BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Utility		$ 151,606	$ 208,727
Nonutility		292,652	615,397
Total operating revenues		444,258	824,124
Depreciation and amortization		16,482	14,386
Interest income	[1]	70	90
Interest expense, net of capitalized interest		6,777	7,195
Income tax provision (benefit)		8,357	40,867
Equity in earnings of affiliates		2,406	2,795
Net financial earnings		49,632	55,109
Capital expenditures		94,843	92,104
Investments in equity investees		$ 2,846	$ 547
Canada [Member]
Segment Reporting Information [Line Items]
Percentage to total operating revenues		3.50%	4.70%
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total operating revenues		$ 438,093	$ 818,650
Depreciation and amortization		16,372	14,160
Interest income	[1]	404	329
Interest expense, net of capitalized interest		6,891	7,189
Income tax provision (benefit)		9,111	41,814
Net financial earnings		50,433	55,750
Capital expenditures		94,046	92,093
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		11,238	10,545
Interest income	[1]	68	90
Interest expense, net of capitalized interest		4,588	4,609
Income tax provision (benefit)		13,863	14,166
Net financial earnings		30,570	28,186
Capital expenditures		49,040	36,748
Operating Segments [Member] | Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility		151,606	208,727
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		23	22
Interest income	[1]	72	0
Interest expense, net of capitalized interest		208	513
Income tax provision (benefit)		5,195	45,877
Net financial earnings		10,014	16,436
Operating Segments [Member] | Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	[2]	276,182	600,562
Operating Segments [Member] | Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility		2,511	3,126
Operating Segments [Member] | Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		5,110	3,591
Interest expense, net of capitalized interest		2,053	1,817
Income tax provision (benefit)		(11,587)	(19,721)
Net financial earnings		7,505	9,008
Capital expenditures		45,006	55,345
Operating Segments [Member] | Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility		7,794	6,235
Operating Segments [Member] | Home Services and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		227	238
Interest income	[1]	37	0
Interest expense, net of capitalized interest		0	6
Income tax provision (benefit)		(288)	(452)
Net financial earnings		(583)	(592)
Capital expenditures		797	11
Operating Segments [Member] | Home Services and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility		8,676	8,600
Operating Segments [Member] | Home Services and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility		897	411
Operating Segments [Member] | Midstream [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		1	2
Interest income	[1]	264	239
Interest expense, net of capitalized interest		42	250
Income tax provision (benefit)		1,640	1,492
Equity in earnings of affiliates		3,545	3,775
Net financial earnings		2,344	2,120
Investments in equity investees		2,846	547
Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility		(3,408)	(3,537)
Depreciation and amortization		(117)	(12)
Interest income	[1]	(371)	(239)
Interest expense, net of capitalized interest		(114)	0
Income tax provision (benefit)		(466)	(495)
Equity in earnings of affiliates		(1,139)	(980)
Net financial earnings		$ (218)	$ (49)

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

[2] Includes sales to Canada, which accounted for 3.5 and 4.7 percent of total operating revenues during the three months ended December 31, 2015 and 2014.