BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Sep. 30, 2012
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,991,195		$ 2,770,005
Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,062,913		2,005,520
Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	253,680		223,247
Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	497,941		347,406
Midstream Investments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	156,135		157,779
Categorized Business Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,970,669		2,733,952
Retail and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	86,920		73,298
Eliminations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (66,394)	[1]	$ (37,245)	[1]

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