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Financial Instruments - Effect of Derivative Instruments on Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Derivatives, Fair Value [Line Items]    
Derivative assets $ 2,394 $ 388
Derivative liabilities (98) (3,422)
Total derivative instruments 2,296 (3,034)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Derivative asset short-term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 63  
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Derivative asset long-term and other assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 7 44
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 (75) (5)
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 (10) (3)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Derivative asset short-term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 1,473 344
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Derivative asset long-term and other assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 713  
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   (1,504)
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   $ (1,910)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Liquid Contracts [Member] | Derivative asset short-term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets 138  
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Liquid Contracts [Member] | Derivative liability short-term [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liabilities $ (13)