Summary of Significant Accounting Policies - Schedule of Fair Value Impairments, Average Prices of Oil and Gas Properties And Applicable Discount Rates (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) $ / bbl $ / Mcf	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Fair Value And Impairments Oil And Gas Properties [Line Items]
Impairment of oil and gas properties	$ 544,714	$ 15	$ 547,101	$ 271
Oil Properties
Fair Value And Impairments Oil And Gas Properties [Line Items]
Fair Value	330,257		330,257
Impairment of oil and gas properties	$ 405,308
Management's Oil Price Outlook | $ / bbl	73.70
Management's Gas Price Outlook | $ / Mcf	4.04
Annual Discount Rate	10.00%
Natural Gas Properties
Fair Value And Impairments Oil And Gas Properties [Line Items]
Fair Value	$ 61,625		$ 61,625
Impairment of oil and gas properties	$ 139,406
Management's Oil Price Outlook | $ / bbl	75.91
Management's Gas Price Outlook | $ / Mcf	3.91
Annual Discount Rate	10.00%