Supplemental Crude Oil and Natural Gas Information - Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Crude Oil and Natural Gas Information [Abstract]
Discount factor utilized as standardized measure for future net cash flows	10.00%
Future cash inflows	$ 42,574,897	$ 31,008,587	$ 36,551,672
Future production costs	(11,159,362)	(9,175,410)	(10,869,493)
Future development and abandonment costs	(6,487,097)	(6,452,647)	(6,935,958)
Future income taxes	(3,488,755)	(3,018,839)	(3,717,612)
Future net cash flows	21,439,683	12,361,691	15,028,609
10% annual discount for estimated timing of cash flows	(10,969,506)	(6,851,468)	(8,552,325)
Standardized measure of discounted future net cash flows	$ 10,470,177	$ 5,510,223	$ 6,476,284	$ 18,433,034