Supplementary Information On Oil, NGL And Natural Gas Reserves (Narrative) (Details)	12 Months Ended
	Sep. 30, 2019 Bcfe Mcfe $ / bbl $ / Mcf	Sep. 30, 2018 Bcfe Mcfe $ / bbl $ / Mcf	Sep. 30, 2017 Bcfe $ / bbl $ / Mcf
Supplementary Oil And Gas Disclosures [Line Items]
Negative pricing revisions	4,400,000
Negative revisions, developed	4,300,000
Negative revisions, undeveloped	100,000
Negative revisions	56,200,000
Proved developed reserve extensions, discoveries and other additions	2,100,000
Proved undeveloped reserves, additions	4,700,000
Production of oil and natural gas properties | Bcfe	10.4	12.3	11.1
Proved undeveloped Reserves	17,018,905	63,899,996
Proved undeveloped reserves transferred to proved developed	1,763,402
Percentage transferred to proved developed	3.00%
Revisions of proved undeveloped reserves	48,404,716
Revisions percentage of proved undeveloped reserves	76.00%
Arkoma Stack [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Negative revisions, developed	8,000,000
Eagle Ford [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Negative revisions, undeveloped	48,200,000
Bakken, North Dakota [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Additional proved undeveloped acquisition	300,000
Texas and New Mexico [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Divestiture of permain basin	3,800,000
Proved developed sale	2,200,000
Proved undeveloped sale	1,600,000
Additional proved undeveloped sale	1,600,000
Oil [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	54.40	62.86	46.31
NGL [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	19.30	26.13	17.55
Natural Gas [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / Mcf	2.48	2.56	2.81
Oil, NGL And Natural Gas [Member] | Bakken, North Dakota [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Acquisition	800,000
Proved developed acquisition	500,000
Proved undeveloped acquisition	300,000