REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Jun. 30, 2019		Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Utility		$ 120,782		$ 104,538		$ 622,167	$ 631,389
Nonutility		314,160		438,897		1,490,797	1,636,394
Total operating revenues		434,942		543,435		2,112,964	2,267,783
Depreciation and amortization		23,149		20,320		67,292	64,634
Interest income	[1]	496		202		1,114	452
Interest expense, net of capitalized interest		11,648		11,037		37,643	34,740
Income tax provision (benefit)		(1,941)		(28,534)		(11,854)	(47,801)
Equity in earnings of affiliates		3,495		3,213		10,027	9,670
Net financial (loss) earnings	[2]	(17,506)		(8,003)		149,004	269,392
Capital expenditures		146,616		101,767		344,018	266,705
Investments in equity investees		1,239		3,319		2,696	14,496
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues		422,253		529,291		2,084,987	2,286,298
Depreciation and amortization		22,952		20,197		66,889	64,228
Interest income	[1]	1,301		1,281		3,696	3,072
Interest expense, net of capitalized interest		11,909		11,986		38,478	36,751
Income tax provision (benefit)		(3,642)		(29,676)		(12,355)	(58,695)
Net financial (loss) earnings		(21,911)		(9,979)		146,106	277,805
Capital expenditures		145,692		101,022		342,192	265,405
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility		120,782		104,538		622,167	631,389
Depreciation and amortization		14,689		13,473		42,557	39,609
Interest income		187	[1]	202	[1]	567	452	[1]
Interest expense, net of capitalized interest		6,301		6,226		18,166	19,285
Income tax provision (benefit)		(1,391)		(25,314)		16,705	4,381
Net financial (loss) earnings		(3,795)		2,440		96,464	96,991
Capital expenditures		100,473		70,623		239,569	173,410
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility		11,450		15,348		37,707	42,210
Depreciation and amortization		8,239		6,702		24,253	24,565
Interest expense, net of capitalized interest		4,320		4,708		14,405	13,260
Income tax provision (benefit)		(1,787)		(565)		(39,033)	(87,275)
Net financial (loss) earnings		(7,138)		(829)		24,797	80,472
Capital expenditures		38,813		29,424		91,333	88,416
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	[3]	290,083		409,417		1,416,837	1,563,063
Depreciation and amortization	[4]	23		21		75	50
Interest income		26	[1]	134	[1]	40	240	[1]
Interest expense, net of capitalized interest		766		581		4,277	3,041
Income tax provision (benefit)		(1,193)		(4,786)		7,063	32,922
Net financial (loss) earnings		(14,030)		(15,079)		13,644	78,027
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Depreciation and amortization		1		1		4	4
Interest income		1,088	[1]	945	[1]	3,089	2,380	[1]
Interest expense, net of capitalized interest		522		471		1,630	1,165
Income tax provision (benefit)		729		989		2,910	(8,723)
Equity in earnings of affiliates		4,167		3,907		11,966	12,104
Net financial (loss) earnings		3,052		3,489		11,201	22,315
Capital expenditures		6,406		975		11,290	3,579
Investments in equity investees		1,239		3,319		2,696	14,496
Intercompany
Segment Reporting Information [Line Items]
Nonutility		455		627		1,652	1,856
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility		(62)		(12)		8,276	49,636
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility		12,627		14,132		36,253	31,121
Depreciation and amortization		230		193		673	570
Interest income		515	[1]	340	[1]	1,620	898	[1]
Interest expense, net of capitalized interest		407		(129)		1,410	(18)
Income tax provision (benefit)		1,705		1,122		854	11,539
Net financial (loss) earnings		4,437		1,993		2,932	(8,211)
Capital expenditures		924		745		1,826	1,300
Eliminations
Segment Reporting Information [Line Items]
Nonutility		(393)		(615)		(9,928)	(51,492)
Depreciation and amortization		(33)		(70)		(270)	(164)
Interest income		(1,320)	[1]	(1,419)	[1]	(4,202)	(3,518)	[1]
Interest expense, net of capitalized interest		(668)		(820)		(2,245)	(1,993)
Income tax provision (benefit)		(4)		20		(353)	(645)
Equity in earnings of affiliates		(672)		(694)		(1,939)	(2,434)
Net financial (loss) earnings		$ (32)		$ (17)		$ (34)	$ (202)

[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 $844,000 and $57.7 million, for the three and nine months ended June 30, 2018, respectively.

[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.