Derivative Financial Instruments - Changes in Fair Value and Settlements of Commodity Derivative Contracts (Details) $ in Thousands  | 
3 Months Ended | 
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| 
 Mar. 31, 2019  
USD ($) 
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| Gain Loss On Derivative Instruments Net Pretax [Abstract] | |
| Derivative loss | $ 48,886 | 
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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