Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 89,284	$ (147,687)	$ 178,191	$ (336,796)
Segment Assets	5,804,675		5,804,675		$ 5,636,387
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	522,075	449,132	944,576	824,327
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	33,769	(213,335)	68,849	(450,421)
Segment Assets	1,292,230		1,292,230		1,323,081
Exploration And Production [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	159,553	143,783	320,485	295,749
Exploration And Production [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	19,256	21,194	38,624	42,470
Segment Assets	1,718,862		1,718,862		1,680,734
Pipeline And Storage [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	53,163	56,276	106,164	109,630
Pipeline And Storage [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	22,592	23,292	44,746	45,477
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	10,285	7,568	21,266	12,490
Segment Assets	553,719		553,719		534,259
Gathering [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	26	113	52	238
Gathering [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	27,936	21,545	55,776	40,184
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	25,581	31,960	46,755	50,566
Segment Assets	2,108,549		2,108,549		2,021,514
Utility [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	257,949	212,737	428,919	356,585
Utility [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	6,096	5,364	7,922	9,028
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	905	3,484	2,687	4,707
Segment Assets	74,404		74,404		63,392
Energy Marketing [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	50,940	35,436	87,750	60,420
Energy Marketing [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	16	312	35	624
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	89,796	(149,129)	178,181	(340,188)
Segment Assets	5,747,764		5,747,764		5,622,980
Total Reportable Segments [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	521,631	448,345	943,370	822,622
Total Reportable Segments [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	56,640	50,513	108,479	95,313
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(221)	(23)	(400)	166
Segment Assets	76,630		76,630		77,138
All Other [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	218	561	772	1,266
All Other [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(291)	1,465	410	3,226
Segment Assets	(19,719)		(19,719)		$ (63,731)
Corporate And Intersegment Eliminations [Member] \| Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	226	226	434	439
Corporate And Intersegment Eliminations [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (56,640)	$ (50,513)	$ (108,479)	$ (95,313)