Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 490,247	$ 419,655
Segment Profit: Net Income (Loss)	102,660	198,654
Segment Assets	6,186,928		$ 6,036,486
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	490,247	419,655
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	162,876
Segment Profit: Net Income (Loss)	38,214	106,698
Segment Assets	1,691,903		1,568,563
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	162,876	139,141
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue	77,069
Segment Profit: Net Income (Loss)	25,102	38,462
Segment Assets	1,860,220		1,848,180
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	54,218	53,310
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	22,851	21,985
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	29,690
Segment Profit: Net Income (Loss)	14,183	45,400
Segment Assets	538,551		533,608
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	170
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	29,690	23,665
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	222,657
Segment Profit: Net Income (Loss)	25,649	20,993
Segment Assets	1,995,606		1,921,971
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	220,012	187,089
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	2,645	2,182
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	52,412
Segment Profit: Net Income (Loss)	(302)	1,046
Segment Assets	64,790		50,971
Energy Marketing [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	52,080	38,636
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	332	126
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	102,846	212,599
Segment Assets	6,151,070		5,923,293
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	489,186	418,346
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	55,518	47,958
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	1,007
Segment Profit: Net Income (Loss)	384	(719)
Segment Assets	78,560		78,109
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	1,007	1,096
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(55,464)
Segment Profit: Net Income (Loss)	(570)	(13,226)
Segment Assets	(42,702)		$ 35,084
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	54	213
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (55,518)	$ (47,958)