Business Segment Information (Financial Segment Information By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2013
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 64,520	$ 58,495	$ 241,983	$ 212,159
Segment Assets	6,588,458		6,588,458		6,218,347
Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	440,144	440,008	1,746,458	1,490,688
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)	32,421	31,734	87,908	86,125
Segment Assets	2,943,692		2,943,692		2,746,233
Exploration And Production [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	201,522	195,213	594,129	518,742
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)	17,934	14,075	58,444	47,803
Segment Assets	1,304,619		1,304,619		1,246,027
Pipeline And Storage [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	48,046	43,055	152,829	132,897
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	20,489	21,708	63,463	68,216
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	8,717	4,407	22,188	9,442
Segment Assets	292,630		292,630		203,323
Gathering [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	343	342	772	868
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	18,740	10,244	48,541	23,622
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	4,826	7,630	64,586	65,024
Segment Assets	1,952,626		1,952,626		1,870,587
Utility [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	143,760	141,257	751,861	653,211
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	3,654	3,305	16,565	14,012
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	602	963	5,971	5,741
Segment Assets	87,367		87,367		67,267
Energy Marketing [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	45,737	59,128	243,335	182,282
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	678	446	938	1,080
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	64,500	58,809	239,097	214,135
Segment Assets	6,580,934		6,580,934		6,133,437
Total Reportable Segments [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	439,408	438,995	1,742,926	1,488,000
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	43,561	35,703	129,507	106,930
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	24	92	978	7
Segment Assets	96,192		96,192		95,793
All Other [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	497	779	2,795	2,030
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)	(4)	(406)	1,908	(1,983)
Segment Assets	(88,668)		(88,668)		(10,883)
Corporate And Intersegment Eliminations [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	239	234	737	658
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (43,561)	$ (35,703)	$ (129,507)	$ (106,930)