REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Utility	$ 297,220	$ 301,420	$ 516,843	$ 501,385
Nonutility	342,394	564,835	737,807	1,176,637
Total operating revenues	639,614	866,255	1,254,650	1,678,022
Depreciation and amortization	30,784	22,311	58,542	44,143
Interest income	1,721	419	1,907	618
Interest expense, net of capitalized interest	19,203	12,509	35,273	25,995
Income tax provision (benefit)	(1,643)	(2,952)	(1,902)	(9,913)
Equity in earnings of affiliates	3,589	3,371	6,978	6,532
Net financial (loss) earnings	106,936	112,417	147,341	166,510
Capital expenditures	101,166	103,101	227,349	197,402
Investments in equity investees	757	1,457	1,266	1,457
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	627,992	860,605	1,233,314	1,662,734
Depreciation and amortization	30,395	22,090	58,359	43,937
Interest income	2,273	1,140	3,114	2,395
Interest expense, net of capitalized interest	18,866	12,608	35,238	26,569
Income tax provision (benefit)	(3,703)	(1,945)	(4,178)	(8,713)
Net financial (loss) earnings	106,897	114,078	145,930	168,017
Capital expenditures	101,277	98,046	227,334	191,616
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	297,220	301,420	516,843	501,385
Total operating revenues	297,220	301,420	516,843	501,385
Depreciation and amortization	18,100	13,972	34,917	27,868
Interest income	136	181	243	380
Interest expense, net of capitalized interest	7,473	5,762	15,305	11,865
Income tax provision (benefit)	19,702	12,266	28,337	18,096
Net financial (loss) earnings	86,336	68,546	130,192	100,259
Capital expenditures	72,042	79,341	149,839	139,096
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	5,995	11,360	12,207	26,257
Total operating revenues	5,995	11,360	12,207	26,257
Depreciation and amortization	9,871	8,091	19,308	16,014
Interest expense, net of capitalized interest	4,835	4,657	9,327	10,085
Income tax provision (benefit)	(22,061)	(14,042)	(42,625)	(37,246)
Net financial (loss) earnings	15,990	21,730	11,074	31,935
Capital expenditures	24,087	20,394	69,786	52,520
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	313,959	541,794	682,263	1,126,754
Total operating revenues	313,959	541,794	682,263	1,126,754
Depreciation and amortization	27	25	56	52
Interest income	52	14	89	14
Interest expense, net of capitalized interest	937	1,624	2,163	3,511
Income tax provision (benefit)	(2,449)	(1,388)	8,303	8,256
Net financial (loss) earnings	313	19,304	(2,598)	27,674
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Nonutility	10,401	0	18,806	0
Total operating revenues	10,401	0	18,806	0
Depreciation and amortization	2,397	2	4,078	3
Interest income	2,085	945	2,782	2,001
Interest expense, net of capitalized interest	5,621	565	8,443	1,108
Income tax provision (benefit)	1,105	1,219	1,807	2,181
Equity in earnings of affiliates	3,921	3,998	7,585	7,799
Net financial (loss) earnings	4,258	4,498	7,262	8,149
Capital expenditures	5,148	(1,689)	7,709	0
Investments in equity investees	757	1,457	1,266	1,457
Intercompany
Segment Reporting Information [Line Items]
Nonutility	326	652	741	1,197
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	(258)	6,031	1,853	8,338
Intercompany | Midstream
Segment Reporting Information [Line Items]
Nonutility	675	0	1,342	0
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	12,039	11,681	24,531	23,626
Total operating revenues	12,039	11,681	24,531	23,626
Depreciation and amortization	250	222	496	443
Interest income	208	669	699	1,105
Interest expense, net of capitalized interest	565	611	837	1,003
Income tax provision (benefit)	1,956	(659)	2,175	(851)
Net financial (loss) earnings	148	(1,581)	1,257	(1,505)
Capital expenditures	(111)	5,055	15	5,786
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(743)	(6,683)	(3,936)	(9,535)
Depreciation and amortization	139	(1)	(313)	(237)
Interest income	(760)	(1,390)	(1,906)	(2,882)
Interest expense, net of capitalized interest	(228)	(710)	(802)	(1,577)
Income tax provision (benefit)	104	(348)	101	(349)
Equity in earnings of affiliates	(332)	(627)	(607)	(1,267)
Net financial (loss) earnings	$ (109)	$ (80)	$ 154	$ (2)