Supplementary Information on Oil, Ngl and Natural Gas Reserves (Unaudited) (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Reserve Quantities [Line Items]
Proved Undeveloped Reserves	50,885,055	44,575,844
Percentage of PUD reserves total	8.00%
Number of PUD location	589
Supplementary information on oil and natural gas reserves (Textual) [Abstract]
Positive performance revisions	3,613,707
Proved Developed Reserves (Energy)	1,644,157
Proved undeveloped revisions	1,969,550
Negative proved developed revisions	7,073,763
Negative gas pricing revisions	31,412,464
Negative proved undeveloped revisions	24,338,701
Acquisition of mineral acreage with proved reserves	$ 17.4	$ 3.9
Percentage of annual discount factor	10.00%
Oil [Member]
Reserve Quantities [Line Items]
Prices used to calculate reserves and future cash flows from reserves from NGL	89.41	90.28	69.23
Natural Gas [Member]
Reserve Quantities [Line Items]
Prices used to calculate reserves and future cash flows from reserves for natural gas	2.51	3.81	4.33
Proved undeveloped reserves transferred to proved developed	5,400,000
Percentage transferred to proved developed	12.00%
Additional undeveloped reserves removed	24,300,000
Percentage of additional undeveloped reserves removed	55.00%
Total proved undeveloped reserves moved out	29,700,000
Percentage of proved undeveloped reserves moved out	67.00%
Period for converting PUD to PDP	5 years
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Prices used to calculate reserves and future cash flows from reserves from NGL	35.70	38.91
2008 [Member]
Reserve Quantities [Line Items]
Percentage of PUD reserves	1.00%
Number of PUD location	1
2009 [Member]
Reserve Quantities [Line Items]
Percentage of PUD reserves	11.00%
Number of PUD location	45
2008 and 2009 [Member]
Reserve Quantities [Line Items]
Number of PUD location	46