REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 384,433	$ 432,643	$ 748,984	$ 716,733
Alternative revenue programs	27,270	2,504	23,805	13,158
Derivative instruments	232,501	478,745	603,365	863,299
Revenues out of scope	259,594	479,673	618,610	871,425
Total operating revenues	644,027	912,316	1,367,594	1,588,158
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	327,198	381,861	615,365	605,657
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,723	30,651	92,409	70,673
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,739	8,492	17,400	16,959
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,709	4,730	10,314	10,214
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,085	1,019	3,287	1,865
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,084	6,846	13,788	13,316
Energy Services
Disaggregation of Revenue [Line Items]
Total operating revenues	9,500	10,300	29,500	32,400
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	632,861	901,626	1,352,019	1,567,968
Operating Segments | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	326,860	381,523	614,690	604,982
Alternative revenue programs	27,270	2,504	23,805	13,158
Derivative instruments	46,370	79,447	119,414	119,769
Revenues out of scope	73,640	81,951	143,219	132,927
Total operating revenues	400,500	463,474	757,909	737,909
Operating Segments | Natural Gas Distribution | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	327,198	381,861	615,365	605,657
Operating Segments | Natural Gas Distribution | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Natural Gas Distribution | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Natural Gas Distribution | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Natural Gas Distribution | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Natural Gas Distribution | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Clean Energy Ventures
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,169	7,865	17,075	15,181
Alternative revenue programs	0	0	0	0
Derivative instruments	6,237	3,962	10,123	6,829
Revenues out of scope	6,237	3,962	10,123	6,829
Total operating revenues	14,406	11,827	27,198	22,010
Operating Segments | Clean Energy Ventures | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Clean Energy Ventures | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Clean Energy Ventures | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Clean Energy Ventures | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Clean Energy Ventures | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,085	1,019	3,287	1,865
Operating Segments | Clean Energy Ventures | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,084	6,846	13,788	13,316
Operating Segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,836	17,309	44,684	45,188
Alternative revenue programs	0	0	0	0
Derivative instruments	179,894	395,336	473,828	736,701
Revenues out of scope	179,717	393,760	465,268	731,669
Total operating revenues	196,553	411,069	509,952	776,857
Operating Segments | Energy Services | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Energy Services | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,836	17,309	44,684	45,188
Operating Segments | Energy Services | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Energy Services | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Energy Services | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Energy Services | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Storage and Transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,303	12,805	45,017	24,389
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	19,303	12,805	45,017	24,389
Operating Segments | Storage and Transportation | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Storage and Transportation | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	20,887	13,342	47,725	25,485
Operating Segments | Storage and Transportation | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Storage and Transportation | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Storage and Transportation | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | Storage and Transportation | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0	0
Total operating revenues	13,265	13,141	27,518	26,993
Home Services and Other | Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,265	13,141	27,518	26,993
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	13,265	13,141	27,518	26,993
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	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	0
Home Services and Other | Home Services and Other | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,739	8,492	17,400	16,959
Home Services and Other | Home Services and Other | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,709	4,730	10,314	10,214
Home Services and Other | Home Services and Other | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	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	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(2,105)	(956)	(3,579)	(1,951)
Revenues out of scope	(177)	(1,576)	(8,560)	(5,032)
Eliminations | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(338)	(338)	(675)	(675)
Revenues out of scope	0	0	0	0
Eliminations | Clean Energy Ventures
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Revenues out of scope	0	0	0	0
Eliminations | Energy Services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Revenues out of scope	(177)	(1,576)	(8,560)	(5,032)
Eliminations | Storage and Transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,584)	(537)	(2,708)	(1,096)
Revenues out of scope	0	0	0	0
Eliminations | Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(183)	(81)	(196)	(180)
Revenues out of scope	$ 0	$ 0	$ 0	$ 0