REVENUE - Summary of disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 12,770	$ 17,697
Crude oil
Disaggregation of Revenue [Line Items]
Revenues	12,362
Crude oil | Short-term contracts
Disaggregation of Revenue [Line Items]
Revenues	0
Crude oil | Long-term contracts
Disaggregation of Revenue [Line Items]
Revenues	12,362
Natural gas
Disaggregation of Revenue [Line Items]
Revenues	189	1,526
Natural gas | Short-term contracts
Disaggregation of Revenue [Line Items]
Revenues	47
Natural gas | Long-term contracts
Disaggregation of Revenue [Line Items]
Revenues	142
NGLs
Disaggregation of Revenue [Line Items]
Revenues	219	$ 1,470
NGLs | Short-term contracts
Disaggregation of Revenue [Line Items]
Revenues	54
NGLs | Long-term contracts
Disaggregation of Revenue [Line Items]
Revenues	$ 165