Business Segment Information (Financial Segment Information By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 82,252	$ 67,944
Segment Assets	6,264,984		6,218,347
Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	550,072	452,854
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	24,215	22,878
Segment Assets	1,911,689		1,870,587
Utility [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	230,453	208,563
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	4,706	4,311
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	19,138	16,933
Segment Assets	1,244,551		1,246,027
Pipeline And Storage [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	51,212	43,459
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	20,739	22,797
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	31,097	26,680
Segment Assets	2,752,386		2,746,233
Exploration And Production [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	193,046	155,450
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	1,604	495
Segment Assets	93,735		67,267
Energy Marketing [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	73,159	44,166
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	255	426
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	6,147	1,942
Segment Assets	225,191		203,323
Gathering [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	235	202
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	14,350	5,480
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	82,201	68,928
Segment Assets	6,227,552		6,133,437
Total Reportable Segments [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	548,105	451,840
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	40,050	33,014
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	675	(57)
Segment Assets	95,541		95,793
All Other [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	1,700	813
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)	(624)	(927)
Segment Assets	(58,109)		(10,883)
Corporate And Intersegment Eliminations [Member] | Revenue From External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	267	201
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (40,050)	$ (33,014)