Supplemental Information Relating to Oil and Natural Gas Producing Activities (Unaudited) - Schedule of Capitalized Costs of Unproved Properties Excluded from Amortization (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Compass
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	$ 18.9
Acquisition Costs, Period Cost	0	18.9
Capitalized interest	1.3
Capitalized Interest Excluded from Amortization, Period Costs	0.7	0.6
Total	20.2
Capitalized Costs of Unproved Properties Excluded from Amortization, Period Cost	$ 0.7	$ 19.5
Minimum
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Anticipated Timing of Inclusion of Costs in Amortization Calculation	P1Y
Maximum
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Anticipated Timing of Inclusion of Costs in Amortization Calculation	P4Y