Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenue	$ 502,624	$ 394,397	$ 1,750,900	$ 1,386,671
Segment Profit: Net Income (Loss)	108,158	86,475	407,879	276,685
Segment Assets	8,112,086		8,112,086		$ 7,464,825
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	502,624	394,397	1,750,900	1,386,671
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	252,638	209,535	758,428	621,116
Segment Profit: Net Income (Loss)	56,497	39,015	189,987	46,213
Segment Assets	2,716,219		2,716,219		2,286,058
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	252,638	209,535	758,428	621,116
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	95,548	84,063	279,295	258,532
Segment Profit: Net Income (Loss)	26,599	21,948	77,236	71,060
Segment Assets	2,371,621		2,371,621		2,296,030
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	67,236	57,258	196,579	175,881
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	28,312	26,805	82,716	82,651
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	55,931	48,656	160,759	145,927
Segment Profit: Net Income (Loss)	24,658	20,427	69,887	61,677
Segment Assets	870,204		870,204		837,729
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	2,862	588	10,063	1,610
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	53,069	48,068	150,696	144,317
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	179,948	127,008	785,909	586,889
Segment Profit: Net Income (Loss)	4,622	4,841	79,800	59,922
Segment Assets	2,247,229		2,247,229		2,148,267
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	179,888	126,934	785,664	586,618
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	60	74	245	271
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	112,376	86,231	416,910	238,872
Segment Assets	8,205,273		8,205,273		7,568,084
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	502,624	394,315	1,750,734	1,385,225
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	81,441	74,947	233,657	227,239
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	0	1	6	1,196
Segment Profit: Net Income (Loss)	0	1,039	(7)	37,617
Segment Assets	235		235		4,146
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	(1)	0	1,174
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	2	6	22
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(81,441)	(74,866)	(233,497)	(226,989)
Segment Profit: Net Income (Loss)	(4,218)	(795)	(9,024)	196
Segment Assets	(93,422)		(93,422)		$ (107,405)
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	83	166	272
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (81,441)	$ (74,949)	$ (233,663)	$ (227,261)