REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Utility		$ 199,965	$ 209,787
Nonutility		611,802	495,518
Total operating revenues		811,767	705,305
Depreciation and amortization		21,832	21,854
Interest income	[1]	199	56
Interest expense, net of capitalized interest		13,486	11,905
Income tax provision (benefit)		(6,961)	(50,168)
Equity in earnings of affiliates		3,161	3,264
Net financial earnings	[2]	54,093	135,333
Capital expenditures		94,301	67,090
Investments in equity investees		0	7,202
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues		802,129	701,764
Depreciation and amortization		21,847	21,733
Interest income	[1]	1,255	783
Interest expense, net of capitalized interest		13,961	12,310
Income tax provision (benefit)		(6,768)	(61,384)
Net financial earnings		53,939	143,144
Capital expenditures		93,570	65,777
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility		199,965	209,787
Depreciation and amortization		13,896	12,783
Interest income	[1]	199	119
Interest expense, net of capitalized interest		6,103	6,536
Income tax provision (benefit)		5,830	11,704
Net financial earnings		31,713	34,109
Capital expenditures		59,755	47,390
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility		14,897	13,996
Depreciation and amortization		7,923	8,935
Interest expense, net of capitalized interest		5,428	4,208
Income tax provision (benefit)		(23,204)	(73,988)
Net financial earnings		10,205	71,250
Capital expenditures		32,126	18,387
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	[3]	584,960	472,171
Depreciation and amortization	[4]	27	14
Interest expense, net of capitalized interest		1,887	1,257
Income tax provision (benefit)		9,644	13,743
Net financial earnings		8,370	20,274
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Depreciation and amortization		1	1
Interest income	[1]	1,056	664
Interest expense, net of capitalized interest		543	309
Income tax provision (benefit)		962	(12,843)
Equity in earnings of affiliates		3,801	4,129
Net financial earnings		3,651	17,511
Capital expenditures		1,689	0
Investments in equity investees		0	7,202
Intercompany
Segment Reporting Information [Line Items]
Nonutility		545	606
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility		2,307	5,810
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility		11,945	9,351
Depreciation and amortization		221	188
Interest income	[1]	436	204
Interest expense, net of capitalized interest		392	90
Income tax provision (benefit)		(192)	11,698
Net financial earnings		76	(7,716)
Capital expenditures		731	1,313
Eliminations
Segment Reporting Information [Line Items]
Nonutility		(2,852)	(6,416)
Depreciation and amortization		(236)	(67)
Interest income	[1]	(1,492)	(931)
Interest expense, net of capitalized interest		(867)	(495)
Income tax provision (benefit)		(1)	(482)
Equity in earnings of affiliates		(640)	(865)
Net financial earnings		$ 78	$ (95)

[1] Included in other income, net on the Unaudited Condensed Consolidated Statements of Operations.

[2] Includes income tax benefit related to the Tax Act of $57.6 million, for the three months ended December 31, 2017.

[3] Includes sales to Canada, which are immaterial

[4] The amortization of acquired wholesale energy contracts is excluded above and is included in gas purchases - nonutility on the Unaudited Condensed Consolidated Statements of Operations.