Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified		12 Months Ended	9 Months Ended		3 Months Ended
	Sep. 30, 2014	Dec. 31, 2010 Legal Reserve	Sep. 30, 2014 Contract Drilling	Sep. 30, 2014 Maximum Contract Drilling	Sep. 30, 2014 Maximum Firm Transportation	Sep. 30, 2014 Minimum Firm Transportation	Sep. 30, 2014 Gas Gathering And Compression Services	Sep. 30, 2014 Crude Oil Gathering And Transportation Services
Commitments and Contingencies Disclosure [Line Items]
Contract term				11 months	15 years	1 year
Contract termination claims description			early termination provisions that would require us to pay penalties if we terminate the agreements prior to the end of their scheduled terms.
Loss on contract termination for default			$ 24.4
Contractual Obligation, Due in Next Twelve Months							3.7
Contractual Obligation, Due in Second Year							4.2
Contractual Obligation, Due in Third Year							5.0
Contractual Obligation								13.7
Reserve established for contingency matters		0.9
Asset retirement obligations	$ 5.8