FAIR VALUE OF FINANCIAL INSTRUMENTS - Summary of recurring fair value measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total recurring fair value measurements	$ (4,441)	$ (6,869)
Oil and natural gas derivative swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	8,959	(3,932)
Oil and natural gas derivative collar contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	7,201	301
Net settlement provisions under ARM sales agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	(20,601)	(3,238)
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total recurring fair value measurements	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Oil and natural gas derivative swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Oil and natural gas derivative collar contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Net settlement provisions under ARM sales agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total recurring fair value measurements	16,160	(3,631)
Significant Other Observable Inputs (Level 2) | Oil and natural gas derivative swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	8,959	(3,932)
Significant Other Observable Inputs (Level 2) | Oil and natural gas derivative collar contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	7,201	301
Significant Other Observable Inputs (Level 2) | Net settlement provisions under ARM sales agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total recurring fair value measurements	(20,601)	(3,238)
Significant Unobservable Inputs (Level 3) | Oil and natural gas derivative swap contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Significant Unobservable Inputs (Level 3) | Oil and natural gas derivative collar contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	0	0
Significant Unobservable Inputs (Level 3) | Net settlement provisions under ARM sales agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring fair value measurements	$ (20,601)	$ (3,238)