REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,282,084	$ 4,372,985
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	5,366,756	4,460,434
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,319,754	3,064,309
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,007,240	864,323
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	225,830	290,847
Operating Segments | Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	813,932	240,955
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	133,773	104,411
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (218,445)	$ (191,860)