Fair Value Measurements - Value of Assets Measured at Fair Value on Non Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment of proved properties	$ 0	$ 0	$ 0	$ 43,040	$ 87,941	$ 502,233	$ 0	$ 0	$ 43,040	$ 590,174	$ 28,024
Fair Value, Measurements, Nonrecurring | Natural Gas and Oil Properties
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value									90,150	152,230	15,605
Impairment of proved properties									$ 43,040	$ 590,174	$ 28,024