REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Utility	$ 400,500	$ 463,474	$ 757,909	$ 737,909
Nonutility	243,527	448,842	609,685	850,249
Operating revenues	644,027	912,316	1,367,594	1,588,158
Depreciation and amortization	38,090	31,435	74,773	61,828
Interest income	2,236	488	4,195	989
Interest expense, net of capitalized interest	30,261	18,926	59,752	38,403
Income tax provision (benefit)	30,586	28,810	63,564	59,617
Equity in earnings of affiliates	1,131	769	2,077	1,344
Net financial earnings (loss)	112,310	130,206	222,594	195,976
Capital expenditures	117,188	137,012	263,111	301,310
Return of capital from equity investees	0	(4,000)	0	(4,000)
Energy Services
Segment Reporting Information [Line Items]
Operating revenues	9,500	10,300	29,500	32,400
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	632,861	901,626	1,352,019	1,567,968
Depreciation and amortization	37,866	31,258	74,331	61,545
Interest income	2,440	572	4,523	1,142
Interest expense, net of capitalized interest	30,072	18,801	59,441	38,034
Income tax provision (benefit)	27,431	27,661	61,984	59,667
Net financial earnings (loss)	114,893	130,857	224,751	195,645
Capital expenditures	116,428	136,849	262,211	301,068
Operating Segments | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	400,500	463,474	757,909	737,909
Operating Segments | Clean Energy Ventures, External Customers
Segment Reporting Information [Line Items]
Nonutility	14,406	11,827	27,198	22,010
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	196,553	411,069	509,952	776,857
Operating revenues	196,553	411,069	509,952	776,857
Depreciation and amortization	62	32	119	60
Interest income	380	0	649	0
Interest expense, net of capitalized interest	2,749	795	5,807	1,470
Income tax provision (benefit)	5,916	(790)	25,980	19,715
Net financial earnings (loss)	21,125	29,940	73,658	47,507
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	19,303	12,805	45,017	24,389
Operating revenues	19,303	12,805	45,017	24,389
Depreciation and amortization	6,020	2,571	11,962	4,704
Interest income	1,684	381	3,085	758
Interest expense, net of capitalized interest	6,128	1,847	12,835	3,983
Income tax provision (benefit)	596	714	2,539	1,057
Equity in earnings of affiliates	977	1,256	1,886	2,312
Net financial earnings (loss)	2,450	4,625	8,693	7,587
Capital expenditures	10,122	43,673	29,841	109,048
Return of capital from equity investees	0	(4,000)	0	(4,000)
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating revenues	400,500	463,474	757,909	737,909
Depreciation and amortization	25,319	23,344	50,209	46,237
Interest income	376	191	789	384
Interest expense, net of capitalized interest	13,879	10,764	27,588	21,759
Income tax provision (benefit)	23,924	29,689	38,307	42,893
Net financial earnings (loss)	100,697	102,783	155,361	153,863
Capital expenditures	92,600	52,000	174,671	125,464
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Operating revenues	14,406	11,827	27,198	22,010
Depreciation and amortization	6,465	5,311	12,041	10,544
Interest expense, net of capitalized interest	7,316	5,395	13,211	10,822
Income tax provision (benefit)	(3,005)	(1,952)	(4,842)	(3,998)
Net financial earnings (loss)	(9,379)	(6,491)	(12,961)	(13,312)
Capital expenditures	13,706	41,176	57,699	66,556
Intercompany
Segment Reporting Information [Line Items]
Nonutility	183	81	196	180
Intercompany | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	338	338	675	675
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	177	1,576	8,560	5,032
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	1,584	537	2,708	1,096
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	13,265	13,141	27,518	26,993
Operating revenues	13,265	13,141	27,518	26,993
Depreciation and amortization	224	203	442	407
Interest income	734	147	1,388	302
Interest expense, net of capitalized interest	189	125	311	369
Income tax provision (benefit)	488	256	705	502
Net financial earnings (loss)	813	451	784	898
Capital expenditures	760	163	900	242
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(2,282)	(2,532)	(12,139)	(6,983)
Depreciation and amortization	0	(26)	0	(124)
Interest income	(938)	(231)	(1,716)	(455)
Income tax provision (benefit)	2,667	893	875	(552)
Equity in earnings of affiliates	154	(487)	191	(968)
Net financial earnings (loss)	$ (3,396)	$ (1,102)	$ (2,941)	$ (567)