SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentrations (Details) - Customer Concentration Risk - Revenue Benchmark	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shell Trading US Company
Concentration Risk [Line Items]
Concentration risk, percentage	27.00%	26.00%	31.00%
Plains Marketing LP
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%
Vitol Midstream
Concentration Risk [Line Items]
Concentration risk, percentage	15.00%
Koch Supply & Trading LP
Concentration Risk [Line Items]
Concentration risk, percentage		15.00%	19.00%
Occidental Energy Marketing Inc.
Concentration Risk [Line Items]
Concentration risk, percentage		11.00%
Enterprise Crude Oil LLC
Concentration Risk [Line Items]
Concentration risk, percentage			11.00%