Derivative Instruments - Impact of Derivative Activities on Condensed Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives	$ (21,084)	$ (6,891)	$ (119,679)	$ 109,879
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	(84)	32	(48)	(7,527)
Gain (Loss) on Commodity Derivative Instruments	(21,000)	(6,923)	(119,631)	117,406
Cash Settlements Interest Rate Swap Operating Activities	(973)	(919)	(2,851)	(1,287)
Cash Settlements Commodity Operating Activities	(21,265)	7,337	(43,190)	66,582
Cash settlements and premiums received (paid), net	$ (22,238)	$ 6,418	$ (46,041)	$ 65,295