BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of accrued liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Accrued personnel costs	$ 0	$ 2,300
Accrued drilling and completion costs	5,021	2,849
Drilling advances	1,328	5,001
Accrued production expenses	3,326	2,926
Other accrued liabilities	3,885	1,718
Short-term operating lease liabilities	412
Total accrued liabilities	$ 13,972	$ 14,794