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Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Operations (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ (1,123) $ 7,753
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Unrealized gain (loss) on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (15) 305
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Realized gain (loss) on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (60) 191
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Unrealized gain (loss) on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (896) 6,251
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Realized gain (loss) on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ (152) $ 1,006