REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 199,315	$ 243,639	$ 948,299	$ 960,372
Revenues out of scope	64,760	308,696	683,370	1,180,121
Total operating revenues	264,075	552,335	1,631,669	2,140,493
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	112,847	111,590	611,174	581,946
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	67,112	111,151	260,540	297,349
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,088	19,465	73,655	76,776
Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,268	1,433	2,930	4,301
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	250,859	537,695	1,602,878	2,105,663
Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0	0
Total operating revenues	14,949	14,168	42,467	41,161
Home Services and Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,922	14,129	42,191	41,009
Home Services and Other | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	27	39	276	152
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	133,916	180,595	748,606	785,577
Revenues out of scope	11,055	18,762	154,274	151,689
Total operating revenues	144,971	199,357	902,880	937,266
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	94,340	94,147	558,901	531,660
Natural Gas Distribution | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	20,220	65,550	113,120	172,840
Natural Gas Distribution | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,088	19,465	73,655	76,776
Natural Gas Distribution | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,268	1,433	2,930	4,301
Clean Energy Ventures | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,994	12,785	30,069	27,966
Revenues out of scope	184	1,010	10,307	7,839
Total operating revenues	13,178	13,795	40,376	35,805
Clean Energy Ventures | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,585	3,314	10,082	9,277
Clean Energy Ventures | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,409	9,471	19,987	18,689
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	39,000	42,700
Energy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,021	20,312	60,705	65,500
Revenues out of scope	53,521	288,924	518,789	1,020,593
Total operating revenues	69,542	309,236	579,494	1,086,093
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	16,021	20,312	60,705	65,500
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	21,435	15,779	66,452	40,168
Revenues out of scope	0	0	0	0
Total operating revenues	21,435	15,779	66,452	40,168
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	21,435	15,779	66,452	40,168
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