FAIR VALUE MEASUREMENTS - Summary of the Valuation of the Company's Financial Assets and Liabilities that were Accounted for at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets (Liabilities)
Total	$ (122,116)	$ (35,889)
Fair value on a recurring basis
Assets (Liabilities)
Total	(122,116)	(35,889)
Fair value on a recurring basis | Oil derivatives and basis swaps
Assets (Liabilities)
Derivative liability	(116,016)	(41,584)
Fair value on a recurring basis | Natural gas derivatives
Assets (Liabilities)
Derivative liability	(6,100)
Derivative asset		5,695
Fair value on a recurring basis | Level 1
Assets (Liabilities)
Total	0	0
Fair value on a recurring basis | Level 1 | Oil derivatives and basis swaps
Assets (Liabilities)
Derivative liability	0	0
Fair value on a recurring basis | Level 1 | Natural gas derivatives
Assets (Liabilities)
Derivative liability	0
Derivative asset		0
Fair value on a recurring basis | Level 2
Assets (Liabilities)
Total	(122,116)	(35,889)
Fair value on a recurring basis | Level 2 | Oil derivatives and basis swaps
Assets (Liabilities)
Derivative liability	(116,016)	(41,584)
Fair value on a recurring basis | Level 2 | Natural gas derivatives
Assets (Liabilities)
Derivative liability	(6,100)
Derivative asset		5,695
Fair value on a recurring basis | Level 3
Assets (Liabilities)
Total	0	0
Fair value on a recurring basis | Level 3 | Oil derivatives and basis swaps
Assets (Liabilities)
Derivative liability	0	0
Fair value on a recurring basis | Level 3 | Natural gas derivatives
Assets (Liabilities)
Derivative liability	$ 0
Derivative asset		$ 0