REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,095,166	$ 4,372,985
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	5,167,642	4,460,434
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,190,229	3,064,309
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	944,740	864,323
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	381,367	290,847
Operating Segments | Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	651,306	240,955
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	110,562	104,411
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (183,038)	$ (191,860)