Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments (Net (Loss) Gain on Derivative Instruments) (Details)

v3.8.0.1
Derivative Instruments (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Derivative [Line Items]    
Net (loss) gain on natural gas, oil, and NGL derivatives $ (16,529) $ 99,577
Natural gas derivatives    
Derivative [Line Items]    
Net (loss) gain on natural gas, oil, and NGL derivatives (9,696) 86,277
Oil derivatives    
Derivative [Line Items]    
Net (loss) gain on natural gas, oil, and NGL derivatives (9,147) 10,905
Natural gas liquids derivatives    
Derivative [Line Items]    
Net (loss) gain on natural gas, oil, and NGL derivatives $ 2,314 $ 2,395