Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenue from External Customers	$ 629,939	$ 717,261	$ 1,155,301
Intersegment Revenues	0	0	0
Segment Profit: Net Income (Loss)	166,272	140,880	299,292	$ 310,570
Segment Assets:	8,677,025		8,677,025		$ 8,280,260
Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers				1,376,119
Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues				0
Total Reportable Segments
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)			298,160	310,118
Total Reportable Segments | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	629,939	717,261	1,155,301	1,376,119
Intersegment Revenues	97,192	86,491		170,355
Segment Profit: Net Income (Loss)	166,247	140,894
Segment Assets:	8,853,383		8,853,383		8,402,098
Total Reportable Segments | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues			184,858
Exploration and Production
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)			114,548	152,174
Exploration and Production | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	264,614	244,552	518,633	521,525
Intersegment Revenues	0	0		0
Segment Profit: Net Income (Loss)	62,065	60,982
Segment Assets:	3,049,670		3,049,670		2,814,218
Exploration and Production | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues			0
Pipeline and Storage
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)			54,792	53,335
Pipeline and Storage | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	71,210	64,223	136,036	131,844
Intersegment Revenues	36,810	30,880		60,915
Segment Profit: Net Income (Loss)	30,737	23,858
Segment Assets:	2,472,011		2,472,011		2,427,214
Pipeline and Storage | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues			66,397
Gathering
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)			57,531	49,072
Gathering | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	3,917	1,728	8,513	4,374
Intersegment Revenues	60,076	55,253		109,020
Segment Profit: Net Income (Loss)	28,706	24,334
Segment Assets:	971,741		971,741		912,923
Gathering | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues			118,068
Utility
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)			71,289	55,537
Utility | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenue from External Customers	290,198	406,758	492,119	718,376
Intersegment Revenues	306	358		420
Segment Profit: Net Income (Loss)	44,739	31,720
Segment Assets:	2,359,961		2,359,961		2,247,743
Utility | Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues			393
All Other
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)				(350)
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)	(96)	(69)	(217)
Segment Assets:	4,823		4,823		4,795
Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)				802
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	(97,192)	(86,491)	(184,858)	$ (170,355)
Segment Profit: Net Income (Loss)	121	$ 55	1,349
Segment Assets:	$ (181,181)		$ (181,181)		$ (126,633)