Supplementary Information On Oil, Ngl And Natural Gas Reserves (Summary of Net Quantities of Proved, Developed and Undeveloped Oil and Natural Gas Reserves) (Details)	12 Months Ended
	Sep. 30, 2013 bbl		Sep. 30, 2012 bbl		Sep. 30, 2011 bbl
Oil [Member]
Reserve Quantities [Line Items]
Proved Oil and Natural Gas Reserves, Beginning Balance	1,072,319		843,738		925,009
Revisions of previous estimates	(90,968)		8,627		(59,360)
Extensions and discoveries and other additions	896,036		373,097		82,230
Production	(234,084)		(153,143)		(104,141)
Proved Oil and Natural Gas Reserves, Ending Balance	1,643,303		1,072,319		843,738
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Oil and Natural Gas Reserves, Beginning Balance	788,742	[1],[2]	791,648	[1],[2]
Revisions of previous estimates	141,081	[1],[2]	(76,794)	[1],[2]	791,648	[1],[2]
Extensions and discoveries and other additions	798,200	[1],[2]	172,602	[1],[2]
Production	(111,897)	[1],[2]	(98,714)	[1],[2]
Proved Oil and Natural Gas Reserves, Ending Balance	1,616,126	[1],[2]	788,742	[1],[2]	791,648	[1],[2]
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Oil and Natural Gas Reserves, Beginning Balance	113,514,056		101,837,984		98,170,455
Revisions of previous estimates	(2,697,853)		(27,389,752)		769,676
Divestitures					3,189,520
Acquisitions	1,660,649		19,075,529
Extensions and discoveries and other additions	30,698,644		29,062,593		8,005,990
Production	(10,886,329)		(9,072,298)		(8,297,657)
Proved Oil and Natural Gas Reserves, Ending Balance	132,289,167		113,514,056		101,837,984

[1] 2011 was the first year the Company had sufficient volumes of NGL to warrant reserve volumes disclosure.

[2] 2011 was the first year the Company had sufficient volumes of NGL to warrant reserve volumes disclosure. These NGL are associated with the rapid increase in drilling activity in western and southern Oklahoma and the Texas Panhandle, which includes many plays (horizontal Granite Wash, Hogshooter Wash, Cleveland, Marmaton, Anadarko Basin Woodford Shale and Ardmore Basin Woodford Shale) producing significant volumes of NGL.