REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,722,278	$ 5,316,477	$ 4,157,942
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	5,850,079	5,435,389	4,290,550
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,707,461	3,531,477	3,064,309
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	914,788	814,277	694,439
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	365,423	244,836	290,847
Operating Segments | Storage and Transportation
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	862,407	844,799	240,955
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	162,134	138,375	104,411
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (289,935)	$ (257,287)	$ (237,019)