Quarterly report pursuant to Section 13 or 15(d)

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

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DERIVATIVE INSTRUMENTS (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Derivative [Line Items]        
Net gain on natural gas, oil and NGL derivatives $ 26,971 $ 171,140 $ 125,237 $ 151,095
Natural gas derivatives        
Derivative [Line Items]        
Net gain on natural gas, oil and NGL derivatives 35,689 152,475 81,542 136,044
Oil derivatives        
Derivative [Line Items]        
Net gain on natural gas, oil and NGL derivatives (7,937) 11,871 44,937 11,417
NGL derivatives        
Derivative [Line Items]        
Net gain on natural gas, oil and NGL derivatives (781) 6,794 139 3,634
Contingent consideration arrangement        
Derivative [Line Items]        
Net gain on natural gas, oil and NGL derivatives $ 0 $ 0 $ (1,381) $ 0