Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenue	$ 701,720	$ 551,115	$ 1,248,277	$ 992,275
Segment Profit: Net Income (Loss)	167,328	112,436	299,720	190,210
Segment Assets	7,805,023		7,805,023		$ 7,464,825
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	701,720	551,115	1,248,277	992,275
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	261,593	220,187	505,791	411,582
Segment Profit: Net Income (Loss)	71,121	36,822	133,490	7,199
Segment Assets	2,535,426		2,535,426		2,286,058
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	261,593	220,187	505,791	411,582
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	95,397	86,704	183,747	174,469
Segment Profit: Net Income (Loss)	25,470	24,928	50,637	49,112
Segment Assets	2,330,802		2,330,802		2,296,030
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	67,795	59,314	129,342	118,623
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	27,602	27,390	54,405	55,846
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	52,604	50,262	104,829	97,270
Segment Profit: Net Income (Loss)	22,092	20,700	45,229	41,250
Segment Assets	845,379		845,379		837,729
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	3,157	671	7,202	1,021
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	49,447	49,591	97,627	96,249
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	369,202	270,881	605,960	459,881
Segment Profit: Net Income (Loss)	53,048	32,044	75,178	55,081
Segment Assets	2,247,733		2,247,733		2,148,267
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	369,092	270,784	605,776	459,684
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	110	97	184	197
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	171,731	114,494	304,534	152,642
Segment Assets	7,959,340		7,959,340		7,568,084
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	701,637	550,956	1,248,111	990,910
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	77,159	77,078	152,216	152,292
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	0	65	6	1,195
Segment Profit: Net Income (Loss)	0	(983)	(7)	36,577
Segment Assets	235		235		4,146
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	64	0	1,175
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	1	6	20
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(77,076)	(76,984)	(152,056)	(152,122)
Segment Profit: Net Income (Loss)	(4,403)	(1,075)	(4,807)	991
Segment Assets	(154,552)		(154,552)		$ (107,405)
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	83	95	166	190
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (77,159)	$ (77,079)	$ (152,222)	$ (152,312)