BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Utility	$ 185,556	$ 151,606
Nonutility	355,472	292,652
Total operating revenues	541,028	444,258
Depreciation and amortization	19,260	16,482
Interest income	75	70
Interest expense, net of capitalized interest	10,615	6,777
Income tax provision (benefit)	2,018	6,722
Equity in earnings of affiliates	2,311	2,406
Net financial earnings	40,383	51,267
Capital expenditures	85,811	94,843
Investments in equity investees	$ 4,636	$ 2,846
Canada
Segment Reporting Information [Line Items]
Percentage to total operating revenues	1.90%	3.50%
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	$ 530,304	$ 438,093
Depreciation and amortization	19,088	16,372
Interest income	537	404
Interest expense, net of capitalized interest	10,775	6,891
Income tax provision (benefit)	1,473	8,318
Net financial earnings	39,064	51,226
Capital expenditures	85,640	94,046
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Utility	185,556	151,606
Depreciation and amortization	12,030	11,238
Interest income	75	68
Interest expense, net of capitalized interest	6,824	4,588
Income tax provision (benefit)	14,887	13,507
Net financial earnings	30,348	30,926
Capital expenditures	38,855	49,040
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Nonutility	7,567	7,794
Depreciation and amortization	7,041	5,110
Interest expense, net of capitalized interest	3,324	2,053
Income tax provision (benefit)	(11,887)	(11,734)
Net financial earnings	2,842	7,652
Capital expenditures	46,785	45,006
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Nonutility	338,930	276,182
Depreciation and amortization	16	23
Interest income	0	72
Interest expense, net of capitalized interest	571	208
Income tax provision (benefit)	(3,176)	4,905
Net financial earnings	3,487	10,304
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Depreciation and amortization	1	1
Interest income	462	264
Interest expense, net of capitalized interest	56	42
Income tax provision (benefit)	1,649	1,640
Equity in earnings of affiliates	3,331	3,545
Net financial earnings	2,387	2,344
Investments in equity investees	4,636	2,846
Intercompany
Segment Reporting Information [Line Items]
Nonutility	1,031	897
Intercompany | Energy Services
Segment Reporting Information [Line Items]
Nonutility	(1,749)	2,511
Home Services and Other
Segment Reporting Information [Line Items]
Nonutility	8,975	8,676
Depreciation and amortization	221	227
Interest income	121	37
Interest expense, net of capitalized interest	74	0
Income tax provision (benefit)	(245)	(1,130)
Net financial earnings	1,542	259
Capital expenditures	171	797
Eliminations
Segment Reporting Information [Line Items]
Nonutility	718	(3,408)
Depreciation and amortization	(49)	(117)
Interest income	(583)	(371)
Interest expense, net of capitalized interest	(234)	(114)
Income tax provision (benefit)	790	(466)
Equity in earnings of affiliates	(1,020)	(1,139)
Net financial earnings	$ (223)	$ (218)