BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,770,005		$ 2,649,444		$ 2,563,133
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,005,520		1,942,691		1,904,545
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	223,247		80,234		645
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	347,406		400,882		432,380
Midstream Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	157,779		159,940		159,882
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,733,952		2,583,747		2,497,452
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	73,298		87,066		85,219
Business Intersegment, Eliminations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (37,245)	[1]	$ (21,369)	[1]	$ (19,538)	[1]

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