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, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Segment Reporting Information [Line Items]
Utility	$ 119,022		$ 106,764		$ 689,621		$ 524,161
Nonutility	648,447		318,357		1,774,752		1,156,292
Total operating revenues	767,469		425,121		2,464,373		1,680,453
Depreciation and amortization	11,942		10,687		34,966		30,726
Interest income	193	[1]	253	[1]	592	[1]	770	[1]
Interest expense, net of capitalized interest	6,008		4,834		17,579		15,266
Income tax provision (benefit)	15,297		(11,230)		51,342		15,901
Equity in earnings of affiliates	2,222		2,644		8,307		8,316
Net financial earnings (loss)	9,738		4,130		113,895		123,564
Capital expenditures	44,266		46,971		135,128		158,361
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	9,537		8,860		28,213		26,241
Interest income	146	[1]	223	[1]	459	[1]	683	[1]
Interest expense, net of capitalized interest	3,796		3,717		10,929		11,167
Income tax provision (benefit)	1,788		1,114		39,089		43,726
Net financial earnings (loss)	5,528		7,545		76,937		78,455
Capital expenditures	29,141		33,405		94,840		82,550
Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility	119,022		106,764		689,621		524,161
Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2,196		1,632		6,131		3,953
Interest expense, net of capitalized interest	870		190		2,475		530
Income tax provision (benefit)	(1,477)		(3,013)		(15,703)		(30,010)
Net financial earnings (loss)	(1,381)		(1,157)		9,078		20,802
Capital expenditures	14,891		13,457		39,756		75,243
Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	2,563		370		7,182		1,277
Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	10		16		32		48
Interest income	0	[1]	10	[1]	0	[1]	36	[1]
Interest expense, net of capitalized interest	615		214		1,823		729
Income tax provision (benefit)	12,945		(11,511)		23,906		(2,108)
Net financial earnings (loss)	2,097		(5,425)		21,479		18,061
Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	632,414		306,273		1,735,411		1,126,435
Energy Services [Member] | Intercompany/Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	1,119		(32)		5,670		2,816
Midstream Investments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2		1		5		4
Interest income	265	[1]	267	[1]	799	[1]	800	[1]
Interest expense, net of capitalized interest	466		653		1,533		2,050
Income tax provision (benefit)	1,073		1,126		3,935		3,750
Equity in earnings of affiliates	3,052		3,547		11,012		11,129
Net financial earnings (loss)	1,541		1,634		5,600		5,438
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total operating revenues	755,118		413,375		2,437,884		1,654,689
Depreciation and amortization	11,745		10,509		34,381		30,246
Interest income	411	[1]	500	[1]	1,258	[1]	1,519	[1]
Interest expense, net of capitalized interest	5,747		4,774		16,760		14,476
Income tax provision (benefit)	14,329		(12,284)		51,227		15,358
Net financial earnings (loss)	7,785		2,597		113,094		122,756
Capital expenditures	44,032		46,862		134,596		157,793
Retail and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	196		178		586		480
Interest income	(1)	[1]	1	[1]	1	[1]	2	[1]
Interest expense, net of capitalized interest	261		60		819		790
Income tax provision (benefit)	1,378		1,056		349		685
Net financial earnings (loss)	1,944		1,549		813		860
Capital expenditures	234		109		532		568
Retail and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	13,470		11,714		32,159		28,580
Retail and Other [Member] | Intercompany/Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	234		278		683		720
Intercompany/Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	(1,353)		(246)		(6,353)		(3,536)
Depreciation and amortization	1		0		(1)		0
Interest income	(217)	[1]	(248)	[1]	(667)	[1]	(751)	[1]
Income tax provision (benefit)	(410)		(2)		(234)		(142)
Equity in earnings of affiliates	(830)		(903)		(2,705)		(2,813)
Net financial earnings (loss)	$ 9		$ (16)		$ (12)		$ (52)

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