and Storage Segment [Member]	Sep. 30, 2011 Nonregulated Segment [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 740,000	$ 739,314	$ 572,262	$ 132,341	$ 34,711
Goodwill Other Changes			646	40	0
Goodwill, Ending Balance	$ 740,000	$ 739,314	$ 572,908	$ 132,381	$ 34,711

Carrying amount as of the balance sheet date, which is the cumulative amount paid, adjusted for any amortization recognized prior to adoption of FAS 142 and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 43

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant