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Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Operations (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ 6,895 $ (3,663)
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 87 151
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Realized gain on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income 409 (8)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Unrealized loss on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income 854 (3,101)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Realized loss on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ 5,545 (876)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Liquid Contracts [Member] | Unrealized loss on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income   60
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Liquid Contracts [Member] | Realized gain (loss) on derivative instruments, net    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income   $ 111