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Derivatives - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 9 Months Ended 1 Months Ended
Sep. 30, 2013
Mississippian Trust I
Sep. 30, 2013
Permian Trust
Sep. 30, 2013
Mississippian Trust II
Apr. 30, 2013
Interest Rate Swap
Apr. 30, 2013
Senior Floating Rate Notes due 2014
Fixed To Floating Interest Rate Swap Through April 1st 2013
Derivative Instruments and Hedging Activities Disclosure          
Notional amount of interest rate swaps         $ 350.0
Derivative, fixed interest rate         6.69%
Contract period end       Apr. 01, 2013  
Derivative agreement effective date Apr. 01, 2011 Aug. 01, 2011 Apr. 01, 2012    
Commodity derivative contracts covering volumes of oil and gas production, date Dec. 31, 2015 Mar. 31, 2015 Dec. 31, 2014