REVENUE - DISAGGREGATED REVENUE - PRODUCT (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
Alternative revenue programs	11,259	(7,282)	15,750
Derivative instruments	1,695,829	1,311,364	1,105,357
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
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	951,626	694,635	695,858
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	151,536	77,953	69,239
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	33,932	33,250	32,455
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,250	18,979	18,562
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,487	4,571	1,384
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	38,317	25,270	20,099
Energy Services
Disaggregation of Revenue [Line Items]
Total operating revenues	53,000
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	2,854,054	2,106,511	1,907,687
Operating Segments | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	950,276	694,635	695,858
Alternative revenue programs	11,259	(7,282)	15,750
Derivative instruments	165,882	44,443	18,315
Revenues out of scope	177,141	37,161	34,065
Total operating revenues	1,127,417	731,796	729,923
Operating Segments | Natural Gas Distribution | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	951,626	694,635	695,858
Operating Segments | Natural Gas Distribution | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Natural Gas Distribution | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Natural Gas Distribution | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Natural Gas Distribution | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Natural Gas Distribution | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Clean Energy Ventures
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	43,804	29,841	21,483
Alternative revenue programs	0	0	0
Derivative instruments	84,476	65,434	81,134
Revenues out of scope	84,476	65,434	81,134
Total operating revenues	128,280	95,275	102,617
Operating Segments | Clean Energy Ventures | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Clean Energy Ventures | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Clean Energy Ventures | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Clean Energy Ventures | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Clean Energy Ventures | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,487	4,571	1,384
Operating Segments | Clean Energy Ventures | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	38,317	25,270	20,099
Operating Segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	83,801	26,933	24,511
Alternative revenue programs	0	0	0
Derivative instruments	1,445,471	1,201,487	1,005,908
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
Operating Segments | Energy Services | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Energy Services | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	83,801	26,933	24,511
Operating Segments | Energy Services | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Energy Services | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Energy Services | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Energy Services | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Storage and Transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	65,286	49,252	42,015
Alternative revenue programs	0	0	0
Derivative instruments	0	0	0
Revenues out of scope	0	0	0
Total operating revenues	65,286	49,252	42,015
Operating Segments | Storage and Transportation | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Storage and Transportation | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	67,735	51,020	44,728
Operating Segments | Storage and Transportation | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Storage and Transportation | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Storage and Transportation | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | Storage and Transportation | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
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 | Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	55,818	51,444	49,810
Alternative revenue programs	0	0	0
Derivative instruments	0	0	0
Revenues out of scope	0	0	0
Total operating revenues	55,818	51,444	49,810
Home Services and Other | Home Services and Other | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Home Services and Other | Home Services and Other | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Home Services and Other | Home Services and Other | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	33,932	33,250	32,455
Home Services and Other | Home Services and Other | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,250	18,979	18,562
Home Services and Other | Home Services and Other | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Home Services and Other | Home Services and Other | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(4,163)	(2,553)	(3,920)
Revenues out of scope	(94)	426	(1,116)
Eliminations | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,350)	0	0
Revenues out of scope	0	0	0
Eliminations | Clean Energy Ventures
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Revenues out of scope	0	0	0
Eliminations | Energy Services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Revenues out of scope	(94)	426	(1,116)
Eliminations | Storage and Transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(2,449)	(1,768)	(2,713)
Revenues out of scope	0	0	0
Eliminations | Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(364)	(785)	(1,207)
Revenues out of scope	$ 0	$ 0	$ 0