Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 549,482	$ 525,361
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	44,986	133,020
Segment Assets:	8,301,448		$ 8,319,770
Total Reportable Segments | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	549,482	525,361
Intersegment Revenues	95,630	87,666
Segment Profit: Net Income (Loss)	45,321	131,914
Segment Assets:	8,502,635		8,476,875
Exploration and Production | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	248,860	254,019
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	(46,777)	52,483
Segment Assets:	2,533,521		2,644,820
Pipeline and Storage | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	68,750	64,826
Intersegment Revenues	37,862	29,587
Segment Profit: Net Income (Loss)	32,454	24,055
Segment Assets:	2,475,767		2,446,243
Gathering | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	3,448	4,596
Intersegment Revenues	57,683	57,992
Segment Profit: Net Income (Loss)	27,145	28,825
Segment Assets:	1,039,149		987,103
Utility | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	228,424	201,920
Intersegment Revenues	85	87
Segment Profit: Net Income (Loss)	32,499	26,551
Segment Assets:	2,454,198		2,398,709
All Other | All Other
Segment Reporting Information [Line Items]
Revenue from External Customers	0	0
Intersegment Revenues	0	0
Segment Profit: Net Income (Loss)	(193)	(121)
Segment Assets:	7,931		6,227
Corporate and Intersegment Eliminations | Corporate
Segment Reporting Information [Line Items]
Revenue from External Customers	0	0
Corporate and Intersegment Eliminations | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues	(95,630)	(87,666)
Segment Profit: Net Income (Loss)	(142)	$ 1,227
Segment Assets:	$ (209,118)		$ (163,332)