Supplementary Information for Oil and Gas Producing Activities - Proved Developed and Undeveloped Oil and Gas Reserve Quantities (Details) Bcf in Thousands		12 Months Ended
		Sep. 30, 2023 MBbls MMcf Bcf	Sep. 30, 2022 MBbls MMcf Bcf	Sep. 30, 2021 MBbls Bcf MMcf	Sep. 30, 2020 MMcf MBbls
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		985,000,000	858,000,000	636,000,000
Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		4,170,662	3,723,433	3,325,085
Extensions and Discoveries		670,438	837,510	689,395
Revisions of Previous Estimates		32,379	2,953	22,973
Production		(372,271)	(342,911)	(314,020)
Sale of Minerals in Place			(50,323)
Purchases of Minerals in Place		33,876
Proved Developed and Undeveloped Reserves, End of Period		4,535,084	4,170,662	3,723,433
Proved developed reserves volume		3,550,034	3,312,568	3,091,463	2,773,823
Proved undeveloped reserve volume		985,050	858,094	631,970	551,262
Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		250	21,537	22,100
Extensions and Discoveries | MBbls			296	1,041
Revisions of Previous Estimates | MBbls		(4)	787	631
Production		(30)	(1,604)	(2,235)
Sale of Minerals in Place | MBbls			(20,766)
Proved Developed and Undeveloped Reserves, End of Period | MBbls		216	250	21,537
Proved developed reserves volume | MBbls		216	250	20,941	22,100
Proved undeveloped reserve volume | MBbls		0	0	596	0
Appalachian Region | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		4,170,662	3,693,148	3,296,113
Extensions and Discoveries	[1]	670,438	837,510	689,395
Revisions of Previous Estimates		32,379	2,882	19,940
Production	[2]	(372,271)	(341,700)	(312,300)
Sale of Minerals in Place			(21,178)
Purchases of Minerals in Place		33,876
Proved Developed and Undeveloped Reserves, End of Period		4,535,084	4,170,662	3,693,148
Proved developed reserves volume		3,550,034	3,312,568	3,061,178	2,744,851
Proved undeveloped reserve volume		985,050	858,094	631,970	551,262
Appalachian Region | Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		250	11	12
Extensions and Discoveries | MBbls			0	0
Revisions of Previous Estimates | MBbls		(4)	255	1
Production		(30)	(16)	(2)
Sale of Minerals in Place | MBbls			0
Proved Developed and Undeveloped Reserves, End of Period | MBbls		216	250	11
Proved developed reserves volume | MBbls		216	250	11	12
Proved undeveloped reserve volume | MBbls		0	0	0	0
West Coast Region
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf			0	5,000,000
West Coast Region | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		0	30,285	28,972
Extensions and Discoveries		0	0	0
Revisions of Previous Estimates		0	71	3,033
Production		0	(1,211)	(1,720)
Sale of Minerals in Place			(29,145)
Purchases of Minerals in Place		0
Proved Developed and Undeveloped Reserves, End of Period		0	0	30,285
Proved developed reserves volume		0	0	30,285	28,972
Proved undeveloped reserve volume		0	0	0	0
West Coast Region | Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		0	21,526	22,088
Extensions and Discoveries | MBbls			296	1,041
Revisions of Previous Estimates | MBbls		0	532	630
Production		0	(1,588)	(2,233)
Sale of Minerals in Place | MBbls			(20,766)
Proved Developed and Undeveloped Reserves, End of Period | MBbls		0	0	21,526
Proved developed reserves volume | MBbls		0	0	20,930	22,088
Proved undeveloped reserve volume | MBbls		0	0	596	0
Marcellus Shale Fields
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		112,000,000	355,000,000	220,000,000
Marcellus Shale Fields | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		163	301	180
Production		(190,290)	(209,463)	(218,016)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%
Utica Shale
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		873,000,000	503,000,000	411,000,000
Utica Shale | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		507	537	497
Production		(180,750)	(130,240)	(93,253)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%

[1] Extensions and discoveries include 180 Bcf (during 2021), 301 Bcf (during 2022) and 163 Bcf (during 2023), of Marcellus Shale gas (which exceed 15% of total reserves) in the Appalachian region. Extensions and discoveries include 497 Bcf (during 2021), 537 Bcf (during 2022) and 507 Bcf (during 2023), of Utica Shale gas (which exceed 15% of total reserves) in the Appalachian region.

[2] Production includes 218,016 MMcf (during 2021), 209,463 MMcf (during 2022) and 190,290 MMcf (during 2023), from Marcellus Shale fields. Production includes 93,253 MMcf (during 2021), 130,240 MMcf (during 2022) and 180,750 MMcf (during 2023), from Utica Shale fields.