REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Sep. 30, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		$ 4,089,973	$ 4,143,664
Assets held for sale		0	206,905
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		4,050,416	4,166,993
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		2,790,221	2,663,054
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[1]	721,162	865,018
Assets held for sale			206,900
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		320,476	396,852
Operating Segments | Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		218,557	242,069
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets		195,381	114,732
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	[2]	$ (155,824)	$ (138,061)

[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.