REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,155,199	$ 4,372,985
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	5,230,423	4,460,434
Operating Segments | Natural Gas Distribution
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,243,556	3,064,309
Operating Segments | Clean Energy Ventures
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	969,545	864,323
Operating Segments | Energy Services
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	208,562	290,847
Operating Segments | Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	808,760	240,955
Home Services and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	134,113	104,411
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (209,337)	$ (191,860)