BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Sep. 30, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,669,739		$ 2,649,444
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,622,957		2,583,747
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,951,497		1,942,691
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	346,995		400,882
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	166,478		80,234
Energy Holdings [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	157,987		159,940
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	66,742		87,066
Business Intersegment, Eliminations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (19,960)	[1]	$ (21,369)	[1]

[1] Consists of transactions between subsidiaries that are eliminated and reclassified in consolidation.