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Financial Instruments - Effect of Derivative Instruments on Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
Jun. 30, 2020
Dec. 31, 2019
Derivatives, Fair Value [Line Items]    
Derivative assets $ 649 $ 272
Derivative liabilities (189) (753)
Total derivative instruments 460 (481)
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 334 146
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 (72) (38)
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 (48)  
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 315 126
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 $ (69) $ (715)