Impact of Derivative Activities on Condensed Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives	$ (34,349)	$ 13,603	$ 116,770	$ (54,414)
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	(876)	0	(7,559)	0
Gain (Loss) on Commodity Derivative Instruments	(33,473)	13,603	124,329	(54,414)
Cash Settlements Interest Rate Swap Operating Activities	(436)	0	(368)	0
Cash Settlements Commodity Operating Activities	59,582	(8,301)	59,245	(3,907)
Cash settlements and premiums received (paid), net	$ 59,146	$ (8,301)	$ 58,877	$ (3,907)