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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, 2019
Dec. 31, 2018
Dec. 31, 2017
Standardized Measure of Discounted Future Net Cash Flows      
January 1 $ 4,050,306 $ 3,300,695 $ 2,483,065
Net changes in prices and production costs (1,070,192) 1,003,008 881,742
Net changes in future development costs 131,003 (89,304) (60,929)
Sales of crude oil and natural gas, net (943,989) (1,155,223) (769,367)
Purchases of reserves in place 0 385,763 6,518
Sales of reserves in place (36,907) (197,867) (9,024)
Revisions of previous quantity estimates (732,253) (115,015) (78,942)
Previously estimated development costs incurred 246,311 303,364 157,386
Accretion of discount 467,426 368,374 262,776
Net change in income taxes 533,872 (240,908) (238,354)
Changes in timing and other (238,908) 26,223 4,357
December 31 2,844,369 4,050,306 3,300,695
Extensions      
Standardized Measure of Discounted Future Net Cash Flows      
Proved oil and gas reserves increase $ 437,700 $ 461,196 $ 661,467