REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Utility	$ 199,357	$ 127,626	$ 937,266	$ 633,522
Nonutility	352,978	239,967	1,203,227	990,563
Operating revenues	552,335	367,593	2,140,493	1,624,085
Depreciation and amortization	32,872	27,767	94,700	81,977
Interest income	684	347	1,673	2,073
Interest expense, net of capitalized interest	21,411	18,744	59,814	58,683
Income tax provision (benefit)	4,434	(18,785)	64,051	37,713
Equity in earnings (loss) of affiliates	4,801	(89,233)	6,145	(83,754)
Net financial earnings (loss)	(3,551)	(14,148)	192,425	201,113
Capital expenditures	139,804	184,026	441,114	429,913
Investments in (return of capital from) equity investees	(1,479)		(5,479)
Investments in (return of capital from) equity investees		208		690
Energy Services
Segment Reporting Information [Line Items]
Operating revenues	10,300		42,700
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	537,695	354,250	2,105,663	1,592,068
Depreciation and amortization	32,666	27,565	94,211	81,386
Interest income	751	451	1,893	2,394
Interest expense, net of capitalized interest	21,276	16,842	59,310	53,937
Income tax provision (benefit)	3,995	(19,757)	63,662	35,201
Net financial earnings (loss)	(3,927)	(13,485)	191,718	203,624
Capital expenditures	139,484	183,782	440,552	428,858
Operating Segments | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	199,357	127,626	937,266	633,522
Operating Segments | Clean Energy Ventures, External Customers
Segment Reporting Information [Line Items]
Nonutility	13,795	13,381	35,805	26,227
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	309,236	202,516	1,086,093	889,631
Operating revenues	309,236	202,516	1,086,093	889,631
Depreciation and amortization	34	28	94	83
Interest income	0	11	0	11
Interest expense, net of capitalized interest	1,115	240	2,585	1,495
Income tax provision (benefit)	2,338	(8,805)	22,053	26,445
Net financial earnings (loss)	(5,003)	(12,527)	42,504	85,501
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	15,779	10,999	40,168	36,703
Operating revenues	15,779	10,999	40,168	36,703
Depreciation and amortization	3,323	2,443	8,027	7,447
Interest income	501	350	1,259	1,895
Interest expense, net of capitalized interest	3,177	2,937	7,160	10,497
Income tax provision (benefit)	1,675	(10,393)	2,732	(8,874)
Equity in earnings (loss) of affiliates	5,274	(88,615)	7,586	(82,036)
Net financial earnings (loss)	3,526	2,387	11,113	10,606
Capital expenditures	20,560	22,479	129,608	50,186
Investments in (return of capital from) equity investees	(1,479)		(5,479)
Investments in (return of capital from) equity investees		208		690
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating revenues	199,357	127,626	937,266	633,522
Depreciation and amortization	23,951	19,894	70,188	58,538
Interest income	250	90	634	248
Interest expense, net of capitalized interest	11,474	8,667	33,233	26,647
Income tax provision (benefit)	1,508	889	44,401	24,878
Net financial earnings (loss)	2,648	1,581	156,511	131,589
Capital expenditures	79,976	150,642	205,440	327,127
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Operating revenues	13,795	13,381	35,805	26,227
Depreciation and amortization	5,358	5,200	15,902	15,318
Interest income	0	0	0	240
Interest expense, net of capitalized interest	5,510	4,998	16,332	15,298
Income tax provision (benefit)	(1,526)	(1,448)	(5,524)	(7,248)
Net financial earnings (loss)	(5,098)	(4,926)	(18,410)	(24,072)
Capital expenditures	38,948	10,661	105,504	51,545
Intercompany
Segment Reporting Information [Line Items]
Nonutility	52	241	232	660
Intercompany | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	338	0	1,013	0
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	(1,421)	(922)	3,611	4,009
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	611	650	1,707	1,976
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	14,168	13,071	41,161	38,002
Operating revenues	14,168	13,071	41,161	38,002
Depreciation and amortization	207	260	614	747
Interest income	225	129	527	388
Interest expense, net of capitalized interest	135	1,902	504	4,746
Income tax provision (benefit)	180	415	682	474
Net financial earnings (loss)	215	(384)	1,113	301
Capital expenditures	320	244	562	1,055
Eliminations
Segment Reporting Information [Line Items]
Nonutility	420	31	(6,563)	(6,645)
Depreciation and amortization	(1)	(58)	(125)	(156)
Interest income	(292)	(233)	(747)	(709)
Income tax provision (benefit)	259	557	(293)	2,038
Equity in earnings (loss) of affiliates	(473)	(618)	(1,441)	(1,718)
Net financial earnings (loss)	$ 161	$ (279)	$ (406)	$ (2,812)