REVENUE FROM CONTRACTS WITH CUSTOMERS (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]
Royalty income	$ 62,584	$ 71,080	$ 171,857	$ 201,950
Oil income
Disaggregation of Revenue [Line Items]
Royalty income	53,595	64,829	153,412	182,679
Natural gas income
Disaggregation of Revenue [Line Items]
Royalty income	3,331	2,181	4,909	4,946
Natural gas liquids income
Disaggregation of Revenue [Line Items]
Royalty income	$ 5,658	$ 4,070	$ 13,536	$ 14,325