Commodity Derivative Activities - Reconciliation of Gross Amounts to Amounts as Presented on Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Fair value of oil and natural gas derivatives - Current Assets	$ 1,319	$ 2,034
Fair value of oil and natural gas derivatives - Non-current Assets	1,087	566
Fair value of oil and natural gas derivatives - Current Liabilities	(1,414)	(1,002)
Fair value of oil and natural gas derivatives - Non-current Liabilities	(507)	(517)
Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value of oil and natural gas derivatives - Current Assets	1,319
Fair value of oil and natural gas derivatives - Non-current Assets	1,087
Fair value of oil and natural gas derivatives - Current Liabilities	(1,414)
Fair value of oil and natural gas derivatives - Non-current Liabilities	(507)
Total	485	$ 1,081
Fair Value, Inputs, Level 1 [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value of oil and natural gas derivatives - Current Assets	0
Fair value of oil and natural gas derivatives - Non-current Assets	0
Fair value of oil and natural gas derivatives - Current Liabilities	0
Fair value of oil and natural gas derivatives - Non-current Liabilities	0
Total	0
Fair Value, Inputs, Level 2 [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value of oil and natural gas derivatives - Current Assets	1,319
Fair value of oil and natural gas derivatives - Non-current Assets	1,087
Fair value of oil and natural gas derivatives - Current Liabilities	(1,414)
Fair value of oil and natural gas derivatives - Non-current Liabilities	(507)
Total	485
Fair Value, Inputs, Level 3 [Member] \| Commodity Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value of oil and natural gas derivatives - Current Assets	0
Fair value of oil and natural gas derivatives - Non-current Assets	0
Fair value of oil and natural gas derivatives - Current Liabilities	0
Fair value of oil and natural gas derivatives - Non-current Liabilities	0
Total	$ 0

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