Supplemental Oil and Gas Reserve Information - Unaudited - Changes in Standardized Measure of Discounted Future Net Cash Flows Applicable to Proved Oil and Natural Gas Reserves (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Standardized Measure of Discounted Future Net Cash Flows
January 1	$ 3,300,695	$ 2,483,065	$ 1,914,330
Net changes in prices and production costs	1,003,008	881,742	(367,527)
Net changes in future development costs	(89,304)	(60,929)	69,992
Sales of oil and natural gas, net	(1,155,223)	(769,367)	(403,739)
Purchases of reserves in place	385,763	6,518	533,505
Sales of reserves in place	(197,867)	(9,024)	(57,770)
Revisions of previous quantity estimates	(115,015)	(78,942)	333,398
Previously estimated development costs incurred	303,364	157,386	91,518
Accretion of discount	368,374	262,776	202,272
Net change in income taxes	(240,908)	(238,354)	(36,303)
Changes in timing and other	26,223	4,357	37,463
December 31	4,050,306	3,300,695	2,483,065
Extensions
Standardized Measure of Discounted Future Net Cash Flows
Proved oil and gas reserves increase	$ 461,196	$ 661,467	$ 165,926