Derivative Instruments - Impact of Derivative Activities on Condensed Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives	$ (54,227)	$ (34,349)	$ (98,595)	$ 116,770
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	4	(876)	36	(7,559)
Gain (Loss) on Commodity Derivative Instruments	(54,231)	(33,473)	(98,631)	124,329
Cash Settlements Interest Rate Swap Operating Activities	(956)	(436)	(1,878)	(368)
Cash Settlements Commodity Operating Activities	(15,678)	59,582	(21,925)	59,245
Cash settlements and premiums received (paid), net	$ (16,634)	$ 59,146	$ (23,803)	$ 58,877