BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2009
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,649,444		$ 2,563,133		$ 2,321,030
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,583,747		2,497,452		2,278,306
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,942,691		1,904,545		1,797,165
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	400,882		432,380		327,532
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	80,234		645		0
Midstream Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	159,940		159,882		153,609
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	87,066		85,219		69,411
Business Intersegment, Eliminations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (21,369)	[1]	$ (19,538)	[1]	$ (26,687)	[1]

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