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Derivative Instruments and Hedging Activities - Narrative (Details)
Mcf in Millions
1 Months Ended 12 Months Ended
Jan. 31, 2016
$ / Mcf
Mcf
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Apr. 01, 2014
USD ($)
Derivative [Line Items]        
Unrealized losses included in accumulated other comprehensive income, reclassified into natural gas and crude oil revenues , pre-tax       $ 73,400,000
Unrealized losses included in accumulated other comprehensive income, reclassified into natural gas and crude oil revenues , net of tax   $ 0   $ 44,200,000
Gain (loss) on cash flow hedge ineffectiveness   $ 0 $ 0  
Subsequent Event | Energy Related Derivative | Derivatives designated as hedges | Swap        
Derivative [Line Items]        
Volume | Mcf 52.0      
Swaps weighted average price (USD per Mcf) | $ / Mcf 2.51