Business Segment Information (Segment Information By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 452,854	$ 432,423
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	67,944	60,699
Utility [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	208,563	208,810
Intersegment Revenues	4,311	4,389
Segment Profit: Net Income (Loss)	22,878	19,353
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	43,459	35,225
Intersegment Revenues	22,797	21,064
Segment Profit: Net Income (Loss)	16,933	9,959
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	155,450	135,974
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	26,680	30,315
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	44,166	51,222
Intersegment Revenues	426	287
Segment Profit: Net Income (Loss)	495	429
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	451,638	431,231
Intersegment Revenues	27,534	25,740
Segment Profit: Net Income (Loss)	66,986	60,056
All Other [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	1,015	937
Intersegment Revenues	5,480	3,362
Segment Profit: Net Income (Loss)	1,885	1,404
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	201	255
Intersegment Revenues	(33,014)	(29,102)
Segment Profit: Net Income (Loss)	$ (927)	$ (761)