Supplemental Information on Oil and Natural Gas Operations (Unaudited) - Oil, Natural Gas and NGL Quantities (Details)	12 Months Ended
	Sep. 30, 2021 MBoe MBbls MMcf	Sep. 30, 2020 MBoe MMcf MBbls	Sep. 30, 2019 MBoe MBbls MMcf
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Beginning balance | MBoe	56,787	54,803
Extensions and discoveries | MBoe	13,759	3,412
Revisions | MBoe	4,772	1,163
Production | MBoe	(3,155)	(2,591)
Ending balance | MBoe	72,163	56,787
Proved Developed Reserves, Included Above | MBoe	41,516	30,186	29,092
Proved Undeveloped Reserves, Included Above | MBoe	30,647	26,601	25,711
Oil
Proved Developed and Undeveloped Reserves [Roll Forward]
Beginning balance	37,158	37,159
Extensions and discoveries	9,308	2,265
Revisions	2,138	(206)
Production	(2,341)	(2,060)
Ending balance	46,263	37,158
Proved Developed Reserves, Included Above	26,170	19,149	19,198
Proved Undeveloped Reserves, Included Above	20,093	18,009	17,961
Natural Gas
Proved Developed and Undeveloped Reserves [Roll Forward]
Beginning balance | MMcf	53,683	40,991
Extensions and discoveries | MMcf	12,089	3,030
Revisions | MMcf	12,850	11,290
Production | MMcf	(2,603)	(1,628)
Ending balance | MMcf	76,019	53,683
Proved Developed Reserves, Included Above | MMcf	46,173	31,137	23,096
Proved Undeveloped Reserves, Included Above | MMcf	29,846	22,546	17,895
NGLs
Proved Developed and Undeveloped Reserves [Roll Forward]
Beginning balance	10,681	10,812
Extensions and discoveries	2,436	642
Revisions	492	(513)
Production	(380)	(260)
Ending balance	13,229	10,681
Proved Developed Reserves, Included Above	7,650	5,847	6,045
Proved Undeveloped Reserves, Included Above	5,579	4,834	4,767