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Financial Instruments - Effect of Derivative Instruments on Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Derivatives, Fair Value [Line Items]    
Derivative assets $ 118 $ 2,394
Derivative liabilities (3,574) (98)
Total derivative instruments (3,456) 2,296
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 2 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
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 (22) (75)
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)
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
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 (3,552)  
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 69 138
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Liquid Contracts [Member] | Derivative asset long-term and other assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative assets $ 47  
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)