REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 284,090	$ 225,727
Revenues out of scope	391,752	228,578
Total operating revenues	675,842	454,305
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	168,055	152,150
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	91,068	50,666
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,675	21,104
Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,292	1,807
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	666,342	444,680
Home Services and Other
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0
Total operating revenues	13,852	12,410
Home Services and Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,775	12,204
Home Services and Other | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	77	206
Home Services and Other | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Home Services and Other | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	223,459	189,364
Revenues out of scope	50,976	6,365
Total operating revenues	274,435	195,729
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	151,308	137,224
Natural Gas Distribution | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47,184	29,229
Natural Gas Distribution | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,675	21,104
Natural Gas Distribution | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,292	1,807
Clean Energy Ventures | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,316	5,078
Revenues out of scope	2,867	1,292
Total operating revenues	10,183	6,370
Clean Energy Ventures | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,972	2,722
Clean Energy Ventures | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,344	2,356
Clean Energy Ventures | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Clean Energy Ventures | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Energy Services
Disaggregation of Revenue [Line Items]
Total operating revenues	22,100
Energy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	27,879	6,428
Revenues out of scope	337,909	220,921
Total operating revenues	365,788	227,349
Energy Services | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Energy Services | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	27,879	6,428
Energy Services | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Energy Services | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Storage and Transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,584	12,447
Revenues out of scope	0	0
Total operating revenues	11,584	12,447
Storage and Transportation | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Storage and Transportation | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,584	12,447
Storage and Transportation | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Storage and Transportation | Operating Segments | Interruptible and off-tariff
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0