Supplemental Oil and Natural Gas Information - Changes in Standardized Measure of Discounted Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized Measure, beginning of the year	$ 729,686	$ 205,981	$ 212,865
Net change in prices and production costs	369,578	653,347	(33,507)
Net change in future development costs	87,466	(385,042)	1,552
Sales, less production costs	(321,802)	(226,324)	(99,768)
Extensions	363,708	135,734	79,941
Acquisitions	7,468	2,365	1,045
Divestitures	(20)		(5,231)
Revisions of previous quantity estimates	19,910	322,917	15,754
Previously estimated development costs incurred	65,035	34,102	4,886
Net changes in taxes	(37,345)
Accretion of discount	72,969	20,598	21,287
Changes in timing and other	(27,343)	(33,992)	7,157
Standardized Measure, end of year	$ 1,329,310	$ 729,686	$ 205,981