REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Utility	$ 128,532	$ 120,782	$ 645,375	$ 622,167
Nonutility	170,442	314,160	908,249	1,490,797
Total operating revenues	298,974	434,942	1,553,624	2,112,964
Depreciation and amortization	31,216	23,149	89,758	67,292
Interest income	147	496	2,054	1,114
Interest expense, net of capitalized interest	15,144	11,648	50,417	37,643
Income tax provision (benefit)	(2,190)	(1,941)	(4,092)	(11,854)
Equity in earnings of affiliates	3,213	3,495	10,191	10,027
Net financial earnings (loss)	(5,817)	(17,506)	141,524	149,004
Capital expenditures	139,890	146,616	367,239	344,018
Investments in equity investees	225	1,239	1,491	2,696
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	287,334	422,253	1,520,648	2,084,987
Depreciation and amortization	30,931	22,952	89,290	66,889
Interest income	608	1,301	3,722	3,696
Interest expense, net of capitalized interest	14,885	11,909	50,123	38,478
Income tax provision (benefit)	(2,131)	(3,642)	(6,309)	(12,355)
Net financial earnings (loss)	(5,221)	(21,911)	140,709	146,106
Capital expenditures	137,928	145,692	365,262	342,192
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	128,532	120,782	645,375	622,167
Total operating revenues	128,532	120,782	645,375	622,167
Depreciation and amortization	18,269	14,689	53,186	42,557
Interest income	135	187	378	567
Interest expense, net of capitalized interest	7,455	6,301	22,760	18,166
Income tax provision (benefit)	939	(1,391)	29,276	16,705
Net financial earnings (loss)	11,968	(3,795)	142,160	96,464
Capital expenditures	88,171	100,473	238,010	239,569
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	13,396	11,450	25,603	37,707
Total operating revenues	13,396	11,450	25,603	37,707
Depreciation and amortization	10,121	8,239	29,429	24,253
Interest expense, net of capitalized interest	5,070	4,320	14,397	14,405
Income tax provision (benefit)	4,193	(1,787)	(38,432)	(39,033)
Net financial earnings (loss)	(13,891)	(7,138)	(2,817)	24,797
Capital expenditures	41,182	38,813	110,968	91,333
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	133,740	290,083	816,003	1,416,837
Total operating revenues	133,740	290,083	816,003	1,416,837
Depreciation and amortization	28	23	84	75
Interest income	10	26	99	40
Interest expense, net of capitalized interest	517	766	2,680	4,277
Income tax provision (benefit)	(8,909)	(1,193)	(606)	7,063
Net financial earnings (loss)	(6,913)	(14,030)	(9,511)	13,644
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Nonutility	11,143	0	29,949	0
Total operating revenues	11,143	0	29,949	0
Depreciation and amortization	2,513	1	6,591	4
Interest income	463	1,088	3,245	3,089
Interest expense, net of capitalized interest	1,843	522	10,286	1,630
Income tax provision (benefit)	1,646	729	3,453	2,910
Equity in earnings of affiliates	3,615	4,167	11,200	11,966
Net financial earnings (loss)	3,615	3,052	10,877	11,201
Capital expenditures	8,575	6,406	16,284	11,290
Investments in equity investees	225	1,239	1,491	2,696
Intercompany
Segment Reporting Information [Line Items]
Nonutility	206	455	947	1,652
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	(197)	(62)	1,656	8,276
Intercompany | Midstream
Segment Reporting Information [Line Items]
Nonutility	720	0	2,062	0
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	12,163	12,627	36,694	36,253
Total operating revenues	12,163	12,627	36,694	36,253
Depreciation and amortization	265	230	761	673
Interest income	157	515	856	1,620
Interest expense, net of capitalized interest	427	407	1,264	1,410
Income tax provision (benefit)	(131)	1,705	2,044	854
Net financial earnings (loss)	(582)	4,437	675	2,932
Capital expenditures	1,962	924	1,977	1,826
Eliminations
Segment Reporting Information [Line Items]
Nonutility	(729)	(393)	(4,665)	(9,928)
Depreciation and amortization	20	(33)	(293)	(270)
Interest income	(618)	(1,320)	(2,524)	(4,202)
Interest expense, net of capitalized interest	(168)	(668)	(970)	(2,245)
Income tax provision (benefit)	72	(4)	173	(353)
Equity in earnings of affiliates	(402)	(672)	(1,009)	(1,939)
Net financial earnings (loss)	$ (14)	$ (32)	$ 140	$ (34)