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Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Operations (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ (3,605) $ 3,966
Derivatives Designated as Cash-Flow Hedging Instruments [Member] | Interest Rate Swap [Member] | Interest Expense [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (7) (284)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Unrealized Gain (Loss) on Derivative Instruments, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (1,888) (2,273)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Natural Gas Commodity Contracts [Member] | Realized Gain (Loss) on Derivative Instruments, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income 20 3,017
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Unrealized Gain (Loss) on Derivative Instruments, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income (1,694) (14,628)
Derivatives Not Designated as Cash-Flow Hedging Instruments [Member] | Crude Oil Commodity Contracts [Member] | Realized Gain (Loss) on Derivative Instruments, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain/loss recognized in income $ (36) $ 18,134