Supplemental Information on Oil and Natural Gas Producing Activities (Unaudited) - Standardized Measure of Discounted Future Cash Flows (Unaudited) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extractive Industries [Abstract]
Future cash inflows from production	$ 5,339,265	$ 4,621,615	$ 3,136,762
Future production costs	(1,996,689)	(1,837,852)	(1,454,798)
Future development costs	(1,170,113)	(966,203)	(665,516)
Future income tax expenses	0	(107)	(142)
Undiscounted future net cash flows	2,172,463	1,817,453	1,016,306
10% annual discount	(1,126,860)	(1,068,159)	(577,942)
Standardized measure of discounted future net cash flows	$ 1,045,603	$ 749,294	$ 438,364

No definition available.

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- Definition

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

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- Definition

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

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- Definition

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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- Definition

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

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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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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
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-Name Accounting Standards Codification
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