Derivative Financial Instruments Derivative Financial Instruments - Oil and Gas Commodity Contracts (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Derivative [Line Items]
Document Period End Date		Jun. 30, 2013
Percentage of production volume covered by derivative financial instruments	76.80%	69.70%
Swap [Member]
Derivative [Line Items]
June 30, 2013	$ 3.5	$ 3.5
Swap [Member] | Natural Gas Commodity Contract [Member]
Derivative [Line Items]
Natural Gas, Volume	21,158,000	21,158,000
June 30, 2013	3.2	3.2
Swap [Member] | Natural Gas Commodity Contract [Member] | Remainder of 2013 [Member]
Derivative [Line Items]
Natural Gas, Volume	10,281,000	10,281,000
Weighted average strike price per Mmbtu/Bbl	3.72	3.72
June 30, 2013	0.8	0.8
Swap [Member] | Natural Gas Commodity Contract [Member] | 2014 [Member]
Derivative [Line Items]
Natural Gas, Volume	10,877,000	10,877,000
Weighted average strike price per Mmbtu/Bbl	4.14	4.14
June 30, 2013	2.4	2.4
Swap [Member] | Oil Commodity Contract [Member]
Derivative [Line Items]
June 30, 2013	0.3	0.3
Derivative, Commodity Contract, Oil Volume	478,000	478,000
Swap [Member] | Oil Commodity Contract [Member] | Remainder of 2013 [Member]
Derivative [Line Items]
Weighted average strike price per Mmbtu/Bbl	94.05	94.05
June 30, 2013	(0.2)	(0.2)
Derivative, Commodity Contract, Oil Volume	206,000	206,000
Swap [Member] | Oil Commodity Contract [Member] | 2014 [Member]
Derivative [Line Items]
Weighted average strike price per Mmbtu/Bbl	91.87	91.87
June 30, 2013	$ 0.5	$ 0.5
Derivative, Commodity Contract, Oil Volume	272,000	272,000