Supplementary Information On Natural Gas, Oil And NGL Reserves (Narrative) (Details)	12 Months Ended
	Sep. 30, 2020 Mcfe $ / bbl $ / Mcf	Sep. 30, 2020 Bcfe Mcfe $ / bbl $ / Mcf	Sep. 30, 2020 Mcfe $ / bbl $ / Mcf	Sep. 30, 2019 Bcfe $ / bbl	Sep. 30, 2018 Bcfe $ / bbl $ / Mcf	Sep. 30, 2019 Bcfe	Sep. 30, 2019 $ / Mcf	Sep. 30, 2019 Mcfe
Supplementary Oil And Gas Disclosures [Line Items]
Negative pricing revisions		35.8
Negative revisions, developed		20.4
Negative revisions, undeveloped		15.4
Negative revisions		10.1
Negative revisions, undeveloped		1.4
Proved developed reserve extensions, discoveries and other additions		4.1
Proved developed reserve		1.7
Proved undeveloped reserve		2.4
Production of oil and natural gas properties		8.6		10.4	12.3
Proved undeveloped Reserves	3,060,656	3,060,656	3,060,656			17.0		17,018,905
Net PUD reserves decreased		14.0
Proved undeveloped reserves transferred to proved developed		0.4	399,894
Percentage transferred to proved developed	2.00%
Remaining revisions of proved undeveloped reserves		13.6
Revisions percentage of proved undeveloped reserves	80.00%
Proved undeveloped reserves revisions of sales and performance		1.8
Proved undeveloped reserves revisions of purchases and extensions		3.6
Proved undeveloped reserves, additions		2.4
COVID-19 [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Negative revisions, undeveloped		15.4
STACK and Arkoma Stack [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Negative revisions, developed		8.7
Eddy County, New Mexico [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Divestiture of permain basin		0.7
Proved developed sale		0.2
Proved undeveloped sale		0.5
Additional proved undeveloped sale		0.5
Oklahoma [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Additional proved undeveloped acquisition		1.3
Oil [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	40.18	40.18	40.18	54.40	62.86
NGL [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	9.95	9.95	9.95	19.30	26.13
Natural Gas [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / Mcf	1.62	1.62	1.62		2.56		2.48
Oil, NGL And Natural Gas [Member] | Woodford, Mississippian, Oklahoma and North Dakota [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Acquisition		2.4
Proved developed acquisition		1.1
Proved undeveloped acquisition		1.3