BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Sep. 30, 2012
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,941,658		$ 2,770,005
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,048,349		2,005,520
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	243,616		223,247
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	466,565		347,406
Energy Holdings [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	155,908		157,779
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,914,438		2,733,952
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	71,293		73,298
Intercompany assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (44,073)	[1]	$ (37,245)	[1]

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