Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Derivative Instruments (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Derivative [Line Items]        
Net (loss) gain on natural gas, oil, and NGL derivatives $ (70,545) $ 64,871 $ (87,074) $ 164,448
Natural gas derivatives        
Derivative [Line Items]        
Net (loss) gain on natural gas, oil, and NGL derivatives (31,194) 56,668 (40,890) 142,945
Oil derivatives        
Derivative [Line Items]        
Net (loss) gain on natural gas, oil, and NGL derivatives (24,419) 8,143 (33,566) 19,048
Natural gas liquids derivatives        
Derivative [Line Items]        
Net (loss) gain on natural gas, oil, and NGL derivatives $ (14,932) $ 60 $ (12,618) $ 2,455