Acquisitions and Divestitures - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended	15 Months Ended	3 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Jul. 31, 2014	Sep. 30, 2014 Eagle Ford Shale, Lavaca County acre	Jul. 31, 2014 Eagle Ford Shale, Lavaca County	Sep. 30, 2014 South Texas Oil Gathering Sys. Development Rights	Sep. 30, 2014 Selma Chalk	Jun. 30, 2014 Selma Chalk	Mar. 31, 2014 South Texas Natural Gas Gathering Assets
Business Acquisition [Line Items]
Payments To Settle Obligations Assumed In Acquisition Net		$ (33,712,000)	$ 43,023,000	$ (22,500,000)
Purchased Oil and Gas Interests, Gross Area Of Property Acquired (in acres)						13,125
Proceeds from Sale of Intangible Assets								147,100,000
Impairment of Oil and Gas Properties	6,100,000									117,900,000
Business Combination, Disputed Contractual Adjustments, Settled in Arbitration	35,100,000
Proceeds from Sale of Oil and Gas Property and Equipment									67,900,000		96,000,000
Gain (Loss) on Sale of Oil and Gas Property								147,100,000			67,300,000
Sale Leaseback Transaction, Recognized Gain, Net								63,000,000			56,700,000
Sale Leaseback Transaction, Deferred Gain, Gross								84,100,000			10,600,000
Sale Leaseback Transaction, Current Period Gain Recognized	100,000	300,000
Sale Leaseback Transaction, Deferred Gain, Current	400,000	400,000
Sale Leaseback Transaction, Deferred Gain, Net	9,900,000	9,900,000
Purchased Oil and Gas Interests, Net Area Of Property Acquired (in acres)						11,660
Asset Acquisition, Purchase Price							45,600,000
Business Combination, Consideration Transferred						34,900,000
Business Combination, Consideration Transferred, Liabilities Incurred						10,700,000
Arbitration Settlement Interest					$ 1,300,000