Supplemental Crude Oil and Natural Gas Information - Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Crude Oil and Natural Gas Information [Abstract]
Discount factor utilized as standardized measure for future net cash flows	10.00%
Future cash inflows	$ 36,551,672	$ 90,867,459	$ 78,646,274
Future production costs	(10,869,493)	(25,799,221)	(21,333,460)
Future development and abandonment costs	(6,935,958)	(12,842,174)	(10,250,789)
Future income taxes	(3,717,612)	(13,800,737)	(12,447,127)
Future net cash flows	15,028,609	38,425,327	34,614,898
10% annual discount for estimated timing of cash flows	(8,552,325)	(19,992,293)	(18,319,131)
Standardized measure of discounted future net cash flows	$ 6,476,284	$ 18,433,034	$ 16,295,767	$ 11,180,357