REVENUE - Summary of disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Revenues	$ 9,987	$ 11,597	$ 28,339	$ 50,868
Crude oil
Disaggregation Of Revenue [Line Items]
Revenues	8,250		25,917
Crude oil | Short-term contracts
Disaggregation Of Revenue [Line Items]
Revenues	8,250		8,313
Crude oil | Long-term contracts
Disaggregation Of Revenue [Line Items]
Revenues			17,604
Natural gas
Disaggregation Of Revenue [Line Items]
Revenues	995	694	1,284	2,570
Natural gas | Short-term contracts
Disaggregation Of Revenue [Line Items]
Revenues	120		183
Natural gas | Long-term contracts
Disaggregation Of Revenue [Line Items]
Revenues	875		1,101
NGLs
Disaggregation Of Revenue [Line Items]
Revenues	742	$ 697	1,138	$ 3,408
NGLs | Short-term contracts
Disaggregation Of Revenue [Line Items]
Revenues	89		162
NGLs | Long-term contracts
Disaggregation Of Revenue [Line Items]
Revenues	$ 653		$ 976