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Disclosures About Oil and Gas Producing Activities - Summary of Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Natural Gas Reserves (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Extractive Industries [Abstract]      
Standardized measure of discounted future net cash flows, Beginning balance $ 297,755 $ 460,395 $ 1,055,815
Net change in sales and transfer prices and in production (lifting) costs related to future production 229,139 (191,841) (1,405,864)
Changes in estimated future development costs (72,439) 17,405 231,900
Sales and transfers of oil and gas produced during the period (78,803) (62,835) (91,278)
Net change due to acquisition of minerals in place 17,331    
Net change due to extensions, discoveries and improved recovery 49,377 13,988 156,783
Net change due to revisions in quantity estimates (3,817) (25,236) (59,305)
Previously estimated development costs incurred during the period 43,202 15,884 146,237
Accretion of discount 30,789 46,040 105,582
Other (1,677) (9,500) 6,915
Net change in income taxes (49,826) 33,455 313,610
Standardized Measure of discounted future net cash flows $ 461,031 $ 297,755 $ 460,395