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Financial Instruments - Effect of Derivative Instruments on Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Derivatives, Fair Value [Line Items]    
Derivative assets $ 6,088 $ 272
Derivative liabilities (13) (753)
Total derivative instruments (6,075) (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 426 146
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 (13) (38)
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 $ 5,662 126
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   $ (715)