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Derivative Instruments - Narrative (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
Bcf
MBbls
Dec. 31, 2016
USD ($)
Bcf
MBbls
Derivative Instruments, Gain (Loss) [Line Items]    
Deferred net gains $ 4,600,000 $ 9,600,000
Net gains on derivative commodity instruments $ 4,600,000  
Percentage of derivative liability (up to) 100.00%  
Aggregate fair value of derivative instruments with credit-risk related contingencies $ 60,800,000  
Collateral posted $ 0  
Natural Gas Liquid Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Absolute quantities of derivative commodity instruments (in MMcf) | MBbls 8,943 1,095
Commodity Derivatives | Cash flow Hedges    
Derivative Instruments, Gain (Loss) [Line Items]    
Absolute quantities of derivative commodity instruments (in MMcf) | Bcf 2,148 646