Supplementary Information on Oil and Gas Operations—Unaudited - Standardized Measure (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Future Net Cash Flows [Abstract]
Future cash flows	$ 482,766	$ 539,244	$ 299,035
Future production costs	(171,999)	(184,171)	(117,283)
Future development costs	(73,258)	(128,447)	(83,720)
Future income taxes	0	0	0
Future net cash flows	237,509	226,626	98,032
10% annual discount	(113,484)	(99,329)	(30,763)
Standardized measure of discounted future net cash flows	$ 124,025	$ 127,297	$ 67,269	$ 127,685

No definition available.

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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.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 33
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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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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
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