Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 357,200	$ 342,912	$ 1,399,991	$ 1,303,473
Segment Profit: Net Income (Loss)	63,753	63,025	257,009	353,527
Segment Assets	6,336,247		6,336,247		$ 6,036,486
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	357,200	342,912	1,399,991	1,303,473
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	158,875		467,853
Segment Profit: Net Income (Loss)	26,512	27,817	86,599	161,052
Segment Assets	1,847,706		1,847,706		1,568,563
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	158,875	135,828	467,853	421,381
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]
Revenue	68,967		218,375
Segment Profit: Net Income (Loss)	15,792	20,723	58,643	81,909
Segment Assets	1,894,824		1,894,824		1,848,180
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	46,024	51,363	148,663	158,387
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	22,943	22,496	69,712	67,524
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	32,875		91,933
Segment Profit: Net Income (Loss)	14,638	11,566	41,511	68,736
Segment Assets	555,185		555,185		533,608
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	(31)	2	41
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	32,875	27,908	91,931	79,404
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	132,921		658,608
Segment Profit: Net Income (Loss)	7,362	3,930	68,600	58,283
Segment Assets	1,967,123		1,967,123		1,921,971
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	129,977	128,628	648,624	599,495
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	2,944	3,519	9,984	11,401
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	22,016		133,491
Segment Profit: Net Income (Loss)	(1,441)	(190)	(1,198)	1,434
Segment Assets	45,736		45,736		50,971
Energy Marketing [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	21,335	25,460	132,435	119,739
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	681	512	1,056	589
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	62,863	63,846	254,155	371,414
Segment Assets	6,310,574		6,310,574		5,923,293
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	356,211	341,248	1,397,577	1,299,043
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	59,443	54,435	172,683	158,918
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	854		2,170
Segment Profit: Net Income (Loss)	(3)	297	252	(214)
Segment Assets	78,528		78,528		78,109
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	854	1,496	2,170	3,824
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]
Revenue	(59,308)		(172,439)
Segment Profit: Net Income (Loss)	893	(1,118)	2,602	(17,673)
Segment Assets	(52,855)		(52,855)		$ 35,084
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	135	168	244	606
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (59,443)	$ (54,435)	$ (172,683)	$ (158,918)