BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 3,004,783		$ 2,770,005		$ 2,649,444
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,094,940		2,005,520		1,942,691
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	253,663		223,247		80,234
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	468,096		347,406		400,882
Midstream [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	153,536		157,779		159,940
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,970,235		2,733,952		2,583,747
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	85,293		73,298		87,066
Intercompany Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (50,745)	[1]	$ (37,245)	[1]	$ (21,369)	[1]

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