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Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Derivatives, Fair Value [Line Items]    
Derivative Asset, Current $ 2,658 $ 34,932
Document Period End Date Mar. 31, 2019  
Derivative liabilities $ 25,107 991
Derivative Asset, Noncurrent 229 10,100
Derivative Liability, Noncurrent 6,150 0
Derivative Liability 31,257 991
Derivative Asset 2,887 45,032
Commodity contracts    
Derivatives, Fair Value [Line Items]    
Derivative Liability 28,400  
Commodity contracts | Current Derivative Contract [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Current 2,658 34,932
Derivative liabilities 25,107 991
Commodity contracts | Noncurrent Derivative Contract [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Noncurrent 229 10,100
Derivative Liability, Noncurrent 6,150 0
Fair Value, Measurements, Recurring | Commodity contracts    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Current 2,658 34,932
Derivative liabilities (25,107) (991)
Derivative Asset, Noncurrent 229 10,100
Derivative Liability, Noncurrent $ 6,150 $ 0