BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Segment Reporting Information [Line Items]
Utility	$ 111,383		$ 119,022		$ 739,380		$ 689,621
Nonutility	576,874		648,447		2,406,851		1,774,752
Total operating revenues	688,257		767,469		3,146,231		2,464,373
Depreciation and amortization	13,620		11,942		39,014		34,966
Interest income	278	[1]	193	[1]	790	[1]	592	[1]
Interest expense, net of capitalized interest	6,507		6,008		19,108		17,579
Income tax provision (benefit)	(7,808)		15,297		65,377		51,342
Equity in earnings of affiliates	2,681		2,222		8,056		8,307
Net financial earnings (loss)	4,514		9,738		196,295		113,895
Capital expenditures	84,511		44,266		201,276		135,128
Canada
Segment Reporting Information [Line Items]
Percentage to total operating revenues					3.60%		6.40%
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total operating revenues	675,171		755,118		3,187,313		2,437,884
Depreciation and amortization	13,406		11,745		38,387		34,381
Interest income	518	[1]	411	[1]	1,498	[1]	1,258	[1]
Interest expense, net of capitalized interest	6,421		5,747		18,780		16,760
Income tax provision (benefit)	(9,301)		14,329		64,816		51,227
Net financial earnings (loss)	2,015		7,785		195,587		113,094
Capital expenditures	84,352		44,032		200,640		134,596
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	10,567		9,537		30,374		28,213
Interest income	137	[1]	146	[1]	579	[1]	459	[1]
Interest expense, net of capitalized interest	4,540		3,796		12,412		10,929
Income tax provision (benefit)	4,348		1,788		42,256		39,089
Net financial earnings (loss)	4,882		5,528		79,564		76,937
Capital expenditures	38,186		29,141		109,071		94,840
Operating Segments [Member] | Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility	111,383		119,022		739,380		689,621
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	15		10		40		32
Interest income	210	[1]	0	[1]	210	[1]	0	[1]
Interest expense, net of capitalized interest	166		615		1,443		1,823
Income tax provision (benefit)	(16,256)		12,945		36,816		23,906
Net financial earnings (loss)	(8,628)		2,097		90,153		21,479
Operating Segments [Member] | Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	560,115	[2]	632,414	[2]	2,367,641	[2]	1,735,411	[2]
Operating Segments [Member] | Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	518		1,119		72,285		5,670
Operating Segments [Member] | Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2,823		2,196		7,969		6,131
Interest expense, net of capitalized interest	1,382		870		3,817		2,475
Income tax provision (benefit)	1,286		(1,477)		(18,146)		(15,703)
Net financial earnings (loss)	3,865		(1,381)		20,286		9,078
Capital expenditures	46,166		14,891		91,569		39,756
Operating Segments [Member] | Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	3,155		2,563		8,007		7,182
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	1		2		4		5
Interest income	171	[1]	265	[1]	709	[1]	799	[1]
Interest expense, net of capitalized interest	333		466		1,108		1,533
Income tax provision (benefit)	1,321		1,073		3,890		3,935
Equity in earnings of affiliates	3,511		3,052		10,594		11,012
Net financial earnings (loss)	1,896		1,541		5,584		5,600
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	212		196		627		586
Interest income	1	[1]	(1)	[1]	1	[1]	1	[1]
Interest expense, net of capitalized interest	86		261		328		819
Income tax provision (benefit)	1,680		1,378		360		349
Net financial earnings (loss)	2,485		1,944		708		813
Capital expenditures	159		234		636		532
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	13,604		13,470		31,203		32,159
Retail and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	194		234		693		683
Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	(712)		(1,353)		(72,978)		(6,353)
Depreciation and amortization	2		1		0		(1)
Interest income	(241)	[1]	(217)	[1]	(709)	[1]	(667)	[1]
Income tax provision (benefit)	(187)		(410)		201		(234)
Equity in earnings of affiliates	(830)		(830)		(2,538)		(2,705)
Net financial earnings (loss)	$ 14		$ 9		$ 0		$ (12)

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

[2] Includes sales to Canada, which accounted for 3.6 percent and 6.4 percent of total operating revenues during the nine months ended June 30, 2014 and 2013, respectively.