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Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Operations (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ (1,787) $ (11,077)
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 82 (359)
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 90 124
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 (900) (7,148)
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 (1,302) (2,895)
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 (1) (645)
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 $ 244 $ (154)