REVENUE - DISAGGREGATED REVENUE - TYPE (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
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
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	263,916	302,301	498,327	470,356
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	90,385	95,130	193,428	186,198
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	29,368	34,636	55,567	57,311
Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	764	576	1,662	2,868
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	632,861	901,626	1,352,019	1,567,968
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 | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,089	13,105	27,269	26,880
Home Services and Other | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	176	36	249	113
Home Services and Other | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Home Services and Other | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	326,860	381,523	614,690	604,982
Revenues out of scope	73,640	81,951	143,219	132,927
Total operating revenues	400,500	463,474	757,909	737,909
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	247,623	286,205	464,561	437,513
Natural Gas Distribution | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	49,105	60,106	92,900	107,290
Natural Gas Distribution | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	29,368	34,636	55,567	57,311
Natural Gas Distribution | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	764	576	1,662	2,868
Clean Energy Ventures | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,169	7,865	17,075	15,181
Revenues out of scope	6,237	3,962	10,123	6,829
Total operating revenues	14,406	11,827	27,198	22,010
Clean Energy Ventures | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,204	2,991	6,497	5,963
Clean Energy Ventures | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,965	4,874	10,578	9,218
Clean Energy Ventures | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	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	0
Energy Services
Disaggregation of Revenue [Line Items]
Total operating revenues	9,500	10,300	29,500	32,400
Energy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,836	17,309	44,684	45,188
Revenues out of scope	179,717	393,760	465,268	731,669
Total operating revenues	196,553	411,069	509,952	776,857
Energy Services | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Energy Services | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,836	17,309	44,684	45,188
Energy Services | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Energy Services | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Storage and Transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,303	12,805	45,017	24,389
Revenues out of scope	0	0	0	0
Total operating revenues	19,303	12,805	45,017	24,389
Storage and Transportation | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Storage and Transportation | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,303	12,805	45,017	24,389
Storage and Transportation | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	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	$ 0