BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Sep. 30, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		$ 3,632,790	$ 3,284,357
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		3,614,479	3,252,206
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		2,485,738	2,305,293
Operating Segments [Member] | Energy Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		325,681	260,021
Operating Segments [Member] | Clean Energy Ventures [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		611,644	504,885
Operating Segments [Member] | Midstream [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		191,416	182,007
Home Services and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		106,351	88,880
Intercompany Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[1]	$ (88,040)	$ (56,729)

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