BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Segment Reporting Information [Line Items]
Utility									$ 787,987		$ 627,713		$ 971,724
Nonutility									2,410,081		1,621,210		2,037,485
Total operating revenues	733,695	767,469	960,885	736,019	568,470	425,121	612,921	642,411	3,198,068		2,248,923		3,009,209
Depreciation and amortization									47,310		41,643		34,370
Interest income									837	[1]	1,026	[1]	1,216	[1]
Interest expense, net of capitalized interest									23,979		20,844		19,623
Income tax provision (benefit)									35,575		7,729		37,665
Equity in earnings of affiliates									10,349		10,634		11,839
Net financial earnings									113,681		112,417		106,533
Capital expenditures									197,250		207,515		177,531
Investments in equity investees									0		8,800		0
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total operating revenues									3,156,553		2,210,581		3,024,889
Depreciation and amortization									46,526		40,992		33,628
Interest income									1,719	[1]	2,024	[1]	2,043	[1]
Interest expense, net of capitalized interest									22,878		19,505		19,119
Income tax provision (benefit)									33,197		5,656		36,701
Net financial earnings									110,416		110,230		103,446
Capital expenditures									196,208		206,181		173,982
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									37,999		35,247		33,140
Interest income									653	[1]	889	[1]	1,133	[1]
Interest expense, net of capitalized interest									14,995		14,890		14,875
Income tax provision (benefit)									35,399		38,135		40,322
Net financial earnings									73,846		73,238		71,322
Capital expenditures									137,083		116,455		101,993
Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility									787,987		627,713		971,724
Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									44		59		61
Interest income									1	[1]	37	[1]	9	[1]
Interest expense, net of capitalized interest									2,534		1,096		995
Income tax provision (benefit)									10,516		(4,950)		3,281
Net financial earnings									19,311		10,791		18,583
Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									2,351,084	[2]	1,577,851	[2]	1,996,997	[2]
Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									5,494		2,760		55,306
Midstream [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									6		6		6
Interest income									1,065	[1]	1,098	[1]	901	[1]
Interest expense, net of capitalized interest									1,962		2,665		3,165
Income tax provision (benefit)									4,993		4,978		4,702
Equity in earnings of affiliates									13,868		14,308		14,904
Net financial earnings									7,199		6,749		6,780
Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									8,477		5,680		421
Interest expense, net of capitalized interest									3,387		854		84
Income tax provision (benefit)									(17,711)		(32,507)		(11,604)
Net financial earnings									10,060		19,452		6,761
Capital expenditures									59,125		89,726		71,989
Investments in equity investees									0		8,800		0
Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									11,988		2,257		862
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									786		661		742
Interest income									2	[1]	3	[1]	43	[1]
Interest expense, net of capitalized interest									1,101		1,339		504
Income tax provision (benefit)									2,550		2,178		1,033
Net financial earnings									3,292		2,366		3,087
Capital expenditures									1,042		1,334		3,549
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									47,009		41,102		39,626
Retail and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									945		1,093		334
Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility									(6,439)		(3,853)		(55,640)
Depreciation and amortization									(2)		(10)		0
Interest income									(884)	[1]	(1,001)	[1]	(870)	[1]
Income tax provision (benefit)									(172)		(105)		(69)
Equity in earnings of affiliates									(3,519)		(3,674)		(3,065)
Net financial earnings									$ (27)		$ (179)		$ 0
Canada
Segment Reporting Information [Line Items]
Percentage to total operating revenues									5.90%		6.60%		6.10%

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

[2] Includes sales to Canada, which accounted for 5.9 percent, 6.6 percent and 6.1 percent of total operating revenues during fiscal 2013, 2012 and 2011, respectively.