REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 243,639	$ 155,392	$ 960,372	$ 720,495
Revenues out of scope	308,696	212,201	1,180,121	903,590
Total operating revenues	552,335	367,593	2,140,493	1,624,085
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	111,590	94,835	581,946	487,085
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	111,151	44,615	297,349	165,667
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,465	15,052	76,776	64,346
Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,433	890	4,301	3,397
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	537,695	354,250	2,105,663	1,592,068
Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0	0
Total operating revenues	14,168	13,071	41,161	38,002
Home Services and Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,129	12,877	41,009	37,315
Home Services and Other | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	39	194	152	687
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	180,595	118,367	785,577	604,619
Revenues out of scope	18,762	9,259	151,689	28,903
Total operating revenues	199,357	127,626	937,266	633,522
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	94,147	79,054	531,660	441,452
Natural Gas Distribution | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	65,550	23,371	172,840	95,424
Natural Gas Distribution | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,465	15,052	76,776	64,346
Natural Gas Distribution | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,433	890	4,301	3,397
Clean Energy Ventures | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,785	8,914	27,966	19,691
Revenues out of scope	1,010	4,467	7,839	6,536
Total operating revenues	13,795	13,381	35,805	26,227
Clean Energy Ventures | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,314	2,904	9,277	8,318
Clean Energy Ventures | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,471	6,010	18,689	11,373
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	10,300		42,700
Energy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	20,312	4,041	65,500	21,480
Revenues out of scope	288,924	198,475	1,020,593	868,151
Total operating revenues	309,236	202,516	1,086,093	889,631
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	20,312	4,041	65,500	21,480
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	15,779	10,999	40,168	36,703
Revenues out of scope	0	0	0	0
Total operating revenues	15,779	10,999	40,168	36,703
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	15,779	10,999	40,168	36,703
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