Derivative Financial Instruments Derivative Financial Instruments - Oil and Gas Commodity Contracts (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2014 Swap [Member] Natural Gas Commodity Contract [Member] MMBTU	Sep. 30, 2013 Swap [Member] Natural Gas Commodity Contract [Member] MMBTU	Mar. 31, 2014 Swap [Member] Natural Gas Commodity Contract [Member] Remainder of 2014 [Member] MMBTU	Mar. 31, 2014 Swap [Member] Oil Commodity Contract [Member] MBbls	Sep. 30, 2013 Swap [Member] Oil Commodity Contract [Member] MBbls	Mar. 31, 2014 Swap [Member] Oil Commodity Contract [Member] Remainder of 2014 [Member] MBbls
Derivative [Line Items]
Derivative, Percentage of Production Volume Covered by Derivative Financial Instruments	69.00%	54.00%	77.00%
Document Period End Date			Mar. 31, 2014
Natural Gas, Volume				12,272,000.0	16,018,000.0	12,272,000.0
Weighted average strike price per Mmbtu/Bbl						4.15			91.87
March 31, 2014				$ (3.8)		$ (3.8)	$ (1.2)		$ (1.2)
Derivative, Commodity Contract, Oil Volume							205,000.0	375.0	205,000.0