REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Utility	$ 463,474	$ 310,167	$ 737,909	$ 505,896
Nonutility	448,842	492,020	850,249	750,596
Operating revenues	912,316	802,187	1,588,158	1,256,492
Depreciation and amortization	31,435	26,848	61,828	54,210
Interest income	488	1,057	989	1,726
Interest expense, net of capitalized interest	18,926	20,153	38,403	39,939
Income tax provision (benefit)	28,810	39,057	59,617	56,498
Impairment of equity method investment	769	2,804	1,344	5,479
Net financial earnings (loss)	130,206	170,604	195,976	215,261
Capital expenditures	137,012	136,007	301,310	245,887
Investments in (return of capital from) equity investees	(4,000)		(4,000)
Investments in (return of capital from) equity investees		196		482
Energy Services
Segment Reporting Information [Line Items]
Operating revenues	10,300		32,400
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	901,626	793,138	1,567,968	1,237,818
Depreciation and amortization	31,258	26,537	61,545	53,821
Interest income	572	1,167	1,142	1,943
Interest expense, net of capitalized interest	18,801	18,425	38,034	37,095
Income tax provision (benefit)	27,661	36,909	59,667	54,958
Net financial earnings (loss)	130,857	172,908	195,645	217,109
Capital expenditures	136,849	135,882	301,068	245,076
Operating Segments | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	463,474	310,167	737,909	505,896
Operating Segments | Clean Energy Ventures, External Customers
Segment Reporting Information [Line Items]
Nonutility	11,827	6,476	22,010	12,846
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	411,069	459,766	776,857	687,115
Operating revenues	411,069	459,766	776,857	687,115
Depreciation and amortization	32	13	60	55
Interest expense, net of capitalized interest	795	575	1,470	1,255
Income tax provision (benefit)	(790)	23,128	19,715	35,250
Net financial earnings (loss)	29,940	96,528	47,507	98,028
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	12,805	13,257	24,389	25,704
Operating revenues	12,805	13,257	24,389	25,704
Depreciation and amortization	2,571	2,364	4,704	5,004
Interest income	381	851	758	1,545
Interest expense, net of capitalized interest	1,847	3,578	3,983	7,560
Income tax provision (benefit)	714	873	1,057	1,519
Impairment of equity method investment	1,256	3,386	2,312	6,579
Net financial earnings (loss)	4,625	4,711	7,587	8,219
Capital expenditures	43,673	20,094	109,048	27,707
Investments in (return of capital from) equity investees	(4,000)		(4,000)
Investments in (return of capital from) equity investees		196		482
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating revenues	463,474	310,167	737,909	505,896
Depreciation and amortization	23,344	19,475	46,237	38,644
Interest income	191	76	384	158
Interest expense, net of capitalized interest	10,764	9,006	21,759	17,980
Income tax provision (benefit)	29,689	15,622	42,893	23,989
Net financial earnings (loss)	102,783	80,541	153,863	130,008
Capital expenditures	52,000	97,239	125,464	176,485
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Operating revenues	11,827	6,476	22,010	12,846
Depreciation and amortization	5,311	4,685	10,544	10,118
Interest income	0	240	0	240
Interest expense, net of capitalized interest	5,395	5,266	10,822	10,300
Income tax provision (benefit)	(1,952)	(2,714)	(3,998)	(5,800)
Net financial earnings (loss)	(6,491)	(8,872)	(13,312)	(19,146)
Capital expenditures	41,176	18,549	66,556	40,884
Intercompany
Segment Reporting Information [Line Items]
Nonutility	81	252	180	419
Intercompany | Natural Gas Distribution, External Customers
Segment Reporting Information [Line Items]
Utility	338	0	675	0
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	1,576	2,803	5,032	4,931
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	537	669	1,096	1,326
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	13,141	12,521	26,993	24,931
Operating revenues	13,141	12,521	26,993	24,931
Depreciation and amortization	203	227	407	487
Interest income	147	127	302	259
Interest expense, net of capitalized interest	125	1,728	369	2,844
Income tax provision (benefit)	256	(59)	502	59
Net financial earnings (loss)	451	747	898	685
Capital expenditures	163	125	242	811
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(2,532)	(3,724)	(6,983)	(6,676)
Depreciation and amortization	(26)	84	(124)	(98)
Interest income	(231)	(237)	(455)	(476)
Income tax provision (benefit)	893	2,207	(552)	1,481
Impairment of equity method investment	(487)	(582)	(968)	(1,100)
Net financial earnings (loss)	$ (1,102)	$ (3,051)	$ (567)	$ (2,533)