REVENUE FROM CONTRACTS WITH CUSTOMERS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Royalty income	$ 32,444	$ 70,442	$ 109,273	$ 130,870
Oil income
Disaggregation of Revenue [Line Items]
Royalty income	27,617	65,863	99,817	117,850
Natural gas income
Disaggregation of Revenue [Line Items]
Royalty income	1,234	(1,074)	1,578	2,765
Natural gas liquids income
Disaggregation of Revenue [Line Items]
Royalty income	$ 3,593	$ 5,653	$ 7,878	$ 10,255