Business Segment Information (Segment Information By Segment) (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]
Interest Income											$ 4,170		$ 4,335		$ 3,689
Interest Expense											94,277		94,111		86,240
Depreciation, Depletion and Amortization											383,781		326,760		271,530
Income Tax Expense (Benefit)											189,614		172,758		150,554
Segment Profit: Net Income (Loss)	57,431	64,520	95,210	[1]	82,252	47,842	[2]	58,495	85,720	67,944	299,413		260,001		220,077
Expenditures for Additions to Long-Lived Assets											969,907		717,097		977,394
Segment Assets	6,739,597					6,218,347					6,739,597		6,218,347		5,935,142
Utility [Member]
Segment Reporting Information [Line Items]
Interest Income											3,010		3,417		2,765
Interest Expense											27,693		29,076		33,181
Depreciation, Depletion and Amortization											43,594		42,729		42,757
Income Tax Expense (Benefit)											33,918		31,065		29,110
Segment Profit: Net Income (Loss)											64,059		65,686		58,590
Expenditures for Additions to Long-Lived Assets											88,810		71,970		58,284
Segment Assets	1,862,850					1,870,587					1,862,850		1,870,587		2,070,413
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Interest Income											284		193		199
Interest Expense											26,428		26,248		25,603
Depreciation, Depletion and Amortization											36,642		35,156		38,182
Income Tax Expense (Benefit)											47,100		38,626		37,655
Segment Profit: Net Income (Loss)											77,559		63,245		60,527
Expenditures for Additions to Long-Lived Assets											139,821		56,144		144,167
Segment Assets	1,367,181					1,246,027					1,367,181		1,246,027		1,243,862
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Interest Income											1,909		1,501		1,493
Interest Expense											42,232		39,745		29,243
Depreciation, Depletion and Amortization											296,210		243,431		187,624
Income Tax Expense (Benefit)											81,370		95,317		79,050
Segment Profit: Net Income (Loss)											121,569		115,391		96,498
Expenditures for Additions to Long-Lived Assets											602,705		533,129		693,810
Segment Assets	3,100,514					2,746,233					3,100,514		2,746,233		2,367,485
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Interest Income											173		169		188
Interest Expense											31		36		41
Depreciation, Depletion and Amortization											197		123		90
Income Tax Expense (Benefit)											3,761		2,450		1,933
Segment Profit: Net Income (Loss)											6,631		4,589		4,169
Expenditures for Additions to Long-Lived Assets											264		595		770
Segment Assets	76,238					67,267					76,238		67,267		61,968
Gathering [Member]
Segment Reporting Information [Line Items]
Interest Income											120		55		1
Interest Expense											1,726		2,283		1,444
Depreciation, Depletion and Amortization											6,116		3,945		1,691
Income Tax Expense (Benefit)											23,636		10,287		4,825
Segment Profit: Net Income (Loss)											32,709		13,321		6,855
Expenditures for Additions to Long-Lived Assets											137,799		54,792		80,012
Segment Assets	326,662					203,323					326,662		203,323		116,756
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Interest Income											5,496		5,335		4,646
Interest Expense											98,110		97,388		89,512
Depreciation, Depletion and Amortization											382,759		325,384		270,344
Income Tax Expense (Benefit)											189,785		177,745		152,573
Segment Profit: Net Income (Loss)											302,527		262,232		226,639
Expenditures for Additions to Long-Lived Assets											969,399		716,630		977,043
Segment Assets	6,733,445					6,133,437					6,733,445		6,133,437		5,860,484
All Other [Member]
Segment Reporting Information [Line Items]
Interest Income											106		115		174
Interest Expense											6		2		294
Depreciation, Depletion and Amortization											344		577		400
Income Tax Expense (Benefit)											822		529		(490)
Segment Profit: Net Income (Loss)											1,160		894		13
Expenditures for Additions to Long-Lived Assets											274		307		5
Segment Assets	86,460					95,793					86,460		95,793		93,178
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Interest Income											(1,432)		(1,115)		(1,131)
Interest Expense											(3,839)		(3,279)		(3,566)
Depreciation, Depletion and Amortization											678		799		786
Income Tax Expense (Benefit)											(993)		(5,516)		(1,529)
Segment Profit: Net Income (Loss)											(4,274)		(3,125)		(6,575)
Expenditures for Additions to Long-Lived Assets											234		160		346
Segment Assets	(80,308)					(10,883)					(80,308)		(10,883)		(18,520)
Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue											2,113,081	[3]	1,829,551	[3]	1,626,853	[3]
Revenue From External Customers [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue											831,156	[3]	730,319	[3]	704,518	[3]
Revenue From External Customers [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue											200,664	[3]	178,184	[3]	172,312	[3]
Revenue From External Customers [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue											804,096	[3]	702,937	[3]	558,180	[3]
Revenue From External Customers [Member] | Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue											271,993	[3]	211,990	[3]	186,579	[3]
Revenue From External Customers [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue											673	[3]	1,324	[3]	704	[3]
Revenue From External Customers [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue											2,108,582	[3]	1,824,754	[3]	1,622,293	[3]
Revenue From External Customers [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue											3,532	[3]	3,910	[3]	3,603	[3]
Revenue From External Customers [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue											967	[3]	887	[3]	957	[3]
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											0		0		0
Intersegment Revenues [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue											18,462		16,020		14,604
Intersegment Revenues [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue											83,744		89,424		86,963
Intersegment Revenues [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue											0		0		0
Intersegment Revenues [Member] | Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue											1,159		1,384		1,425
Intersegment Revenues [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue											69,937		33,457		16,771
Intersegment Revenues [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue											173,302		140,285		119,763
Intersegment Revenues [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue											0		0		0
Intersegment Revenues [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue											$ (173,302)		$ (140,285)		$ (119,763)

[1] Includes $3.6 million of income associated with a death benefit gain on life insurance proceeds recorded in the Corporate category.

[2] Includes a $4.7 million refund provision recorded in the Utility segment related to various issues raised in Distribution Corporation’s rate proceeding in New York.

[3] All Revenue from External Customers originated in the United States.