STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS RELATING TO PROVED OIL, NATURAL GAS AND NATURAL GAS LIQUIDS RESERVES (UNAUDITED) (Principal Sources of Changes in Standardized Measure of Future Net Cash Flows) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Standardized Measure of Discontinued Future Net Cash Flows Relating to Proved Oil, Natural Gas and Natural Gas Liquids Reserves [Abstract]
Standardized measure at beginning of period	$ 436,433	$ 579,405	$ 371,117
Sales and transfers of oil, natural gas and natural gas liquids produced, net of production costs	(28,428)	(126,181)	(111,118)
Net changes in prices and production costs	(125,166)	48,322	202,810
Extensions, discoveries and improved recovery, less related costs	46	3,148	5,451
Development costs incurred during the period		16	2,261
Revisions and other	(54,980)	88,587	13,516
Accretion of 10% timing discount	50,963	58,222	37,356
Changes in income taxes	69,678	(70,390)	(371)
Changes in estimated future development costs	(5,502)	3,174	20,177
Changes in timing and other	(6,185)	21,551	8,302
Purchase of minerals in place			32,949
Sales of minerals in place	(229,923)	(169,421)	(3,045)
Standardized measure of discounted future net cash flows	$ 106,936	$ 436,433	$ 579,405
Accretion timing discount rate	10.00%	10.00%	10.00%