Business Segment Information (Segment Information By Segment) (Details) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Interest Income														$ 4,113	$ 4,235	$ 3,922
Interest Expense														119,837	121,044	99,471
Depreciation, Depletion and Amortization														224,195	249,417	336,158
Income Tax Expense (Benefit)														160,682	(232,549)	(319,136)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties						$ 32,700		$ 82,700		$ 397,400		$ 435,500		0	948,307	1,126,257
Segment Profit: Net Income (Loss)		$ 45,577	$ 59,714	$ 89,283	$ 88,908	37,553	[1]	$ 8,286	[2]	$ (147,688)	[3]	$ (189,109)	[4]	283,482	(290,958)	(379,427)
Expenditures for Additions to Long-Lived Assets														462,117	523,051	1,000,509
Segment Assets		6,103,320				5,636,387								6,103,320	5,636,387	6,564,939
Utility [Member]
Segment Reporting Information [Line Items]
Interest Income														1,051	1,737	2,220
Interest Expense														28,492	27,582	28,176
Depreciation, Depletion and Amortization														52,582	48,618	45,616
Income Tax Expense (Benefit)														24,894	25,602	33,143
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														46,935	50,960	63,271
Expenditures for Additions to Long-Lived Assets														80,867	98,007	94,371
Segment Assets		2,013,123				2,021,514								2,013,123	2,021,514	1,934,731
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Interest Income														1,467	770	474
Interest Expense														33,717	33,327	27,658
Depreciation, Depletion and Amortization														41,196	43,273	38,178
Income Tax Expense (Benefit)														40,947	50,241	48,113
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														68,446	76,610	80,354
Expenditures for Additions to Long-Lived Assets														95,336	114,250	230,192
Segment Assets		1,929,788				1,680,734								1,929,788	1,680,734	1,590,524
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Interest Income														707	858	2,554
Interest Expense														53,702	55,434	46,726
Depreciation, Depletion and Amortization														112,565	139,963	239,818
Income Tax Expense (Benefit)														66,093	(334,029)	(428,217)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															948,307	1,126,257
Segment Profit: Net Income (Loss)														129,326	(452,842)	(556,974)
Expenditures for Additions to Long-Lived Assets														253,057	256,104	557,313
Segment Assets		1,407,152				1,323,081								1,407,152	1,323,081	2,439,801
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Interest Income														571	422	195
Interest Expense														47	49	27
Depreciation, Depletion and Amortization														279	278	209
Income Tax Expense (Benefit)														891	2,460	4,547
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														1,509	4,348	7,766
Expenditures for Additions to Long-Lived Assets														36	34	128
Segment Assets		60,937				63,392								60,937	63,392	90,676
Gathering [Member]
Segment Reporting Information [Line Items]
Interest Income														994	297	140
Interest Expense														9,142	8,872	1,627
Depreciation, Depletion and Amortization														16,162	15,282	10,829
Income Tax Expense (Benefit)														29,694	24,334	24,721
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														40,377	30,499	31,849
Expenditures for Additions to Long-Lived Assets														32,645	54,293	118,166
Segment Assets		580,051				534,259								580,051	534,259	444,358
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Interest Income														4,790	4,084	5,583
Interest Expense														125,100	125,264	104,214
Depreciation, Depletion and Amortization														222,784	247,414	334,650
Income Tax Expense (Benefit)														162,519	(231,392)	(317,693)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															948,307	1,126,257
Segment Profit: Net Income (Loss)														286,593	(290,425)	(373,734)
Expenditures for Additions to Long-Lived Assets														461,941	522,688	1,000,170
Segment Assets		5,991,051				5,622,980								5,991,051	5,622,980	6,500,090
All Other [Member]
Segment Reporting Information [Line Items]
Interest Income														213	117	66
Interest Expense														0	0	0
Depreciation, Depletion and Amortization														661	1,260	832
Income Tax Expense (Benefit)														(247)	561	13
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														(342)	778	(2)
Expenditures for Additions to Long-Lived Assets														39	37	0
Segment Assets		76,861				77,138								76,861	77,138	77,350
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Interest Income														(890)	34	(1,727)
Interest Expense														(5,263)	(4,220)	(4,743)
Depreciation, Depletion and Amortization														750	743	676
Income Tax Expense (Benefit)														(1,590)	(1,718)	(1,456)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties															0	0
Segment Profit: Net Income (Loss)														(2,769)	(1,311)	(5,691)
Expenditures for Additions to Long-Lived Assets														137	326	339
Segment Assets		$ 35,408				$ (63,731)								35,408	(63,731)	(12,501)
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													1,579,881	1,452,416	1,760,913
Revenue from External Customers [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													626,899	531,024	700,761
Revenue from External Customers [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													206,615	215,674	203,089
Revenue from External Customers [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													614,599	607,113	693,441
Revenue from External Customers [Member] | Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													128,586	93,578	159,857
Revenue from External Customers [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													115	374	497
Revenue from External Customers [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													1,576,814	1,447,763	1,757,645
Revenue from External Customers [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													2,173	3,753	2,352
Revenue from External Customers [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													894	900	916
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue														0	0	0
Intersegment Revenues [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue														13,072	13,123	15,506
Intersegment Revenues [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue														87,810	90,755	88,251
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														794	884	849
Intersegment Revenues [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue														107,566	89,073	76,709
Intersegment Revenues [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue														209,242	193,835	181,315
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														$ (209,242)	$ (193,835)	$ (181,315)

[1] Includes a non-cash $32.7 million impairment charge ($19.0 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[2] Includes a non-cash $82.7 million impairment charge ($47.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $397.4 million impairment charge ($230.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[4] Includes a non-cash $435.5 million impairment charge ($252.6 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

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