BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) (USD $) In Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2009
Segment Reporting Information [Line Items]
Utility									$ 971,724		$ 937,433		$ 1,082,001
Nonutility									2,037,485		1,701,871		1,510,459
Total operating revenues	670,901	648,169	976,987	713,152	631,518	479,894	918,346	609,546	3,009,209		2,639,304		2,592,460
Depreciation and amortization									34,370		32,267		30,328
Investment Income, Interest									1,216	[1]	2,018	[1]	3,420	[1]
Interest expense, net of capitalized interest									19,623		21,251		21,014
Income tax provision (benefit)									37,665		64,692		11,376
Equity in earnings of affiliates									11,839		10,017		7,153
Net Financial Earnings (Loss)									106,533		101,764		100,970
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets									177,531		97,379		81,634
Payments to Acquire Equity Method Investments									0		4,300		43,843
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total operating revenues									3,024,889		2,630,524		2,580,743
Depreciation and amortization									33,628		31,623		29,622
Investment Income, Interest									2,043	[1]	2,921	[1]	3,872	[1]
Interest expense, net of capitalized interest									19,119		20,477		20,979
Income tax provision (benefit)									36,701		65,558		17,439
Equity in earnings of affiliates									14,904		12,996		6,886
Net Financial Earnings (Loss)									103,446		100,907		99,455
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets									173,982		94,376		81,246
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									33,140		31,464		29,417
Investment Income, Interest									1,133	[1]	1,973	[1]	2,779	[1]
Interest expense, net of capitalized interest									14,875		16,618		18,706
Income tax provision (benefit)									40,322		38,417		39,729
Net Financial Earnings (Loss)									71,322		70,242		65,403
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets									101,993		93,821		81,246
Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility									971,724		937,433		1,082,001
Natural Gas Distribution [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Utility									0		8,047		0
Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									61		153		205
Investment Income, Interest									9	[1]	15	[1]	570	[1]
Interest expense, net of capitalized interest									995		1,439		322
Income tax provision (benefit)									3,281		23,250		(24,259)
Net Financial Earnings (Loss)									18,583		24,814		31,179
Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									1,996,997		1,671,655		1,496,628
Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									55,306		13,389		2,114
Midstream Assets [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									6		6		0
Investment Income, Interest									901	[1]	933	[1]	523	[1]
Interest expense, net of capitalized interest									3,165		2,418		1,951
Income tax provision (benefit)									4,702		4,301		1,969
Equity in earnings of affiliates									14,904		12,996		6,886
Net Financial Earnings (Loss)									6,780		6,444		2,873
Payments to Acquire Equity Method Investments									0		4,300		43,843
Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									421		0		0
Interest expense, net of capitalized interest									84		2		0
Income tax provision (benefit)									(11,604)		(410)		0
Net Financial Earnings (Loss)									6,761		(593)		0
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets									71,989		555		0
Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									862		0		0
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									742		644		706
Investment Income, Interest									43	[1]	4	[1]	44	[1]
Interest expense, net of capitalized interest									504		774		353
Income tax provision (benefit)									1,033		(727)		(5,845)
Net Financial Earnings (Loss)									3,087		857		1,666
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets									3,549		3,003		388
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									39,626		30,216		13,831
Retail and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									334		335		177
Business Intersegment, Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility									(55,640)		(21,771)		(2,291)
Investment Income, Interest									(870)	[1]	(907)	[1]	(496)	[1]
Interest expense, net of capitalized interest									0		0		(318)
Income tax provision (benefit)									(69)		(139)		(218)
Equity in earnings of affiliates									(3,065)		(2,979)		267
Net Financial Earnings (Loss)									$ 0		$ 0		$ (151)

[1] Included in other income in the Consolidated Statement of Operations.