Supplementary Information - Standardized Measure of Discounted Future Net Cash Flows and Changes therein Relating to Proved Oil and Gas Reserves (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Sales of oil and gas produced, net of production costs	$ (15,938)	$ (22,065)
Net changes in prices and production costs	(42,409)	24,826
Extensions, discoveries and improved recovery	31,276	46,885
Revisions of previous quantity estimates	(3,319)	1,942
Net change in development costs	(53,143)	3,062
Reserves sold	(113)	(274)
Reserves purchased	174	971
Accretion of discount	13,791	10,691
Net change in income taxes	5,572	(17,704)
Changes in production rates (timing) and other	7,812	(17,339)
Net change	(56,297)	30,995
Standardized measure of discounted future net cash flow:
Beginning of year	137,909	106,914
End of year	$ 81,612	$ 137,909