Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Derivative Instruments - Gain (Loss) on Derivative Instruments (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Derivative [Line Items]      
Gain due to changes in fair value of derivative instruments $ 213,679 $ (174,506) $ 203,513
Natural gas derivatives      
Derivative [Line Items]      
Gain due to changes in fair value of derivative instruments 232,143 (165,933) 182,993
Oil derivatives      
Derivative [Line Items]      
Gain due to changes in fair value of derivative instruments (3,350) (5,387) 19,201
Natural gas liquids derivatives      
Derivative [Line Items]      
Gain due to changes in fair value of derivative instruments $ (15,114) $ (3,186) $ 1,319