BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Mar. 31, 2012		Mar. 31, 2011
Segment Reporting Information [Line Items]
Utility	$ 226,023		$ 433,248		$ 417,397		$ 723,924
Nonutility	386,898		543,739		837,935		966,215
Total operating revenues	612,921		976,987		1,255,332		1,690,139
Depreciation and amortization	10,439		8,477		20,039		16,931
Investment Income, Interest	227	[1]	291	[1]	517	[1]	563	[1]
Interest expense, net of capitalized interest	5,427		5,078		10,432		10,341
Income tax provision (benefit)	11,094		28,612		27,131		42,465
Equity in earnings of affiliates	3,018		3,610		5,672		6,527
Net Financial Earnings (Loss)	74,126		67,029		119,434		96,159
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets	41,972		29,743		111,390		59,086
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total operating revenues	607,560		1,006,323		1,241,314		1,727,773
Depreciation and amortization	10,278		8,280		19,737		16,520
Investment Income, Interest	494	[1]	507	[1]	1,019	[1]	1,000	[1]
Interest expense, net of capitalized interest	4,839		4,951		9,702		10,055
Income tax provision (benefit)	11,478		29,219		27,642		43,522
Equity in earnings of affiliates	3,967		4,360		7,582		7,980
Net Financial Earnings (Loss)	74,690		67,357		120,159		96,647
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets	41,602		28,026		110,931		57,123
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	8,749		8,235		17,381		16,458
Investment Income, Interest	214	[1]	280	[1]	460	[1]	540	[1]
Interest expense, net of capitalized interest	3,713		3,808		7,450		7,824
Income tax provision (benefit)	27,016		26,278		42,612		40,879
Net Financial Earnings (Loss)	44,936		44,040		70,910		68,396
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets	27,427		18,988		49,145		47,186
Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility	226,023		433,248		417,397		723,924
Natural Gas Distribution [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Utility	0		0		0		0
Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	16		15		32		31
Investment Income, Interest	(5)	[1]	3	[1]	26	[1]	8	[1]
Interest expense, net of capitalized interest	245		323		515		599
Income tax provision (benefit)	(2,105)		7,525		9,403		6,683
Net Financial Earnings (Loss)	15,871		16,001		23,486		19,168
Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	378,356		535,987		820,162		950,418
Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	2,654		37,088		2,848		53,431
Energy Holdings [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2		2		3		3
Investment Income, Interest	285	[1]	224	[1]	533	[1]	452	[1]
Interest expense, net of capitalized interest	683		817		1,397		1,625
Income tax provision (benefit)	1,393		1,487		2,624		2,670
Equity in earnings of affiliates	3,967		4,360		7,582		7,980
Net Financial Earnings (Loss)	2,021		2,145		3,804		3,858
Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	1,511		28		2,321		28
Interest expense, net of capitalized interest	198		3		340		7
Income tax provision (benefit)	(14,826)		(6,071)		(26,997)		(6,710)
Net Financial Earnings (Loss)	11,862		5,171		21,959		5,225
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets	14,175		9,038		61,786		9,937
Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	527		0		907		0
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	161		197		302		411
Investment Income, Interest	1	[1]	1	[1]	1	[1]	1	[1]
Interest expense, net of capitalized interest	588		127		730		286
Income tax provision (benefit)	(312)		(588)		(371)		(1,044)
Net Financial Earnings (Loss)	(543)		(328)		(689)		(488)
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets	370		1,717		459		1,963
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	8,014		7,751		16,866		15,796
Retail and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	263		75		442		156
Business Intersegment, Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	(2,916)		(37,162)		(3,290)		(53,586)
Investment Income, Interest	(268)	[1]	(217)	[1]	(503)	[1]	(438)	[1]
Income tax provision (benefit)	(72)		(19)		(140)		(13)
Equity in earnings of affiliates	(949)		(750)		(1,910)		(1,453)
Net Financial Earnings (Loss)	$ (21)		$ 0		$ (36)		$ 0

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