Risk Management and Derivative Instruments - Unrealized and Realized Gains and Losses Related to Derivative Instruments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments Gain Loss [Line Items]
(Gain) loss on commodity derivative instruments	$ (28,725)	$ 21,110	$ (19,231)	$ 67,218
Interest expense, net	(5,276)	(5,336)	(13,787)	(17,395)
Commodity derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
(Gain) loss on commodity derivative instruments	(28,725)	21,110	(19,231)	67,218
Interest rate derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Interest expense, net	$ (199)	$ 0	$ 334	$ 0