Business Segment Information (Segment Information By Segment) (Details) (USD $)	3 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 432,423,000	$ 450,948,000
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	60,699,000	58,543,000
Utility [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	208,810,000	242,842,000
Intersegment Revenues	4,389,000	4,570,000
Segment Profit: Net Income (Loss)	19,353,000	22,990,000
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	35,225,000	33,513,000
Intersegment Revenues	21,064,000	19,882,000
Segment Profit: Net Income (Loss)	9,959,000	8,578,000
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	216,600,000
Revenue from External Customers	135,974,000	120,168,000
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	30,315,000	27,373,000
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	51,222,000	53,652,000
Intersegment Revenues	287,000	0
Segment Profit: Net Income (Loss)	429,000	932,000
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	431,231,000	450,175,000
Intersegment Revenues	25,740,000	24,452,000
Segment Profit: Net Income (Loss)	60,056,000	59,873,000
All Other [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	937,000	549,000
Intersegment Revenues	3,362,000	1,678,000
Segment Profit: Net Income (Loss)	1,404,000	(574,000)
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	204,600,000
Revenue from External Customers	255,000	224,000
Intersegment Revenues	(29,102,000)	(26,130,000)
Segment Profit: Net Income (Loss)	$ (761,000)	$ (756,000)