Supplementary Information - Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Future cash inflows	$ 221,542	$ 293,745
Future production costs	(115,091)	(191,227)
Future development costs	(31,870)	(30,586)
Future income tax expenses	(7,883)	(4,815)
Future Net Cash Flows	66,698	67,117
10% annual discount for estimated timing of cash flows	(14,461)	(8,315)
Standardized Measure of Discounted Future Net Cash Flows	$ 52,237	$ 58,802	$ 343,288

Amount of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for costs to be incurred in developing proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and gas reserves.

+ References

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-Publisher FASB
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Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for costs to be incurred in producing proved oil and gas reserves.

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Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year.

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Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves.

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