BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		$ 4,143,664	$ 3,928,507	$ 3,718,570
Asset held for sale		206,905	0
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		4,166,993	3,922,001	3,696,982
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		2,663,054	2,519,578	2,517,401
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[1]	865,018	771,340	665,696
Asset held for sale		206,900
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		396,852	398,277	327,626
Operating Segments | Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		242,069	232,806	186,259
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		114,732	114,801	109,487
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[2]	$ (138,061)	$ (108,295)	$ (87,899)

[1] Includes assets held for sale of $206.9 million for September 30, 2018

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