REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 5,981,157	$ 5,722,278
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	6,121,333	5,850,079
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,861,240	3,707,461
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	937,696	914,788
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	393,744	365,423
Operating Segments | Storage and Transportation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	928,653	862,407
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	148,368	162,134
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (288,544)	$ (289,935)