Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Producing Activities (Unaudited) - Discounted future cash flows (Detail)

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Supplemental Information on Oil and Gas Producing Activities (Unaudited) - Discounted future cash flows (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Supplemental Information on Oil and Gas Producing Activities (Unaudited)        
Future cash inflows computation period 12 months      
Percentage of net cash inflows that were discounted at annual rate 10.00% 10.00% 10.00%  
Annual net cash inflows        
Period of unweighted first day of the month average prices used to compute future cash inflows 12 months      
Future cash inflows $ 54,228 $ 64,199 $ 55,824  
Future production costs (36,524) (30,007) (26,375)  
Future development costs (2,772) (3,453) (3,312)  
Future net cash flows before income tax 14,932 30,739 26,137  
Future income tax expense (1,639) (5,505) (4,104)  
Future net cash flows 13,293 25,234 22,033  
10% annual discount for estimated timing of cash flows (7,824) (14,756) (13,406)  
Standardized measure of discounted future net cash flows $ 5,469 $ 10,478 $ 8,627 $ 3,287