Business Segment Information (Segment Information By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 328,861	$ 380,979	$ 1,313,593	$ 1,492,808
Intersegment Revenues	0	0	0	0
Segment Profit: Net Income (Loss)	43,184	46,891	171,275	221,045
Utility [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	117,240	146,215	622,836	750,802
Intersegment Revenues	2,703	3,475	12,643	14,680
Segment Profit: Net Income (Loss)	5,096	6,328	52,725	62,399
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	36,631	29,933	113,976	103,115
Intersegment Revenues	22,076	20,324	64,434	60,838
Segment Profit: Net Income (Loss)	12,627	4,503	35,428	24,036
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	138,549	130,974	411,449	388,571
Intersegment Revenues	0	0	0	0
Segment Profit: Net Income (Loss)	21,915	32,784	74,422	93,455
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	35,377	71,746	161,822	246,719
Intersegment Revenues	579	156	1,135	156
Segment Profit: Net Income (Loss)	923	1,891	4,662	9,122
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	327,797	378,868	1,310,083	1,489,207
Intersegment Revenues	25,358	23,955	78,212	75,674
Segment Profit: Net Income (Loss)	40,561	45,506	167,237	189,012
All Other [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	824	1,873	2,784	2,895
Intersegment Revenues	4,307	2,810	10,828	7,026
Segment Profit: Net Income (Loss)	2,815	2,713	5,557	34,320
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	240	238	726	706
Intersegment Revenues	(29,665)	(26,765)	(89,040)	(82,700)
Segment Profit: Net Income (Loss)	$ (192)	$ (1,328)	$ (1,519)	$ (2,287)