Fair Value Measurements - Value of Assets Measured at Fair Value on Non Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment of proved properties	$ 0	$ 502,233	$ 43,040	$ 502,233
Fair Value, Measurements, Nonrecurring | Natural Gas and Oil Properties
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	0	98,872	90,150	98,872
Impairment of proved properties	$ 0	$ 502,233	$ 43,040	$ 502,233