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Financial Instruments - Effect of Derivative Instruments on Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Derivative assets $ 131 $ 57
Derivative liabilities (621) (3,639)
Total derivative instruments (490) (3,582)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 12  
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Other Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 19  
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Derivative Liability Short-Term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liabilities (88) (1,065)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Derivative liability Long Term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liabilities (75) (629)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 94  
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Other Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 6 57
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Derivative Liability Short-Term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liabilities (204) (1,482)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Derivative liability Long Term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liabilities $ (254) $ (463)