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, 2015		Mar. 31, 2014		Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Utility	$ 374,703		$ 394,528		$ 583,430		$ 627,997
Nonutility	638,387		1,185,041		1,253,784		1,829,977
Total operating revenues	1,013,090		1,579,569		1,837,214		2,457,974
Depreciation and amortization	15,204		12,828		29,590		25,394
Interest income	246	[1]	216	[1]	336	[1]	512	[1]
Interest expense, net of capitalized interest	6,483		6,306		13,678		12,601
Income tax provision (benefit)	20,144		71,680		61,011		73,185
Equity in earnings of affiliates	3,587		3,233		6,382		5,375
Net financial earnings (loss)	99,143		151,920		154,253		191,780
Capital expenditures	66,318		56,242		158,422		116,765
Investments in equity investees	717		0		1,264		0
Canada
Segment Reporting Information [Line Items]
Percentage to total operating revenues					4.40%		4.00%
Midstream Investments [Member]
Segment Reporting Information [Line Items]
Investments in equity investees	717		0		1,264		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total operating revenues	1,060,975		1,638,791		1,879,625		2,512,142
Depreciation and amortization	14,968		12,622		29,128		24,981
Interest income	287	[1]	451	[1]	616	[1]	980	[1]
Interest expense, net of capitalized interest	6,547		6,175		13,736		12,359
Income tax provision (benefit)	20,478		72,255		62,292		74,117
Net financial earnings (loss)	100,524		153,511		156,274		193,572
Capital expenditures	66,268		55,970		158,361		116,288
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	10,647		9,972		21,192		19,807
Interest income	10	[1]	181	[1]	100	[1]	442	[1]
Interest expense, net of capitalized interest	4,388		3,888		8,997		7,872
Income tax provision (benefit)	23,778		23,725		37,944		37,908
Net financial earnings (loss)	48,594		47,043		76,780		74,682
Capital expenditures	33,243		35,484		69,991		70,885
Operating Segments [Member] | Natural Gas Distribution [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Utility	374,703		394,528		583,430		627,997
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	23		13		45		25
Interest income	13	[1]	0	[1]	13	[1]	0	[1]
Interest expense, net of capitalized interest	288		661		801		1,277
Income tax provision (benefit)	3,923		64,345		49,800		53,072
Net financial earnings (loss)	36,316		91,407		52,752		98,781
Operating Segments [Member] | Energy Services [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	626,107	[2]	1,173,835	[2]	1,226,669	[2]	1,807,526	[2]
Operating Segments [Member] | Energy Services [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	56,097		67,749		59,223		71,767
Operating Segments [Member] | Clean Energy Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	4,297		2,635		7,888		5,146
Interest income	22	[1]	0	[1]	22	[1]	0	[1]
Interest expense, net of capitalized interest	1,661		1,249		3,478		2,435
Income tax provision (benefit)	(9,042)		(17,388)		(28,763)		(19,432)
Net financial earnings (loss)	13,010		12,807		22,018		16,421
Capital expenditures	33,025		20,486		88,370		45,403
Operating Segments [Member] | Clean Energy Ventures [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	4,068		2,679		10,303		4,852
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	1		2		3		3
Interest income	242	[1]	270	[1]	481	[1]	538	[1]
Interest expense, net of capitalized interest	210		377		460		775
Income tax provision (benefit)	1,819		1,573		3,311		2,569
Equity in earnings of affiliates	4,581		4,141		8,356		7,083
Net financial earnings (loss)	2,604		2,254		4,724		3,688
Home Services and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	238		208		476		415
Interest income	201	[1]	0	[1]	201	[1]	0	[1]
Interest expense, net of capitalized interest	(64)		131		(58)		242
Income tax provision (benefit)	(972)		(1,129)		(1,424)		(1,320)
Net financial earnings (loss)	(1,359)		(1,576)		(1,951)		(1,777)
Capital expenditures	50		272		61		477
Home Services and Other [Member] | External Customers [Member]
Segment Reporting Information [Line Items]
Nonutility	8,212		8,527		16,812		17,599
Home Services and Other [Member] | Intercompany [Member]
Segment Reporting Information [Line Items]
Nonutility	375		297		786		499
Eliminations [Member]
Segment Reporting Information [Line Items]
Nonutility	(56,472)		(68,046)		(60,009)		(72,266)
Depreciation and amortization	(2)		(2)		(14)		(2)
Interest income	(242)	[1]	(235)	[1]	(481)	[1]	(468)	[1]
Income tax provision (benefit)	638		554		143		388
Equity in earnings of affiliates	(994)		(908)		(1,974)		(1,708)
Net financial earnings (loss)	$ (22)		$ (15)		$ (70)		$ (15)

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

[2] Includes sales to Canada, which accounted for 4.4 percent and 4 percent of total operating revenues during the six months ended March 31, 2015 and 2014, respectively.