Business Segment Information (Financial Segment Information By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2014
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 84,740	$ 82,252
Segment Assets	7,145,094		6,739,597
Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	523,909	550,072
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	26,720	31,097
Segment Assets	3,346,609		3,100,514
Exploration And Production [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	204,665	193,046
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	20,778	19,138
Segment Assets	1,400,955		1,367,181
Pipeline And Storage [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	51,745	51,212
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	21,461	20,739
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	11,623	6,147
Segment Assets	352,464		326,662
Gathering [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	146	235
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	24,428	14,350
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	22,594	24,215
Segment Assets	1,942,168		1,862,850
Utility [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	210,073	230,453
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	4,534	4,706
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	2,826	1,604
Segment Assets	103,985		76,238
Energy Marketing [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	56,166	73,159
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	206	255
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	84,541	82,201
Segment Assets	7,146,181		6,733,445
Total Reportable Segments [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	522,795	548,105
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	50,629	40,050
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(6)	675
Segment Assets	76,960		86,460
All Other [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	884	1,700
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	205	(624)
Segment Assets	(78,047)		(80,308)
Corporate And Intersegment Eliminations [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	230	267
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (50,629)	$ (40,050)