Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 198,654	$ 88,908
Segment Assets	5,791,932		$ 6,103,320
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	419,655	422,500
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	106,698	35,080
Segment Assets	1,420,790		1,407,152
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	139,141	160,932
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	38,462	19,368
Segment Assets	1,793,848		1,929,788
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	53,310	53,000
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	21,985	22,155
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	45,400	10,981
Segment Assets	589,793		580,051
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	170	26
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	23,665	27,840
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	20,993	21,175
Segment Assets	1,988,758		2,013,123
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	187,089	170,971
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	2,182	1,826
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	1,046	1,782
Segment Assets	72,466		60,937
Energy Marketing [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	38,636	36,809
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	126	19
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	212,599	88,386
Segment Assets	5,865,655		5,991,051
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	418,346	421,738
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	47,958	51,840
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(719)	(179)
Segment Assets	77,214		76,861
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	1,096	554
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)	(13,226)	701
Segment Assets	(150,937)		$ 35,408
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	213	208
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (47,958)	$ (51,840)