Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 342,912	$ 348,368	$ 1,303,473	$ 1,292,944
Segment Profit: Net Income (Loss)	63,025	59,714	353,527	237,906
Segment Assets	5,974,103		5,974,103		$ 6,103,320
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	342,912	348,368	1,303,473	1,292,944
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	27,817	30,123	161,052	98,972
Segment Assets	1,591,783		1,591,783		1,407,152
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	135,828	151,161	421,381	471,646
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	20,723	16,031	81,909	54,656
Segment Assets	1,763,620		1,763,620		1,929,788
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	51,363	50,049	158,387	156,212
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	22,496	21,643	67,524	66,389
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	11,566	10,107	68,736	31,373
Segment Assets	534,086		534,086		580,051
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	(31)	34	41	86
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	27,908	26,853	79,404	82,629
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	3,930	4,348	58,283	51,103
Segment Assets	1,904,189		1,904,189		2,013,123
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	128,628	121,900	599,495	550,819
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	3,519	3,391	11,401	11,314
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(190)	(564)	1,434	2,122
Segment Assets	51,778		51,778		60,937
Energy Marketing [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	25,460	24,460	119,739	112,210
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	512	565	589	600
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	63,846	60,045	371,414	238,226
Segment Assets	5,845,456		5,845,456		5,991,051
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	341,248	347,604	1,299,043	1,290,973
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	54,435	52,452	158,918	160,932
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	297	(98)	(214)	(498)
Segment Assets	77,879		77,879		76,861
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	1,496	538	3,824	1,311
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(1,118)	(233)	(17,673)	178
Segment Assets	50,768		50,768		$ 35,408
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	168	226	606	660
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (54,435)	$ (52,452)	$ (158,918)	$ (160,932)