REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Utility	$ 219,623	$ 199,965
Nonutility	395,413	611,802
Total operating revenues	615,036	811,767
Depreciation and amortization	27,758	21,832
Interest income	186	199
Interest expense, net of capitalized interest	16,070	13,486
Income tax provision (benefit)	(259)	(6,961)
Equity in earnings of affiliates	3,389	3,161
Net financial (loss) earnings	40,405	54,093
Capital expenditures	126,183	94,301
Investments in equity investees	509	0
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	605,322	802,129
Depreciation and amortization	27,964	21,847
Interest income	841	1,255
Interest expense, net of capitalized interest	16,372	13,961
Income tax provision (benefit)	(475)	(6,768)
Net financial (loss) earnings	39,033	53,939
Capital expenditures	126,057	93,570
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	219,623	199,965
Total operating revenues	219,623	199,965
Depreciation and amortization	16,817	13,896
Interest income	107	199
Interest expense, net of capitalized interest	7,832	6,103
Income tax provision (benefit)	8,635	5,830
Net financial (loss) earnings	43,856	31,713
Capital expenditures	77,797	59,755
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	6,212	14,897
Total operating revenues	6,212	14,897
Depreciation and amortization	9,437	7,923
Interest expense, net of capitalized interest	4,492	5,428
Income tax provision (benefit)	(20,564)	(23,204)
Net financial (loss) earnings	(4,916)	10,205
Capital expenditures	45,699	32,126
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	368,304	584,960
Total operating revenues	368,304	584,960
Depreciation and amortization	29	27
Interest income	37	0
Interest expense, net of capitalized interest	1,226	1,887
Income tax provision (benefit)	10,752	9,644
Net financial (loss) earnings	(2,911)	8,370
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Nonutility	8,405	0
Total operating revenues	8,405	0
Depreciation and amortization	1,681	1
Interest income	697	1,056
Interest expense, net of capitalized interest	2,822	543
Income tax provision (benefit)	702	962
Equity in earnings of affiliates	3,664	3,801
Net financial (loss) earnings	3,004	3,651
Capital expenditures	2,561	1,689
Investments in equity investees	509	0
Intercompany
Segment Reporting Information [Line Items]
Nonutility	415	545
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	2,111	2,307
Intercompany | Midstream
Segment Reporting Information [Line Items]
Nonutility	667	0
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	12,492	11,945
Total operating revenues	12,492	11,945
Depreciation and amortization	246	221
Interest income	491	436
Interest expense, net of capitalized interest	272	392
Income tax provision (benefit)	219	(192)
Net financial (loss) earnings	1,109	76
Capital expenditures	126	731
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(3,193)	(2,852)
Depreciation and amortization	(452)	(236)
Interest income	(1,146)	(1,492)
Interest expense, net of capitalized interest	(574)	(867)
Income tax provision (benefit)	(3)	(1)
Equity in earnings of affiliates	(275)	(640)
Net financial (loss) earnings	$ 263	$ 78