Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2024
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 531,830	$ 417,442	$ 1,811,262	$ 1,572,742
Intersegment Revenues	0	0	0	0
Segment Profit: Net Income (Loss)	149,818	(54,158)	411,162	245,134
Segment Assets:	8,446,160		8,446,160		$ 8,319,770
Total Reportable Segments \| Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	531,830	417,442	1,811,262	1,572,742
Intersegment Revenues	103,028	93,946	298,962	278,804
Segment Profit: Net Income (Loss)	150,521	(53,800)	415,264	244,361
Segment Assets:	8,528,699		8,528,699		8,476,875
Exploration and Production \| Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	303,883	220,905	864,701	739,537
Intersegment Revenues	0	0	0	0
Segment Profit: Net Income (Loss)	86,671	(112,028)	137,722	2,521
Segment Assets:	2,574,771		2,574,771		2,644,820
Pipeline and Storage \| Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	67,982	68,035	207,916	204,071
Intersegment Revenues	37,597	37,384	113,849	103,781
Segment Profit: Net Income (Loss)	28,857	30,690	93,019	85,482
Segment Assets:	2,421,610		2,421,610		2,446,243
Gathering \| Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	2,519	3,644	9,200	12,157
Intersegment Revenues	65,354	56,476	184,834	174,544
Segment Profit: Net Income (Loss)	29,996	24,979	83,483	82,510
Segment Assets:	1,024,345		1,024,345		987,103
Utility \| Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	157,446	124,858	729,445	616,977
Intersegment Revenues	77	86	279	479
Segment Profit: Net Income (Loss)	4,997	2,559	101,040	73,848
Segment Assets:	2,507,973		2,507,973		2,398,709
All Other \| All Other
Segment Reporting Information [Line Items]
Revenue from External Customers	0	0	0	0
Intersegment Revenues	0	0	0	0
Segment Profit: Net Income (Loss)	(209)	(124)	(674)	(341)
Segment Assets:	8,216		8,216		6,227
Corporate and Intersegment Eliminations \| Corporate
Segment Reporting Information [Line Items]
Revenue from External Customers	0	0	0	0
Corporate and Intersegment Eliminations \| Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues	(103,028)	(93,946)	(298,962)	(278,804)
Segment Profit: Net Income (Loss)	(494)	$ (234)	(3,428)	$ 1,114
Segment Assets:	$ (90,755)		$ (90,755)		$ (163,332)