Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2015
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ (147,687)	$ 16,669	$ (336,796)	$ 101,409
Segment Assets	5,801,024		5,801,024		$ 6,564,939
Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	449,132	596,127	824,327	1,120,036
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)	(213,335)	(53,562)	(450,421)	(26,842)
Segment Assets	1,622,264		1,622,264		2,439,801
Exploration And Production [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	143,783	165,521	295,749	370,186
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)	21,194	23,377	42,470	44,155
Segment Assets	1,664,920		1,664,920		1,590,525
Pipeline And Storage [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	56,276	55,758	109,630	107,504
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	23,292	23,054	45,477	44,515
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	7,568	6,405	12,490	18,028
Segment Assets	487,421		487,421		444,358
Gathering [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	113	89	238	235
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	21,545	17,365	40,184	41,793
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	31,960	38,238	50,566	60,831
Segment Assets	1,984,921		1,984,921		1,934,730
Utility [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	212,737	309,974	356,585	520,047
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	5,364	6,521	9,028	11,055
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	3,484	3,373	4,707	6,199
Segment Assets	91,671		91,671		90,676
Energy Marketing [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	35,436	64,167	60,420	120,333
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	312	211	624	417
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(149,129)	17,831	(340,188)	102,371
Segment Assets	5,851,197		5,851,197		6,500,090
Total Reportable Segments [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	448,345	595,509	822,622	1,118,305
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	50,513	47,151	95,313	97,780
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(23)	98	166	93
Segment Assets	77,689		77,689		77,350
All Other [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	561	388	1,266	1,271
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)	1,465	(1,260)	3,226	(1,055)
Segment Assets	(127,862)		(127,862)		$ (12,501)
Corporate And Intersegment Eliminations [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	226	230	439	460
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (50,513)	$ (47,151)	$ (95,313)	$ (97,780)