REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Utility	$ 144,971	$ 199,357	$ 902,880	$ 937,266
Nonutility	119,104	352,978	728,789	1,203,227
Operating revenues	264,075	552,335	1,631,669	2,140,493
Depreciation and amortization	38,877	32,872	113,650	94,700
Interest income	2,390	684	6,585	1,673
Interest expense, net of capitalized interest	30,119	21,411	89,871	59,814
Income tax provision (benefit)	(20,505)	4,434	43,059	64,051
Equity in earnings of affiliates	701	4,801	2,778	6,145
Net financial earnings (loss)	9,670	(3,551)	232,264	192,425
Capital expenditures	117,103	139,804	380,214	441,114
Return of capital from equity investees	0	(1,479)	0	(5,479)
Energy Services
Segment Reporting Information [Line Items]
Operating revenues	9,500	10,300	39,000	42,700
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	250,859	537,695	1,602,878	2,105,663
Depreciation and amortization	38,650	32,666	112,981	94,211
Interest income	2,647	751	7,170	1,893
Interest expense, net of capitalized interest	29,971	21,276	89,412	59,310
Income tax provision (benefit)	(20,440)	3,995	41,544	63,662
Net financial earnings (loss)	8,912	(3,927)	233,663	191,718
Capital expenditures	116,910	139,484	379,121	440,552
Operating Segments | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	144,971	199,357	902,880	937,266
Operating Segments | Clean Energy Ventures, External Customers
Segment Reporting Information [Line Items]
Nonutility	13,178	13,795	40,376	35,805
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	69,542	309,236	579,494	1,086,093
Operating revenues	69,542	309,236	579,494	1,086,093
Depreciation and amortization	51	34	170	94
Interest income	310	0	959	0
Interest expense, net of capitalized interest	2,467	1,115	8,274	2,585
Income tax provision (benefit)	(2,934)	2,338	23,046	22,053
Net financial earnings (loss)	(1,604)	(5,003)	72,054	42,504
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	21,435	15,779	66,452	40,168
Operating revenues	21,435	15,779	66,452	40,168
Depreciation and amortization	6,102	3,323	18,064	8,027
Interest income	1,841	501	4,926	1,259
Interest expense, net of capitalized interest	6,430	3,177	19,265	7,160
Income tax provision (benefit)	535	1,675	3,074	2,732
Equity in earnings of affiliates	377	5,274	2,263	7,586
Net financial earnings (loss)	2,358	3,526	11,051	11,113
Capital expenditures	3,450	20,560	33,291	129,608
Return of capital from equity investees	0	(1,479)	0	(5,479)
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating revenues	144,971	199,357	902,880	937,266
Depreciation and amortization	25,825	23,951	76,034	70,188
Interest income	496	250	1,285	634
Interest expense, net of capitalized interest	13,226	11,474	40,814	33,233
Income tax provision (benefit)	196	1,508	38,503	44,401
Net financial earnings (loss)	891	2,648	156,252	156,511
Capital expenditures	102,555	79,976	277,226	205,440
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Operating revenues	13,178	13,795	40,376	35,805
Depreciation and amortization	6,672	5,358	18,713	15,902
Interest expense, net of capitalized interest	7,848	5,510	21,059	16,332
Income tax provision (benefit)	(18,237)	(1,526)	(23,079)	(5,524)
Net financial earnings (loss)	7,267	(5,098)	(5,694)	(18,410)
Capital expenditures	10,905	38,948	68,604	105,504
Intercompany
Segment Reporting Information [Line Items]
Nonutility	6	52	202	232
Intercompany | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	337	338	1,012	1,013
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	630	(1,421)	9,190	3,611
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	766	611	3,474	1,707
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	14,949	14,168	42,467	41,161
Operating revenues	14,949	14,168	42,467	41,161
Depreciation and amortization	227	207	669	614
Interest income	753	225	2,141	527
Interest expense, net of capitalized interest	148	135	459	504
Income tax provision (benefit)	429	180	1,134	682
Net financial earnings (loss)	523	215	1,307	1,113
Capital expenditures	193	320	1,093	562
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(1,739)	420	(13,878)	(6,563)
Depreciation and amortization	0	(1)	0	(125)
Interest income	(1,010)	(292)	(2,726)	(747)
Income tax provision (benefit)	(494)	259	381	(293)
Equity in earnings of affiliates	324	(473)	515	(1,441)
Net financial earnings (loss)	$ 235	$ 161	$ (2,706)	$ (406)