REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Utility	$ 731,459	$ 729,923	$ 710,793
Nonutility	1,425,154	1,223,745	1,881,252
Operating revenues	2,156,613	1,953,668	2,592,045
Depreciation and amortization	111,387	107,368	81,109
Interest income	2,167	2,959	1,623
Interest expense, net of capitalized interest	78,559	67,597	47,082
Income tax provision (benefit)	33,286	36,494	18,440
Equity in (loss) earnings of affiliates	(83,212)	14,311	13,628
Net financial earnings (loss)	207,712	165,333	129,390
Capital expenditures	624,610	448,109	525,932
Investments in equity investees	690	2,117	4,102
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	2,106,511	1,907,687	2,551,683
Depreciation and amortization	110,683	106,628	80,480
Interest income	2,580	4,387	5,072
Interest expense, net of capitalized interest	74,505	67,628	48,370
Income tax provision (benefit)	32,430	38,687	17,385
Net financial earnings (loss)	208,327	159,451	127,572
Capital expenditures	621,980	444,879	523,448
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	731,796	729,923	710,793
Operating revenues	731,796	729,923	710,793
Depreciation and amortization	80,045	71,883	57,980
Interest income	85	538	994
Interest expense, net of capitalized interest	36,405	30,975	26,134
Income tax provision (benefit)	19,054	27,021	9,434
Net financial earnings (loss)	107,375	126,902	78,062
Capital expenditures	426,628	290,040	345,004
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	95,275	102,617	98,099
Operating revenues	95,275	102,617	98,099
Depreciation and amortization	20,567	25,329	22,376
Interest income	241	240	0
Interest expense, net of capitalized interest	22,548	20,253	14,846
Income tax provision (benefit)	5,048	11,034	7,270
Net financial earnings (loss)	16,789	22,111	31,903
Capital expenditures	87,852	133,841	157,828
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	1,228,846	1,029,303	1,734,553
Operating revenues	1,228,846	1,029,303	1,734,553
Depreciation and amortization	111	123	118
Interest income	11	99	78
Interest expense, net of capitalized interest	2,204	3,276	5,205
Income tax provision (benefit)	18,371	(3,615)	(1,573)
Net financial earnings (loss)	71,117	(7,873)	2,918
Operating Segments | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	49,252	42,015	0
Operating revenues	49,252	42,015	0
Depreciation and amortization	9,960	9,293	6
Interest income	2,243	3,510	4,000
Interest expense, net of capitalized interest	13,348	13,124	2,185
Income tax provision (benefit)	(10,043)	4,247	2,254
Equity in (loss) earnings of affiliates	(81,072)	15,903	15,832
Net financial earnings (loss)	13,046	18,311	14,689
Capital expenditures	107,500	20,998	20,616
Investments in equity investees	690	2,117	4,102
Intercompany
Segment Reporting Information [Line Items]
Nonutility	785	1,207	2,302
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	(426)	1,116	8,238
Intercompany | Storage and Transportation
Segment Reporting Information [Line Items]
Nonutility	1,768	2,713	0
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	51,444	49,810	48,600
Operating revenues	51,444	49,810	48,600
Depreciation and amortization	980	1,032	914
Interest income	522	8,633	1,942
Interest expense, net of capitalized interest	4,054	10,327	1,535
Income tax provision (benefit)	(196)	(2,478)	1,428
Net financial earnings (loss)	(826)	5,784	1,911
Capital expenditures	2,630	3,230	2,484
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(2,127)	(5,036)	(10,540)
Depreciation and amortization	(276)	(292)	(285)
Interest income	(935)	(10,061)	(5,391)
Interest expense, net of capitalized interest	0	(10,358)	(2,823)
Income tax provision (benefit)	1,052	285	(373)
Equity in (loss) earnings of affiliates	(2,140)	(1,592)	(2,204)
Net financial earnings (loss)	$ 211	$ 98	$ (93)