Property and Equipment - Capitalized Costs under Successful Efforts Method for Oil and Natural Gas Properties (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Oil and natural gas properties, proved	$ 170,237	$ 163,006
Oil and natural gas properties, unproved	14,911	15,695
Gross oil and natural gas properties	185,148	178,701
Accumulated depletion	(103,235)	(100,582)
Net oil and natural gas properties	81,913	78,119
Turkey [Member]
Property Plant And Equipment [Line Items]
Oil and natural gas properties, proved	169,758	162,494
Oil and natural gas properties, unproved	14,911	14,965
Bulgaria [Member]
Property Plant And Equipment [Line Items]
Oil and natural gas properties, proved	$ 479	512
Oil and natural gas properties, unproved		$ 730

Amount of accumulated depreciation, depletion and amortization of oil and gas property carried under the successful effort method. Oil and gas property include, but not limited to, the entity's wells and related equipment and facilities.

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Oil and Gas properties, gross, carried under the successful effort method.

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Oil and gas properties net of accumulated depreciation, depletion, amortization, impairment, and abandonment, carried under the successful effort method.

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Oil and Gas properties with proved reserves under the successful effort method.

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Oil and Gas properties with unproved reserves under the successful effort method.

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