Business Segment Information (Segment Information By Segment) (Details) - USD ($) $ in Thousands		3 Months Ended															12 Months Ended
		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Interest Income																	$ 4,235	$ 3,922	$ 4,170
Interest Expense																	121,044	99,471	94,277
Depreciation, Depletion and Amortization																	249,417	336,158	383,781
Income Tax Expense (Benefit)																	(232,549)	(319,136)	189,614
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties		$ 32,700		$ 82,700		$ 397,400		$ 435,500		$ 417,200		$ 588,700		$ 120,300			948,307	1,126,257	0
Segment Profit: Net Income (Loss)		37,553	[1]	$ 8,286	[2]	$ (147,688)	[3]	$ (189,109)	[4]	(187,703)	[5]	$ (293,134)	[6]	$ 16,669	[7]	$ 84,741	(290,958)	(379,427)	299,413
Expenditures for Additions to Long-Lived Assets																	523,051	1,000,509	969,907
Segment Assets		5,636,387								6,564,939							5,636,387	6,564,939	6,687,717
Utility [Member]
Segment Reporting Information [Line Items]
Interest Income																	1,737	2,220	3,010
Interest Expense																	27,582	28,176	27,693
Depreciation, Depletion and Amortization																	48,618	45,616	43,594
Income Tax Expense (Benefit)																	25,602	33,143	33,918
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	50,960	63,271	64,059
Expenditures for Additions to Long-Lived Assets																	98,007	94,371	88,810
Segment Assets		2,021,514								1,934,731							2,021,514	1,934,731	1,841,891
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Interest Income																	770	474	284
Interest Expense																	33,327	27,658	26,428
Depreciation, Depletion and Amortization																	43,273	38,178	36,642
Income Tax Expense (Benefit)																	50,241	48,113	47,100
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	76,610	80,354	77,559
Expenditures for Additions to Long-Lived Assets																	114,250	230,192	139,821
Segment Assets		1,680,734								1,590,524							1,680,734	1,590,524	1,364,659
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Interest Income																	858	2,554	1,909
Interest Expense																	55,434	46,726	42,232
Depreciation, Depletion and Amortization																	139,963	239,818	296,210
Income Tax Expense (Benefit)																	(334,029)	(428,217)	81,370
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	948,307	1,126,257
Segment Profit: Net Income (Loss)																	(452,842)	(556,974)	121,569
Expenditures for Additions to Long-Lived Assets																	256,104	557,313	602,705
Segment Assets		1,323,081								2,439,801							1,323,081	2,439,801	3,081,885
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Interest Income																	422	195	173
Interest Expense																	49	27	31
Depreciation, Depletion and Amortization																	278	209	197
Income Tax Expense (Benefit)																	2,460	4,547	3,761
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	4,348	7,766	6,631
Expenditures for Additions to Long-Lived Assets																	34	128	264
Segment Assets		63,392								90,676							63,392	90,676	77,152
Gathering [Member]
Segment Reporting Information [Line Items]
Interest Income																	297	140	120
Interest Expense																	8,872	1,627	1,726
Depreciation, Depletion and Amortization																	15,282	10,829	6,116
Income Tax Expense (Benefit)																	24,334	24,721	23,636
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	30,499	31,849	32,709
Expenditures for Additions to Long-Lived Assets																	54,293	118,166	137,799
Segment Assets		534,259								444,358							534,259	444,358	325,388
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Interest Income																	4,084	5,583	5,496
Interest Expense																	125,264	104,214	98,110
Depreciation, Depletion and Amortization																	247,414	334,650	382,759
Income Tax Expense (Benefit)																	(231,392)	(317,693)	189,785
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	948,307	1,126,257
Segment Profit: Net Income (Loss)																	(290,425)	(373,734)	302,527
Expenditures for Additions to Long-Lived Assets																	522,688	1,000,170	969,399
Segment Assets		5,622,980								6,500,090							5,622,980	6,500,090	6,690,975
All Other [Member]
Segment Reporting Information [Line Items]
Interest Income																	117	66	106
Interest Expense																	0	0	6
Depreciation, Depletion and Amortization																	1,260	832	344
Income Tax Expense (Benefit)																	561	13	822
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	778	(2)	1,160
Expenditures for Additions to Long-Lived Assets																	37	0	274
Segment Assets		77,138								77,350							77,138	77,350	89,760
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Interest Income																	34	(1,727)	(1,432)
Interest Expense																	(4,220)	(4,743)	(3,839)
Depreciation, Depletion and Amortization																	743	676	678
Income Tax Expense (Benefit)																	(1,718)	(1,456)	(993)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties																	0	0
Segment Profit: Net Income (Loss)																	(1,311)	(5,691)	(4,274)
Expenditures for Additions to Long-Lived Assets																	326	339	234
Segment Assets		$ (63,731)								$ (12,501)							(63,731)	(12,501)	(93,018)
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																1,452,416	1,760,913	2,113,081
Revenue from External Customers [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																531,024	700,761	831,156
Revenue from External Customers [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																215,674	203,089	200,664
Revenue from External Customers [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																607,113	693,441	804,096
Revenue from External Customers [Member] | Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																93,578	159,857	271,993
Revenue from External Customers [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																374	497	673
Revenue from External Customers [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																1,447,763	1,757,645	2,108,582
Revenue from External Customers [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																3,753	2,352	3,532
Revenue from External Customers [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	[8]																900	916	967
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue																	0	0	0
Intersegment Revenues [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue																	13,123	15,506	18,462
Intersegment Revenues [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue																	90,755	88,251	83,744
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																	884	849	1,159
Intersegment Revenues [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue																	89,073	76,709	69,937
Intersegment Revenues [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue																	193,835	181,315	173,302
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																	$ (193,835)	$ (181,315)	$ (173,302)

[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] Includes a non-cash $417.2 million impairment charge ($240.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $8.0 million reversal of stock-based compensation expense ($4.7 million after tax) related to performance based restricted stock units.

[6] Includes a non-cash $588.7 million impairment charge ($339.8 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[7] Includes a non-cash $120.3 million impairment charge ($69.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

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