REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,569,802	$ 4,372,985	$ 4,143,664
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	5,636,185	4,460,434	4,166,993
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,531,477	3,064,309	2,663,054
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,015,073	864,323	865,018
Asset held for sale			206,900
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	244,836	290,847	396,852
Operating Segments | Storage and Transportation
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	844,799	240,955	242,069
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	138,375	104,411	114,732
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (204,758)	$ (191,860)	$ (138,061)