Supplementary Information On Oil, NGL And Natural Gas Reserves (Narrative) (Details)	12 Months Ended	24 Months Ended
	Sep. 30, 2018 Mcfe $ / bbl $ / Mcf	Sep. 30, 2018 Mcfe $ / bbl $ / Mcf	Sep. 30, 2017 Mcfe $ / bbl $ / Mcf	Sep. 30, 2016 $ / bbl $ / Mcf
Supplementary Oil And Gas Disclosures [Line Items]
Negative pricing revisions	2,400,000
Negative revisions, developed	1,700,000
Negative revisions, undeveloped	700,000
Negative performance revisions	4,200,000
Proved developed reserve extensions, discoveries and other additions	3,700,000
Proved undeveloped reserves, additions	20,400,000
Proved undeveloped Reserves	63,899,996	63,899,996	56,880,555
Proved undeveloped reserves transferred to proved developed	2,158,716
Percentage transferred to proved developed	4.00%	41.00%
Revisions of proved undeveloped reserves	12,456,931
Revisions percentage of proved undeveloped reserves	22.00%
Proved undeveloped reserves drilled or completed	1,200,000
Anadarko Basin Woodford and Southeastern Oklahoma Woodford [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Positive revisions, developed	7,600,000
Eagle Ford [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Negative revisions, undeveloped	11,800,000
Program development projected period	5 years
Northwestern Oklahoma and Kearny County, Kansas [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Divestiture of marginal properties	2,800,000
Oil [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	62.86	62.86	46.31	36.77
Natural Gas Liquids [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / bbl	26.13	26.13	17.55	12.22
Natural Gas [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Price used to calculate reserves and future cash flows from reserves | $ / Mcf	2.56	2.56	2.81	1.97
Oil, NGL And Natural Gas [Member] | Bakken, North Dakota [Member]
Supplementary Oil And Gas Disclosures [Line Items]
Acquisition	2,600,000
Proved developed acquisition	1,400,000
Proved undeveloped acquisition	1,200,000