Derivative Instruments - Summary of Gains and Losses on Derivative Instruments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ (40,535)	$ 15,812	$ (11,329)	$ 40,620
Not Designated as Hedging Instrument [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	(40,535)	15,812	(11,329)	40,620
Not Designated as Hedging Instrument [Member] | Gain (Loss) on Derivative Instruments [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	(40,603)	$ 15,812	(10,861)	$ 40,620
Not Designated as Hedging Instrument [Member] | Gain (Loss) on Derivative Instruments [Member] | Interest-Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ 68		$ (468)