Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 323,019	$ 357,200	$ 1,258,301	$ 1,399,991
Segment Profit: Net Income (Loss)	41,250	63,753	21,773	257,009
Segment Assets	7,118,985		7,118,985		$ 6,462,157
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	323,019	357,200	1,258,301	1,399,991
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	131,228	158,875	452,728	467,853
Segment Profit: Net Income (Loss)	(6,434)	26,512	(157,733)	86,599
Segment Assets	1,886,791		1,886,791		1,972,776
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	131,228	158,875	452,728	467,853
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	77,813	68,967	229,278	218,375
Segment Profit: Net Income (Loss)	22,623	15,792	62,815	58,643
Segment Assets	2,184,289		2,184,289		1,893,514
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	51,020	46,024	151,908	148,663
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	26,793	22,943	77,370	69,712
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	33,299	32,875	103,355	91,933
Segment Profit: Net Income (Loss)	15,239	14,638	51,081	41,511
Segment Assets	706,760		706,760		547,995
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	2
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	33,299	32,875	103,355	91,931
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	127,037	132,921	578,355	658,608
Segment Profit: Net Income (Loss)	6,254	7,362	64,335	68,600
Segment Assets	2,048,181		2,048,181		1,991,338
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	124,390	129,977	569,856	648,624
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	2,647	2,944	8,499	9,984
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	37,682	64,304	20,498	255,353
Segment Assets	6,826,021		6,826,021		6,405,623
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	306,638	334,876	1,174,492	1,265,142
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	62,739	58,762	189,224	171,627
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	16,627	22,870	84,043	135,661
Segment Profit: Net Income (Loss)	(9)	(1,444)	1,532	(946)
Segment Assets	123,666		123,666		122,241
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	16,286	22,189	83,445	134,605
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	341	681	598	1,056
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(62,985)	(59,308)	(189,458)	(172,439)
Segment Profit: Net Income (Loss)	3,577	893	(257)	2,602
Segment Assets	169,298		169,298		$ (65,707)
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	95	135	364	244
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (63,080)	$ (59,443)	$ (189,822)	$ (172,683)