REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,198,985	$ 852,105	$ 833,677
Revenues out of scope	1,706,994	1,304,508	1,119,991
Total operating revenues	2,905,979	2,156,613	1,953,668
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	654,886	549,026	549,333
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	446,471	219,981	208,665
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	92,531	79,256	69,357
Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,097	3,842	6,322
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	2,854,054	2,106,511	1,907,687
Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0
Total operating revenues	55,818	51,444	49,810
Home Services and Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	55,629	50,689	48,867
Home Services and Other | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	189	755	943
Home Services and Other | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Home Services and Other | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	950,276	694,635	695,858
Revenues out of scope	177,141	37,161	34,065
Total operating revenues	1,127,417	731,796	729,923
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	586,678	487,018	490,233
Natural Gas Distribution | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	265,970	124,519	129,946
Natural Gas Distribution | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	92,531	79,256	69,357
Natural Gas Distribution | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,097	3,842	6,322
Clean Energy Ventures | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	43,804	29,841	21,483
Revenues out of scope	84,476	65,434	81,134
Total operating revenues	128,280	95,275	102,617
Clean Energy Ventures | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,579	11,319	10,233
Clean Energy Ventures | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,225	18,522	11,250
Clean Energy Ventures | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Clean Energy Ventures | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Energy Services
Disaggregation of Revenue [Line Items]
Total operating revenues	53,000
Energy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	83,801	26,933	24,511
Revenues out of scope	1,445,377	1,201,913	1,004,792
Total operating revenues	1,529,178	1,228,846	1,029,303
Energy Services | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Energy Services | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	83,801	26,933	24,511
Energy Services | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Energy Services | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Storage and Transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	65,286	49,252	42,015
Revenues out of scope	0	0	0
Total operating revenues	65,286	49,252	42,015
Storage and Transportation | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Storage and Transportation | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	65,286	49,252	42,015
Storage and Transportation | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Storage and Transportation | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0	$ 0