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, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Segment Reporting Information [Line Items]
Utility									$ 819,415		$ 787,987		$ 627,713
Nonutility									2,918,730		2,410,081		1,621,210
Total operating revenues	591,914	688,257	1,579,569	878,405	733,695	767,469	960,885	736,019	3,738,145		3,198,068		2,248,923
Depreciation and amortization									52,742		47,310		41,643
Interest income									1,222	[1]	837	[1]	1,026	[1]
Interest expense, net of capitalized interest									25,463		23,979		20,844
Income tax provision (benefit)									51,840		35,575		7,729
Equity in earnings of affiliates									10,532		10,349		10,634
Net financial earnings									176,857		113,681		112,417
Capital expenditures									289,288		197,250		207,515
Investments in equity investees									555		0		8,800
Investments in equity investees									555		0		8,800
Canada
Segment Reporting Information [Line Items]
Percentage to total operating revenues									3.30%		5.90%		6.60%
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total operating revenues									3,764,807		3,156,553		2,210,581
Depreciation and amortization									51,900		46,526		40,992
Interest income									2,171	[1]	1,719	[1]	2,024	[1]
Interest expense, net of capitalized interest									25,104		22,878		19,505
Income tax provision (benefit)									49,122		33,197		5,656
Net financial earnings									174,091		110,416		110,230
Capital expenditures									288,109		196,208		206,181
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									40,540		37,999		35,247
Interest income									999	[1]	653	[1]	889	[1]
Interest expense, net of capitalized interest									16,683		14,995		14,890
Income tax provision (benefit)									39,374		35,399		38,135
Net financial earnings									74,204		73,846		73,238
Capital expenditures									152,566		137,083		116,455
Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility									819,415		787,987		627,713
Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									59		44		59
Interest income									222	[1]	1	[1]	37	[1]
Interest expense, net of capitalized interest									1,725		2,534		1,096
Income tax provision (benefit)									26,458		10,516		(4,950)
Net financial earnings									79,735		19,311		10,791
Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									2,858,703	[2]	2,351,084	[2]	1,577,851	[2]
Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									72,114		5,494		2,760
Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									11,295		8,477		5,680
Interest expense, net of capitalized interest									5,300		3,387		854
Income tax provision (benefit)									(21,937)		(17,711)		(32,507)
Net financial earnings									12,654		10,060		19,452
Capital expenditures									135,543		59,125		89,726
Investments in equity investees									0		0		8,800
Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									14,575		11,988		2,257
Midstream [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									6		6		6
Interest income									950	[1]	1,065	[1]	1,098	[1]
Interest expense, net of capitalized interest									1,396		1,962		2,665
Income tax provision (benefit)									5,227		4,993		4,978
Equity in earnings of affiliates									14,078		13,868		14,308
Net financial earnings									7,498		7,199		6,749
Investments in equity investees									555		0		0
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									846		786		661
Interest income									1	[1]	2	[1]	3	[1]
Interest expense, net of capitalized interest									359		1,101		1,339
Income tax provision (benefit)									2,460		2,550		2,178
Net financial earnings									2,798		3,292		2,366
Capital expenditures									1,179		1,042		1,334
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility									45,452		47,009		41,102
Retail and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility									1,235		945		1,093
Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility									(73,349)		(6,439)		(3,853)
Depreciation and amortization									(4)		(2)		(10)
Interest income									(950)	[1]	(884)	[1]	(1,001)	[1]
Income tax provision (benefit)									258		(172)		(105)
Equity in earnings of affiliates									(3,546)		(3,519)		(3,674)
Net financial earnings									$ (32)		$ (27)		$ (179)

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

[2] Includes sales to Canada, which accounted for 3.3, 5.9 and 6.6 percent of total operating revenues during fiscal 2014, 2013 and 2012, respectively.