Summary of Property and Equipment (Detail) (USD $)	3 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Apr. 24, 2013
Property, Plant and Equipment [Line Items]
Impairment of Oil and Gas Properties	$ 6,100,000
Impairment of Long-Lived Assets to be Disposed of		117,900,000
Oil and gas properties:
Proved	450,601,000		460,255,000
Unproved	137,464,000		101,520,000
Total oil and gas properties	588,065,000		561,775,000
Capitalized Costs, Proved Properties	2,743,466,000		2,593,700,000	267,688,000
Capitalized Costs, Support Equipment and Facilities	23,153,000		21,513,000
Property, Plant and Equipment, Other, Gross	2,766,619,000		2,615,213,000
Properties and equipment, gross, total	3,354,684,000		3,176,988,000
Accumulated depreciation, depletion and amortization	(1,011,781,000)		(939,684,000)
Property and equipment, net (successful efforts method)	$ 2,342,903,000		$ 2,237,304,000