Supplemental Oil and Natural Gas Information - Standardized Measure of Discounted Net Future Cash Flows (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Net Cash Flows [Abstract]
Future cash inflows (total revenues)	$ 4,750,238	$ 1,143,142	$ 975,664
Future production costs	(2,332,310)	(725,724)	(592,073)
Future development costs (capital costs)	(879,399)	(116,988)	(83,532)
Future net cash flows	1,538,529	300,430	300,059
10% annual discount for estimated timing of cash flows	(808,843)	(94,449)	(87,194)
Standardized measure of Discounted Future Net Cash Flow	$ 729,686	$ 205,981	$ 212,865	$ 330,657